Littérature scientifique sur le sujet « SOX6, Cell differentiation »

ABSTRACT The Sry-related high-mobility-group box transcription factor Sox9 recruits the redundant L-Sox5 and Sox6 proteins to effect chondrogenesis, but the mode of action of the trio remains unclear. We identify here a highly conserved 359-bp sequence 10 kb upstream of the Agc1 gene for aggrecan, a most essential cartilage proteoglycan and key marker of chondrocyte differentiation. This sequence directs expression of a minimal promoter in both embryonic and adult cartilage in transgenic mice, in a manner that matches Agc1 expression. The chondrogenic trio is required and sufficient to mediate the activity of this enhancer. It acts directly, Sox9 binding to a critical cis-acting element and L-Sox5/Sox6 binding to three additional elements, which are cooperatively needed. Upon binding to their specific sites, L-Sox5/Sox6 increases the efficiency of Sox9 binding to its own recognition site and thereby robustly potentiates the ability of Sox9 to activate the enhancer. L-Sox5/Sox6 similarly secures Sox9 binding to Col2a1 (encoding collagen-2) and other cartilage-specific enhancers. This study thus uncovers critical cis-acting elements and transcription factors driving Agc1 expression in cartilage and increases understanding of the mode of action of the chondrogenic Sox trio.

Sox5 and Sox6 encode Sry-related transcription factors that redundantly promote early chondroblast differentiation. Using mouse embryos with three or four null alleles of Sox5 and Sox6, we show that they are also essential and redundant in major steps of growth plate chondrocyte differentiation. Sox5 and Sox6 promote the development of a highly proliferating pool of chondroblasts between the epiphyses and metaphyses of future long bones. This pool is the likely cellular source of growth plates. Sox5 and Sox6 permit formation of growth plate columnar zones by keeping chondroblasts proliferating and by delaying chondrocyte prehypertrophy. They allow induction of chondrocyte hypertrophy and permit formation of prehypertrophic and hypertrophic zones by delaying chondrocyte terminal differentiation induced by ossification fronts. They act, at least in part, by down-regulating Ihh signaling, Fgfr3, and Runx2 and by up-regulating Bmp6. In conclusion, Sox5 and Sox6 are needed for the establishment of multilayered growth plates, and thereby for proper and timely development of endochondral bones.

Abstract Sox6 belongs to the Sry (sex-determining region Y)–related high-mobility-group–box family of transcription factors, which control cell-fate specification of many cell types. Here, we explored the role of Sox6 in human erythropoiesis by its overexpression both in the erythroleukemic K562 cell line and in primary erythroid cultures from human cord blood CD34+ cells. Sox6 induced significant erythroid differentiation in both models. K562 cells underwent hemoglobinization and, despite their leukemic origin, died within 9 days after transduction; primary erythroid cultures accelerated their kinetics of erythroid maturation and increased the number of cells that reached the final enucleation step. Searching for direct Sox6 targets, we found SOCS3 (suppressor of cytokine signaling-3), a known mediator of cytokine response. Sox6 was bound in vitro and in vivo to an evolutionarily conserved regulatory SOCS3 element, which induced transcriptional activation. SOCS3 overexpression in K562 cells and in primary erythroid cells recapitulated the growth inhibition induced by Sox6, which demonstrates that SOCS3 is a relevant Sox6 effector.

The proprotein convertase furin participates in the maturation/bioactivation of a variety of proproteins involved in chondrogenesis events. These include parathyroid hormone-related peptide (PTHrP), an autocrine/paracrine factor that is crucial to both normal cartilage development and cartilage-related pathological processes. Despite the known importance of furin activity in the bioactivation of the polypeptides, the mechanisms that control furin regulation in chondrogenesis remain unknown. To gain insight into the molecular regulation of furin, we used the mouse prechondrogenic ATDC5 cell line, an established in vitro model of cartilage differentiation. Peak expression of both furin mRNA and furin PTHrP maturation was observed during chondrocyte nodule formation stage, an event that correlated with increased mRNA levels of Sox9, a potent high-mobility-group (HMG) box-containing transcription factor required for cartilage formation. Inhibition of furin activity led to a diminution in maturation of PTHrP, suggesting a relationship between Sox9-induced regulation of furin and chondrogenesis events. Transient transfection of Sox9 in nonchondrogenic cells resulted in a marked increase in furin mRNA and in the transactivation of the furin P1A promoter. Direct Sox9 action on the P1A promoter was narrowed down to a critical paired site with Sox9 binding capability in vitro and in vivo. Sox9 transactivation effect was inhibited by L-Sox5 and Sox-6, two Sox9 homologs also expressed in ATDC5 cells. Sox6 inhibitory effect was reduced when using Sox6-HMG-box mutants, indicating a repressive effect through direct HMG-box/DNA binding. Our work suggests a mechanism by which furin is regulated during chondrogenesis. It also adds to the complexity of Sox molecule interaction during gene regulation.

