Academic literature on the topic 'PI16'

IntroductionSocial cognition has been associated with functional outcome in patients with first episode psychosis (FEP). Social cognition has also been associated with neurocognition and cognitive reserve. Although cognitive reserve, neurocognitive functioning, social cognition, and functional outcome are related, the direction of their associations is not clear.ObjectivesThe aim of the study was to analyze the influence of social cognition as a mediator between cognitive reserve and cognitive domains on functioning in FEP both at baseline and at 2 years.MethodsThe sample of the study was composed of 282 FEP patients followed up for 2 years. To analyze whether social cognition mediates the influence of cognitive reserve and cognitive domains on functioning, a path analysis was performed. The statistical significance of any mediation effects was evaluated by bootstrap analysis.ResultsAt baseline, as neither cognitive reserve nor the cognitive domains studied were related to functioning, the conditions for mediation were not satisfied. Nevertheless, at 2 years of follow-up, social cognition acted as a mediator between cognitive reserve and functioning. Likewise, social cognition was a mediator between verbal memory and functional outcome. The results of the bootstrap analysis confirmed these significant mediations (95% bootstrapped CI (−10.215 to −0.337) and (−4.731 to −0.605) respectively).ConclusionsCognitive reserve and neurocognition are related to functioning, and social cognition mediates in this relationship.DisclosureThis work was supported by the Carlos III Institute of Health and European Fund for Regional Development (PI08/1213, PI11/ 01977, PI14/01900, PI08/01026, PI11/02831, PI14/01621, PI08/1161, PI16/ 00359, PI16/01164, PI18/00805), the Basque Foundation for He

Abstract T helper (Th) cells play a major role in protecting the body against pathogens. Any imbalance in Th cell subsets could lead to autoimmune and inflammatory diseases. Peptidase inhibitor 16 (PI16), also known as prostate secretory protein of 94 amino acid - binding protein, was recently discovered to be expressed on memory regulatory T cells. This study investigates the expression and function of PI16 on Th cells. In healthy adults, 5-25% of CD4+ Th cells express PI16 with over 90% showing a memory phenotype. PI16+ Th cells have an increased expression of chemokine receptors CCR4 and CCR6 compared with PI16- Th cells. Transwell migration assays showed that more PI16+ Th cells migrated towards the CCR4 and CCR6 ligands (CCL17 and CCL20) compared with PI16- Th cells. After 7 day stimulation using CD3 / CD28 beads, PI16+ Th cells produce more IL-17A and less IFN-g compared with PI16- Th cells. PI16+ Th cells also have a higher expression of ROR-gt compared to PI16- Th cells. Furthermore, in comparison to PI16- Th cells, PI16+ Th cells have an increased proliferative potential and are less responsive to suppression by Treg. The memory phenotype of PI16+ Th cells, the high expression of Th17-like chemokine receptors, increased ROR-gt expression and high production of IL-17A suggest an active role of PI16+ Th cells at the site of infection or inflammation. Further studies are ongoing to understand the functional role of PI16 on Th cells in autoimmune and inflammatory diseases.

Chronic pain is a major clinical problem of which the mechanisms are incompletely understood. Here, we describe the concept that PI16, a protein of unknown function mainly produced by fibroblasts, controls neuropathic pain. The spared nerve injury (SNI) model of neuropathic pain increases PI16 protein levels in fibroblasts in dorsal root ganglia (DRG) meninges and in the epi/perineurium of the sciatic nerve. We did not detect PI16 expression in neurons or glia in spinal cord, DRG, and nerve. Mice deficient in PI16 are protected against neuropathic pain. In vitro, PI16 promotes transendothelial leukocyte migration. In vivo, Pi16−/− mice show reduced endothelial barrier permeability, lower leukocyte infiltration and reduced activation of the endothelial barrier regulator MLCK, and reduced phosphorylation of its substrate MLC2 in response to SNI. In summary, our findings support a model in which PI16 promotes neuropathic pain by mediating a cross-talk between fibroblasts and the endothelial barrier leading to barrier opening, cellular influx, and increased pain. Its key role in neuropathic pain and its limited cellular and tissue distribution makes PI16 an attractive target for pain management.