Sox9 is a transcription factor that plays an essential role in chondrogenesis and has been proposed to inhibit the late stages of endochondral ossification. However, the molecular mechanisms underlying the regulation of chondrocyte maturation and calcification by Sox9 remain unknown. In this study, we attempted to clarify roles of Sox9 in the late stages of chondrocyte differentiation. We found that overexpression of Sox9 alone or Sox9 together with Sox5 and Sox6 (Sox5/6/9) inhibited the maturation and calcification of murine primary chondrocytes and up-regulated parathyroid hormone–related protein (PTHrP) expression in primary chondrocytes and the mesenchymal cell line C3H10T1/2. Sox5/6/9 stimulated the early stages of chondrocyte proliferation and development. In contrast, Sox5/6/9 inhibited maturation and calcification of chondrocytes in organ culture. The inhibitory effects of Sox5/6/9 were rescued by treating with anti-PTHrP antibody. Moreover, Sox5/6/9 bound to the promoter region of the PTHrP gene and up-regulated PTHrP gene promoter activity. Interestingly, we also found that the Sox9 family members functionally collaborated with Ihh/Gli2 signaling to regulate PTHrP expression and chondrocyte differentiation. Our results provide novel evidence that Sox9 family members mediate endochondral ossification by up-regulating PTHrP expression in association with Ihh/Gli2 signaling.

Metformin has recently emerged as a key player in promotion of neuroblastoma differentiation and neurite outgrowth. However, molecular mechanisms of how metformin promotes cellular differentiation have not yet been fully elucidated. In this study, we investigated how metformin promotes cell differentiation, via an inhibition of cell proliferation, by culturing SH-SY5Y neuroblastoma cells with or without metformin. Pretreatment with reactive oxygen species (ROS) scavenger, NAC, revealed that ROS plays a crucial role in induction of cell differentiation. Cell differentiation was observed under various morphological criteria: extension of neuritic processes and neuronal differentiation markers. Treatment with metformin significantly increased neurite length, number of cells with neurite, and expression of neuronal differentiation markers, β-tubulin III and tyrosine hydroxylase (TH) compared with untreated control. Further investigation found that metformin significantly decreased Cdk5 but increased Sox6 during cell differentiation. Analysis of the mechanism underlying these changes using Cdk5 inhibitor, roscovitine, indicated that expressions of Cdk5 and Sox6 corresponded to metformin treatment. These results suggested that metformin produces neuronal differentiation via Cdk5 and Sox6. In addition, phosphorylated Erk1/2 was decreased while phosphorylated Akt was increased in metformin treatment. Taken together, these findings suggest that metformin promotes neuronal differentiation via ROS activation through Cdk5/Sox6 crosstalk, relating to Erk1/2 and Akt signaling.

Abstract SOX8, SOX9 and SOX10 compose the SOXE transcription factor group. They govern cell fate and differentiation in many lineages, and mutations impairing their activity cause severe diseases, including campomelic dysplasia (SOX9), sex determination disorders (SOX8 and SOX9) and Waardenburg-Shah syndrome (SOX10). However, incomplete knowledge of their modes of action limits disease understanding. We here uncover that the proteins share a bipartite transactivation mechanism, whereby a transactivation domain in the middle of the proteins (TAM) synergizes with a C-terminal one (TAC). TAM comprises amphipathic α-helices predicted to form a protein-binding pocket and overlapping with minimal transactivation motifs (9-aa-TAD) described in many transcription factors. One 9-aa-TAD sequence includes an evolutionarily conserved and functionally required EΦ[D/E]QYΦ motif. SOXF proteins (SOX7, SOX17 and SOX18) contain an identical motif, suggesting evolution from a common ancestor already harboring this motif, whereas TAC and other transactivating SOX proteins feature only remotely related motifs. Missense variants in this SOXE/SOXF-specific motif are rare in control individuals, but have been detected in cancers, supporting its importance in development and physiology. By deepening understanding of mechanisms underlying the central transactivation function of SOXE proteins, these findings should help further decipher molecular networks essential for development and health and dysregulated in diseases.

Abstract Erythropoiesis, the essential process of hematopoietic stem cell development into erythrocytes, is controlled by lineage-specific transcription factors that determine cell fate and differentiation and by the hormone erythropoietin that stimulates cell survival and proliferation. Here we identify the Sry-related high-mobility-group (HMG) box transcription factor Sox6 as an important enhancer of definitive erythropoiesis. Sox6 is highly expressed in proerythroblasts and erythroblasts in the fetal liver, neonatal spleen, and bone marrow. Mouse fetuses and pups lacking Sox6 develop erythroid cells slowly and feature misshapen, short-lived erythrocytes. They compensate for anemia by elevating the serum level of erythropoietin and progressively enlarging their erythropoietic tissues. Erythroid-specific inactivation of Sox6 causes the same phenotype, demonstrating cell-autonomous roles for Sox6 in erythroid cells. Sox6 potentiates the ability of erythropoietin signaling to promote proerythroblast survival and has an effect additive to that of erythropoietin in stimulating proerythroblast and erythroblast proliferation. Sox6 also critically facilitates erythroblast and reticulocyte maturation, including hemoglobinization, cell condensation, and enucleation, and ensures erythrocyte cytoskeleton long-term stability. It does not control adult globin and erythrocyte cytoskeleton genes but acts by stabilizing filamentous actin (F-actin) levels. Sox6 thus enhances erythroid cell development at multiple levels and thereby ensures adequate production and quality of red blood cells.

SOX6 plays important roles in cell proliferation, differentiation, and cell fate determination. It has been confirmed that SOX6 is a tumor suppressor and downregulated in various cancers, including esophageal squamous cell carcinoma, hepatocellular carcinoma, and chronic myeloid leukemia. Netrin-1 is highly expressed in various human cancers and acts as an anti-apoptotic and proangiogenic factor to drive tumorigenesis. The role of SOX6 and netrin-1 in regulating the growth of ovarian tumor cells still remains unclear. Real-time polymerase chain reaction and western blot were used to determine the SOX6 messenger RNA and protein levels, respectively, in ovarian cancer cells and tumor tissues. Stable transfection of SOX6 was conducted to overexpress SOX6 in PA-1 and SW626 cells. Cell viability was measured by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. Invasion of ovarian cancer cells and migration of human umbilical vein endothelial cells were confirmed by Transwell assays. To overexpress netrin-1, ovarian cancer cells with SOX6 restoration was transduced with netrin-1 lentiviral particles. PA-1 xenografts in a nude mice model were used to conduct in vivo evaluation of the role of SOX6 and its relationship with netrin-1 in tumor growth and angiogenesis. In this study, we found significantly reduced SOX6 levels in PA-1, SW626, SK-OV-3, and CaoV-3 ovarian cancer cell lines and human tumor tissues in comparison with normal human ovarian epithelial cells or matched non-tumor tissues. SOX6 overexpression by stable transfection dramatically inhibited proliferation and invasion of PA-1 and SW626 cells. Also, conditioned medium from PA-1 and SW626 cells with SOX6 restoration exhibited reduced ability to induce human umbilical vein endothelial cells migration and tube formation compared with conditioned medium from the cells with transfection control. Furthermore, an inverse relationship between SOX6 and netrin-1 expression was observed in PA-1 and SW626 cells. Overexpression of netrin-1 in ovarian cancer cells with forced SOX6 expression remarkably abrogated the inhibitory effect of SOX6 on proliferation, invasion of the cells, and tumor xenograft growth and vascularity in vivo. Human umbilical vein endothelial cell migration and tube formation were enhanced in the conditioned medium from the ovarian cancer cells transduced with netrin-1 lentivirus particles. Our observations revealed that SOX6 is a tumor suppressor in ovarian cancer cells, and SOX6 exerts an inhibitory effect on the proliferation, invasion, and tumor cell-induced angiogenesis of ovarian cancer cells, whereas nerin-1 plays an opposite role and its expression is inversely correlated with SOX6. Moreover, our findings suggest a new role of SOX6 and netrin-1 for understanding the progression of ovarian cancer and have the potential for the development of new diagnosis and treatment strategies for ovarian cancer.

Cell-based or pharmacological approaches for promoting tendon repair are currently not available because the molecular mechanisms of tendon development and healing are not well understood. Although analysis of knockout mice provides many critical insights, small animals such as mice have some limitations. In particular, precise physiological examination for mechanical load and the ability to obtain a sufficient number of primary tendon cells for molecular biology studies are challenging using mice. Here, we generated Mohawk (Mkx)−/− rats by using CRISPR/Cas9, which showed not only systemic hypoplasia of tendons similar to Mkx−/− mice, but also earlier heterotopic ossification of the Achilles tendon compared with Mkx−/− mice. Analysis of tendon-derived cells (TDCs) revealed that Mkx deficiency accelerated chondrogenic and osteogenic differentiation, whereas Mkx overexpression suppressed chondrogenic, osteogenic, and adipogenic differentiation. Furthermore, mechanical stretch stimulation of Mkx−/− TDCs led to chondrogenic differentiation, whereas the same stimulation in Mkx+/+ TDCs led to formation of tenocytes. ChIP-seq of Mkx overexpressing TDCs revealed significant peaks in tenogenic-related genes, such as collagen type (Col)1a1 and Col3a1, and chondrogenic differentiation-related genes, such as SRY-box (Sox)5, Sox6, and Sox9. Our results demonstrate that Mkx has a dual role, including accelerating tendon differentiation and preventing chondrogenic/osteogenic differentiation. This molecular network of Mkx provides a basis for tendon physiology and tissue engineering.

SOX6 is a transcription factor (TF) belonging to the Sry-related HMG-box TFs family. It controls terminal differentiation and lineage specification of many cell types, by mediating cell cycle withdrawal and activation of lineage specific genes. In hematopoiesis, Sox6 sustains cell survival, proliferation and terminal maturation of murine erythroid cells. To explore the role of SOX6 in human erythropoiesis, we first overexpressed it in erythroleukemic BCR-ABL+ K562 cell line. In these cells, Sox6 overexpression induces a strong erythroid differentiation coupled with growth arrest. This last effect may be mediated by SOCS3 (Suppressor Of Cytokines Signalling 3), that is a direct transcriptional target of SOX6. SOCS3 represses two important pathways in erythropoiesis: the IGF1/IGF1R pathway, in response to insulin-like growth factor 1 (IGF1) and the Epo-Jak-STAT pathway, in response to erythropoietin. In particular, in K562 cells, proliferation depends on autocrine IGF1 signalling, induced by BCR-ABL. Cells overexpressing Sox6 or SOCS3 display a reduction in IGF1 expression, suggesting that SOX6 plays a pivotal role in blocking cell proliferation through SOCS3 upregulation and by inhibiting the BCR-ABL-dependent IGF1 signalling. Leukemias and myelodisplasias are characterized by a block in differentiation leading to an excess of proliferating immature cells. Since SOX6 is a potent inducer of growth arrest and differentiation, I investigated the effect of its ectopic expression in different model systems of leukemia, to enforce these cells to overcome their pathological conditions. Therefore, I used leukemic model systems that varies for their degrees of differentiation/maturation and to the presence/absence of specific genetic lesions (i.e. BCR-ABL fusion oncogene, JAK2V617F mutation). Sox6 overexpression blocks proliferation in all the tested BCR-ABL+ cell lines (erythroleukemic K562, megakaryoblastic MEG.01) and surprisingly even in the lymphoblastic SUPB15 and B-ALL BCR-ABL GFP+. The JAK2V617F mutation, typical of myelodysplastic syndromes, makes cells unresponsive to SOCS3. Remarkably, in JAK2V617F+ cell lines (thrombocythemic UKE1 and SET2; erythroleukemic HEL), Sox6 overexpression induces a block in cellular proliferation strictly dependent on the copy number of the JAK2V617F alleles, further confirming SOCS3 as a key effector of SOX6. A second aspect controlled by SOX6 is the activation of a set of specific erythroid genes that lead erythroblastic progenitors to undergo terminal differentiation. Indeed, Sox6 overexpression enhances erythroid differentiation in bipotent megakaryoblastic and erythroleukemic cells (K562 and HEL) and enforces megakaryoblastic cells towards an erythroid fate (MEG.01, SET2 and UKE1). Surprisingly, Sox6 overexpression is capable of downregulating genes essential for B-cells identity (i.e. PAX5), whereas it is not sufficient to activate an erythroid program in lymphoblastic cells (SUPB15 and B-ALL BCR-ABL GFP+). Taken together, these findings suggest that SOX6 plays a major role in activating cell cycle withdrawal, acting on SOCS3, and interferes with cell fate decision by downregulating specific cellular programs and enforcing, where possible, an erythroid lineage choice in leukemic and myelodysplastic cell lines. Finally, I explored the impact of SOX6 ectopic expression in B-ALL BCR-ABL GFP+ capability to engraft and generate leukemia in C57BL/6J mice. B-ALL BCR-ABL GFP+ SOX6+ cells are not capable to engraft recipient mice, suggesting that SOX6 overexpression in such cellular model interferes with the onset of leukemia. Taken together, these results strongly point to a pivotal role for SOX6 in suppressing cells proliferation both in vitro and in vivo, and pave the way for the identification of potential druggable targets to develop new therapeutical approaches for leukemic and myelodysplastic syndromes.

The main focus of our laboratory is clarifying the roles of DNA binding proteins belonging to the HMG box superfamily during embryonic development. In particular, I studied Sox18 and Sox7 in zebrafish and our data show that they act redundantly in vascular development. Mutations in SOX18 have been associated with Hypotrichosis-Lymphedema-Telangiectasia (HLT), a human syndrome combining defects in hair follicle, blood and lymphatic vessels development. Similarly, spontaneous mutations in Sox18 underlie cardiovascular and hair follicle defects in ragged mice, including symptoms of lymphatic dysfunction. On the other hand, mice null for Sox18 display only mild coat defects. This suggests that other Sox proteins may compensate for the absence of Sox18. zfsox18 and zfsox7 genes are co-expressed in endothelial cells and their precursors. Knock down of either genes had minimal effects on blood vessels, however their simultaneous knockdown selectively affects trunk/tail blood circulation: endothelial cells that fail to acquire the proper arteriovenous identity and multiple fusions are present between the major axial vessels. To identify the hypothetical targets of sox18 and sox7 I performed a genome wide analysis using Affymetrix chip. We compared the expression of control embryos and double knockdown at two different time points: during initial steps of blood vessels formation and around the time when circulation begins. Functional studies of the most interesting identified genes will follow.

Sox1 is upregulated during ES cell differentiation into neural precursors, and its misexpression causes an EC cell line to differentiate into neurons. Sox1 expression during nervous system development is associated with proliferating cells of the CNS, expression being lost as cells exist mitosis and terminally differentiate. Its expression pattern is more restricted than that of most other markers for early neural cells such as nestin, making it a good marker gene for the study of neural development both in vivo and in vitro from ES cells. Here I have used gene targeting to generate a reporter ES cell line (46C) in which the Sox1 open reading frame is replaced by the gene encoding enhanced green fluorescent protein linked to a selectable marker. The use of EGFP enables the observation of Sox1 expression in live cells. The expression of the reporter faithfully recapitulates the normal expression of Sox1 in vivo in mice generated from the 46C cells. This cell line has been used to analyse the differentiation of ES cells to neural fates, in particular to characterise a newly discovered, monoculture differentiation system. Sox1-EGFP expression is monitored by flow cytometry, which enables quantification of the differentiation process. The effect of proteins and inhibitors implicated in neural determination has been monitored quantitatively and over time using this system. Acquisition of neural fate occurs rapidly in the absence of any inducers or serum, and without formation of multicellular aggregates. BMP-4 completely blocks this neural fate specification, similarly to the situation in the frog and the chick. Collectively, the results indicate that restriction of ES cells pluripotency to neural fates occurs in a manner resembling default neural induction in amphibians.

The transcription factor Sox2 has a key role not only in maintaining stem state but also in specification of neural fate of embryonic cells. Multiple regulatory elements have been identified in the Sox2 locus (Uchikawa et al, 2003). In the developing embryo, these regulatory elements are activated differentially in time and space. We studied the activity of 25 defined regulatory elements of the Sox2 promoter in three different lines of chick ES cells. By transfection of plasmids encoding Enhanced Green Fluorescent Protein (EGFP) and the minimal promoter thymidine kinase (tk) coupled with individual Sox2 regulatory elements we find that the Sox2 enhancer N2 has the highest activity in proliferating chick cell lines compared with other enhancer regions. Under conditions that induce ES cells to differentiate into neurons the activity of the N2 enhancer increased along with an increase in levels of expression of Sox2 mRNA. Further analysis of the N2 enhancer sequence identified two subregions with 176 and 73 base pairs (bp) which are highly conserved between chick, mouse and man. Functional studies performed with the tk-EGFP reporter plasmids under the control of five regulatory sequences containing the mouse N2 enhancer in its full length, its two sub-regions (176 and 73 bp) or sequences composed of the full length of the mouse N2 from which each of the two sub-regions 176 bp and 73 bp has been deleted confirmed that the two sub-regions of the N2 enhancer account for its activity in both proliferating cES cells as well as their induced neural differentiation state. These findings suggest that N2 core regulatory regions encode conserved instructions required to direct expression of Sox2 both in embryonic stem cells induced to neural differentiation and in the neural plate of the embryo itself.

This study examined the role of heparan sulfate proteoglycans (HSPGs) in neural lineage differentiation of human mesenchymal stem cells (hMSCs). Several HSPGs were identified as potential new targets controlling neural fate specification and may be applied to the development of improved models to examine and repair brain damage. hMSCs were characterised throughout extended in vitro expansion for neural lineage potential (neurons, astrocytes, oligodendrocytes) and differentiated using terminal differentiation and intermediate sphere formation. Brain damage and neurological disorders caused by injury or disease affect a large number of people often resulting in lifelong disabilities. Multipotent mesenchymal stem cells have a large capacity for self-renewal and provide an excellent model to examine the regulation and contribution of both stem cells and their surrounding microenvironment to the repair of neural tissue damage.

Thesis (Ph.D.)--Kent State University, 2005.
Title from PDF t.p. (viewed Sept. 5, 2006). Advisor: Walter E. Horton. Keywords: chondrocytes; osteoarthritis; Sox9; Bcl-2; MEK-ERK 1/2. Includes bibliographical references (p. 91-106).

The aims of this PhD research were: to examine molecular mechanisms underlying the transcriptional regulation of the Sox2 gene during forebrain development; to examine the role of Sox2 for the proper neuronal differentiation of neural stem cells; and to examine the role of Sox2 in controlling the maintenance of neural stem cells (in vivo and in vitro). The aim of the first work (Chapter 1) was to investigate the transcription factors and the regulatory sequences that control transcription of the Sox2 gene in the developing brain and neural stem cells. Our laboratory previously identified Sox2 regulatory sequences able to drive expression of a reporter β-geo transgene to neural stem cells of the brain in transgenic mice. I focused on two mouse forebrain-specific enhancers able to recapitulate Sox2 telencephalic expression throughout forebrain development, also active in neural stem cells of the adult and embryonic brain (Sox2 5’ and 3’ enhancers). This work showed that Emx2 acts as a direct transcriptional repressor of both Sox2 telencephalic enhancers, acting in two different ways to repress their transcriptional activity: by directly binding to a specific site within these regulatory elements, thus preventing the binding of activators, or possibly by protein to protein interaction sequestring the activators, thus antagonizing their activity. By the study of double mutant mice (expressing reduced levels of Sox2 and Emx2) we further found that Emx2 deficiency counteracts (at least in part) the deleterious effects of Sox2 deficiency on neural stem cell proliferation ability in the postnatal hippocampus, and also rescued other brain morphological abnormalities of Sox2-deficient mutants. It is likely possible that a simultaneous decrease of Emx2 levels (a Sox2 repressor) may antagonize these defects, by restoring Sox2 levels. In the second line of my research (Chapter 2) we performed in vitro differentiation studies on neural stem cells cultured from embryonic and adult brains of Sox2 “knockdown” mutants (expressing reduced levels of Sox2) where Sox2 deficiency impairs neuronal differentiation. In particular, my contribution to this work was to evaluate the in vitro differentiation defects of Sox2 mutant neurospheres by immunofluorescence staining for different glial and neuronal markers. Strikingly, I observed that mutant cells produce reduced numbers of mature neurons (in particular GABAergic neurons), but generate normal glia. Most of the cells belonging to the neuronal lineage failed to progress to mature neurons showing morphological abnormalities. To evaluate if restoration of Sox2 levels is able to rescue the differentiation defects of mutant cells, I engineered Sox2-expressing lentiviral vector, which I used to infect neural cells at early or late differentiation stages. I found that, Sox2 overexpression is able to rescue the neuronal maturation defects of mutant cells only if administered at early stages of differentiation. Further, I observed that Sox2 suppresses the endogenous GFAP gene, a marker of glial differentiation. These results suggests that Sox2 is required in early in vitro differentiating neuronal cells, for maturation and for suppression of alternative lineage markers. The third research (Chapter 3) investigated neurogenesis and neural stem cells properties in mice carrying a conditional mutation in the Sox2 gene (Sox2flox). Here, Sox2 was deleted via a nestin-Cre transgene that leads to complete Sox2 loss in the central nervous system by 12.5 dpc. These studies showed that embryonic neurogenesis was not importantly defective, however shortly after birth, NSC and neurogenesis are completely lost in the hippocampus. The expression of cytokine-encoding genes, essential for stem cell niche, is also strongly perturbed and leads to impaired stem cell maintenance (in vivo and in vitro). In vitro, NSC cultures derived from Sox2-deleted forebrain become rapidly exhausted, losing their proliferation and self-renewal properties. In Sox2-deleted neurospheres, Shh is extremely downregulated. However, the conditioned medium from wild type NSC cultures or the administration of a Shh agonist efficiently rescue the proliferation defects. These results suggest that the effect of Sox2 on neural stem cells growth and maintenance is partially mediated by Shh secretion, and that the Shh gene must be a direct target of Sox2. To confirm this hypothesis, I infected Sox2-deleted NSC with a Sox2-IRES-GFP expressing lentivirus just prior to the beginning of the growh decline, and I observed that the re-expression of Sox2 induces the ability to re-express Shh and rescues the formation of neurosphere. These findings indicate that NSC control their status, at least in part, through non cell-autonomous mechanisms (such as activation of important cytochine-encoding genes) which depend on Sox2.

Dans le contexte de la physiologie comparée de la reproduction, les amphibiens sont peu étudiés. Le travail réalisé durant cette thèse visait à analyser des marqueurs de différenciation testiculaire chez l'urodèle Pleurodeles waltl, dont le déterminisme génétique du sexe (ZZ/ZW) peut être influencé par la température. Nos études ont d'abord porté sur le gène sox9 marqueur de la différenciation testiculaire chez les vertébrés supérieurs. Le gène cloné chez le pleurodèle montre une bonne conservation par rapport aux autres vertébrés. Son expression plus élevée dans la gonade mâle n'apparaît que tardivement suggérant qu'il n'est probablement pas impliqué dans les stades précoces de la différenciation testiculaire. En outre, son expression dans le mésonéphros rend difficile son utilisation comme marqueur de différenciation testiculaire. Nous avons ensuite étudié l'Amh, hormone testiculaire impliquée dans la régression des canaux de Müller chez de nombreux vertébrés. Son expression spécifique de la gonade, précocement plus élevée chez les larves ZZ que les ZW en font un excellent marqueur de la différenciation testiculaire. Le fait que les pleurodèles mâles voient les canaux de Müller persister malgré la présence d'Amh suggère que la fonction primaire de cette hormone était en relation avec la différenciation gonadique et que la fonction de régression des canaux de Müller n'est apparue que secondairement au cours de l'évolution. Ces marqueurs ont été mis à profit pour caractériser le phénotype gonadique lors d'inversions sexuelles ou lors de développements en absence de cellules germinales. Ils ont permis de montrer que les cellules germinales ne semblent pas jouer de rôle dans la différenciation gonadique du pleurodèle
In the context of comparative physiology of reproduction, amphibians are poorly studied. This work was dedicated to the analysis of testis differentiation markers in the newt Pleurodeles waltl, which shows a ZZ/ZW genetic mode of sex determination that can be affected by temperature. First, we studied sox9, a testis differentiation marker well characterized in many higher vertebrates. The gene cloned in Pleurodeles shows a good level of identity with other vertebrates. The testis-enriched expression appears late during the testis differentiation process indicating that it is probably not involved in the early steps of testis differentiation. Its use as a marker of testicular differentiation proved difficult since it is expressed not only in the gonads but also in the mesonephros. Then, we studied amh, a testis hormone responsible for müllerian duct regression in many vertebrates. Its early expression in the gonad, significantly higher in male than in female larvae makes it an excellent marker for testis differentiation. Since in Pleurodeles waltl, Müllerian ducts persist in males, it suggests that during the course of evolution, the function of Amh on the regression of Müllerian ducts appeared secondarily after its role in gonadal differentiation. These markers have been used to characterize the gonadal phenotype during sex reversal, or in gonads developed in the absence of germ cells. They showed that these cells do not seem to play a role in gonadal differentiation of Pleurodeles waltl

Cell based therapies require cells capable of self renewal and differentiation, and a prerequisite is the ability to prepare an effective dose of ex vivo expanded cells for autologous transplants. The in vivo identification of a source of physiologically relevant cell types suitable for cell therapies is therefore an integral part of tissue engineering. Bone marrow is the most easily accessible source of mesenchymal stem cells (MSCs), and harbours two distinct populations of adult stem cells; namely hematopoietic stem cells (HSCs) and bone mesenchymal stem cells (BMSCs). Unlike HSCs, there are yet no rigorous criteria for characterizing BMSCs. Changing understanding about the pluripotency of BMSCs in recent studies has expanded their potential application; however, the underlying molecular pathways which impart the features distinctive to BMSCs remain elusive. Furthermore, the sparse in vivo distribution of these cells imposes a clear limitation to their in vitro study. Also, when BMSCs are cultured in vitro there is a loss of the in vivo microenvironment which results in a progressive decline in proliferation potential and multipotentiality. This is further exacerbated with increased passage number, characterized by the onset of senescence related changes. Accordingly, establishing protocols for generating large numbers of BMSCs without affecting their differentiation potential is necessary. The principal aims of this thesis were to identify potential molecular factors for characterizing BMSCs from osteoarthritic patients, and also to attempt to establish culture protocols favourable for generating large number of BMSCs, while at the same time retaining their proliferation and differentiation potential. Previously published studies concerning clonal cells have demonstrated that BMSCs are heterogeneous populations of cells at various stages of growth. Some cells are higher in the hierarchy and represent the progenitors, while other cells occupy a lower position in the hierarchy and are therefore more committed to a particular lineage. This feature of BMSCs was made evident by the work of Mareddy et al., which involved generating clonal populations of BMSCs from bone marrow of osteoarthritic patients, by a single cell clonal culture method. Proliferation potential and differentiation capabilities were used to group cells into fast growing and slow growing clones. The study presented here is a continuation of the work of Mareddy et al. and employed immunological and array based techniques to identify the primary molecular factors involved in regulating phenotypic characteristics exhibited by contrasting clonal populations. The subtractive immunization (SI) was used to generate novel antibodies against favourably expressed proteins in the fast growing clonal cell population. The difference between the clonal populations at the transcriptional level was determined using a Stem Cell RT2 Profiler TM PCR Array which focuses on stem cell pathway gene expression. Monoclonal antibodies (mAb) generated by SI were able to effectively highlight differentially expressed antigenic determinants, as was evident by Western blot analysis and confocal microscopy. Co-immunoprecipitation, followed by mass spectroscopy analysis, identified a favourably expressed protein as the cytoskeletal protein vimentin. The stem cell gene array highlighted genes that were highly upregulated in the fast growing clonal cell population. Based on their functions these genes were grouped into growth factors, cell fate determination and maintenance of embryonic and neural stem cell renewal. Furthermore, on a closer analysis it was established that the cytoskeletal protein vimentin and nine out of ten genes identified by gene array were associated with chondrogenesis or cartilage repair, consistent with the potential role played by BMSCs in defect repair and maintaining tissue homeostasis, by modulating the gene expression pattern to compensate for degenerated cartilage in osteoarthritic tissues. The gene array also presented transcripts for embryonic lineage markers such as FOXA2 and Sox2, both of which were significantly over expressed in fast growing clonal populations. A recent groundbreaking study by Yamanaka et al imparted embryonic stem cell (ESCs) -like characteristic to somatic cells in a process termed nuclear reprogramming, by the ectopic expression of the genes Sox2, cMyc and Oct4. The expression of embryonic lineage markers in adult stem cells may be a mechanism by which the favourable behaviour of fast growing clonal cells is determined and suggests a possible active phenomenon of spontaneous reprogramming in fast growing clonal cells. The expression pattern of these critical molecular markers could be indicative of the competence of BMSCs. For this reason, the expression pattern of Sox2, Oct4 and cMyc, at various passages in heterogeneous BMSCs population and tissue derived cells (osteoblasts and chondrocytes), was investigated by a real-time PCR and immunoflourescence staining. A strong nuclear staining was observed for Sox2, Oct4 and cMyc, which gradually weakened accompanied with cytoplasmic translocation after several passage. The mRNA and protein expression of Sox2, Oct4 and cMyc peaked at the third passage for osteoblasts, chondrocytes and third passage for BMSCs, and declined with each subsequent passage, indicating towards a possible mechanism of spontaneous reprogramming. This study proposes that the progressive decline in proliferation potential and multipotentiality associated with increased passaging of BMSCs in vitro might be a consequence of loss of these propluripotency factors. We therefore hypothesise that the expression of these master genes is not an intrinsic cell function, but rather an outcome of interaction of the cells with their microenvironment; this was evident by the fact that when removed from their in vivo microenvironment, BMSCs undergo a rapid loss of stemness after only a few passages. One of the most interesting aspects of this study was the integration of factors in the culture conditions, which to some extent, mimicked the in vivo microenvironmental niche of the BMSCs. A number of studies have successfully established that the cellular niche is not an inert tissue component but is of prime importance. The total sum of stimuli from the microenvironment underpins the complex interplay of regulatory mechanisms which control multiple functions in stem cells most importantly stem cell renewal. Therefore, well characterised factors which affect BMSCs characteristics, such as fibronectin (FN) coating, and morphogens such as FGF2 and BMP4, were incorporated into the cell culture conditions. The experimental set up was designed to provide insight into the expression pattern of the stem cell related transcription factors Sox2, cMyc and Oct4, in BMSCs with respect to passaging and changes in culture conditions. Induction of these pluripotency markers in somatic cells by retroviral transfection has been shown to confer pluripotency and an ESCs like state. Our study demonstrated that all treatments could transiently induce the expression of Sox2, cMyc and Oct4, and favourably affect the proliferation potential of BMSCs. The combined effect of these treatments was able to induce and retain the endogenous nuclear expression of stem cell transcription factors in BMSCs over an extended number of in vitro passages. Our results therefore suggest that the transient induction and manipulation of endogenous expression of transcription factors critical for stemness can be achieved by modulating the culture conditions; the benefit of which is to circumvent the need for genetic manipulations. In summary, this study has explored the role of BMSCs in the diseased state of osteoarthritis, by employing transcriptional profiling along with SI. In particular this study pioneered the use of primary cells for generating novel antibodies by SI. We established that somatic cells and BMSCs have a basal level of expression of pluripotency markers. Furthermore, our study indicates that intrinsic signalling mechanisms of BMSCs are intimately linked with extrinsic cues from the microenvironment and that these signals appear to be critical for retaining the expression of genes to maintain cell stemness in long term in vitro culture. This project provides a basis for developing an “artificial niche” required for reversion of commitment and maintenance of BMSC in their uncommitted homeostatic state.

The zygote and the very early cells are totipotent because they can produce a whole organism. Later, cells become pluripotent because they can differentiate into different subgroups of tissues. These cells can be extracted as embryonic stem cells (ESCs). Their pluripotent nature is due to the action of the pioneer transcription factors Oct4, Sox2 and Nanog. Multipotent or progenitor stem cells are present in adult organisms where they can differentiate into the various cells present in specific tissues. Differentiation depends on their microenvironment or niche. Differentiation of stem cells requires the silencing of the pluripotency genes and the activation of genes that are characteristic of different cell types. The genome of stem cells exhibits the same features of topological organization that are found in somatic cells. At the onset and throughout differentiation, the topological organization of the ESC genome changes, reflecting the changes in transcriptional activity that underlie the progression of pluripotent cells to multipotent progenitor cells and then to differentiated cells.

Four core transcription factors known to maintain the pluripotent state in embryonic stem cells (ESCs)—Oct4, Sox2, Klf4 and c-Myc—were used to induce pluripotent stem cells in adult-derived fibroblasts. Induced pluripotent stem cells (iPSCs), like ESCs, have less condensed and more transcriptionally active chromatin than differentiated cells. The number of genes with bivalent promoter marks increases during reprogramming, reflecting the switch of differentiation-specific active genes to an inactive, but poised, status. The levels of DNA methyl transferases and demethylases are increased, underlying the changes in the pattern of DNA methylation that occur late during reprogramming. The potential therapeutic applications of iPSCs include reprogramming a patient’s own cells to avoid the problem of rejection following injection to restore tissue or organ function. iPSCs derived from individuals at risk of developing late-onset neurological diseases could be differentiated in culture to predict the future occurrence of the disease. Caveats involve the fact that long-term culturing often results in genomic mutations that may, by chance, involve tumor suppressors or oncogenes.

Knee cartilage is a soft tissue having viscoelastic properties. Under cyclic loadings, viscoelastic materials dissipate mechanical loadings through heat generation. In knee cartilage, this heat might not be convected because of the tissue avascularity, resulting thus to a local temperature increase. As cells are sensitive to temperature, these thermo-mechanical phenomena of energy dissipation could influence their metabolism. The goal of this study is to evaluate the effect of thermogenesis on chondrogenic differentiation. First, we focused our work in quantifying the heat generated in cartilage as a result to deformation. On a cellular level, the effect of thermal alterations on cell metabolism was assessed looking at the gene expression of transcription factors involved in chondrogenesis. Hence, human chondro-progenitor cells were cultured at 33°C and 37°C for 48 h and 96 h. An up-regulation in mRNA expression levels of Sox9 and its co-activator PGC-1α has been observed. These results point to a thermal contribution to chondrogenic gene expression.

Generation of human induced pluripotent stem cells (hiPSCs) from fibroblasts and other somatic cells represents a highly promising strategy to produce auto- and allo-genic cell sources for therapeutic approaches as well as novel models of human development and disease1. Reprogramming protocols involve transduction of the Yamanaka factors Oct3/4, Sox2, Klf4, and c-Myc into the parental somatic cells, followed by culturing the transduced cells on mouse embryonic fibroblast (MEF) or human fibroblast feeder layers, and subsequent mechanical dissociation of pluripotent cell-like colonies for propagation on feeder layers1, 2. The presence of residual parental and feeder-layer cells introduces experimental variability, pathogenic contamination, and promotes immunogenicity3. Similar to human embryonic stem cells (hESCs), reprogrammed hiPSCs suffer from the unavoidable problem of spontaneous differentiation due to sub-optimal feeder cultures4, growth factors5, and the feeder-free substrate6. Spontaneously differentiated (SD)-hiPSCs display reduced pluripotency and often contaminate hiPSC cultures, resulting in overgrowth of cultures and compromising the quality of residual pluripotent stem cells5. Therefore, the ability to rapidly and efficiently isolate undifferentiated hiPSCs from the parental somatic cells, feeder-layer cells, and spontaneously differentiated cells is a crucial step that remains a bottleneck in all human pluripotent stem cell research.