Background:Regulatory T cells (Tregs) play an essential role in maintaining self-tolerance and immune homeostasis. Abnormalities in the quantity or function of Treg cells are believed in RA patients, contributing to the inability to suppress autoimmunity and proinflammatory cytokines. Forkhead box P3 (Foxp3) is a crucial transcription factor for the development and differentiation of Tregs. How Tregs lose Foxp3 expression under inflammatory milieu remains largely unknown. Peptidase inhibitor 16 (PI16) is a member of the CAP (Cysteine-rich secretory proteins, Antigen 5, and Pathogenesis-related 1) protein family and its function are largely poor understood. In a genome-wide expression profiling study for identifying human Foxp3 target genes revealed PI16 was expressed on the cell surface of >80% of resting human CD25+ Foxp3+ Tregs. In the inflamed joint of juvenile idiopathic arthritis revealed a low number of PI16+ Tregs but high number of Th17 cells. However, little is known the function role of PI16 on Tregs or on RA development.Objectives:To investigate the role of peptidase inhibitor 16 (PI16) on the key T regulatory (Tregs) cells transcription factor Foxp3 expression and on the development of autoimmune arthritis.Methods:The expression of PI16 in blood, synovial fluid, inflamed joints were examined in Rheumatoid arthritis (RA) patients and in arthritic mice. Arthritis symptom, histological features and Foxp3 expression in PI16 transgenic (PI16Tg) arthritic mice were examined. Posttranslational mechanisms on PI16-mediated Foxp3 expression were analyzed. The specific role PI16 on Foxp3 expression was validated in conditional knockout (KO) mice.Results:The expression of PI16 was significantly increased in PBMC, serum, synovial tissue from RA patients or arthritic mice compared with controls. PI16Tg arthritic mice exhibited obvious inflammation, synovial hyperplasia and articular cartilage destruction in the joints compared with those in wild-type mice (WT) arthritic mice.Foxp3 is downregulated in splenic T cells and synovial tissue from PI16Tg arthritic mice. Naïve T cells derived from PI16Tg arthritic mice showed the decreased capacity to differentiate into Tregs. Polycomb-group (PcG) proteins complex molecule of Bmi-1 was significant increase in Tregs and joint tissue from PI16Tg arthritic mice. A direct interaction between 1-95AA domains of PI16 and 169 and 436 domains of Bmi-1 in Tregs promoter was observed. The binding of PI16 with Bmi-1 in the Foxp3 promoter inhibit the K48-linked polyubiquitin degradation of Bmi-1 at lysine site 72 and 153 region, which prompts the repressive histone modification of H3K27me3 and H2AK119ub, and inhibits the active histone modification of H3K4me3. Furthermore, conditional knockout of PI16 in Tregs retarded Foxp3 loss and blunted disease progression in experimental arthritis.Conclusion:PI16 represses Foxp3 expression by mediating histone modification via inhibiting K48-linked polyubiquitin degradation of Bmi-1 in Foxp3 promoter, contributing to disease progression in arthritic mice.Disclosure of Interests:None declared.

Background. It has been reported that there may be a potential link between hernia and dementia. However, the exact mechanisms of their association have not been established. This study is aimed at constructing miRNA-mRNA networks to elucidate on the potential link between dementia and hernia. Methods. Gene expression profiles for dementia, herniation, and skeletal muscle were downloaded from the GEO database after which differentially expressed mRNAs and miRNAs were obtained. In addition, fascia tissue samples were obtained during surgery. A total of 41 patients were recruited in this study, and expression levels of candidate genes were examined using quantitative RT-PCR. Luciferase reporter gene assays were used to identify potential miRNA-mRNA regulatory pathways. Results. Differentially expressed mRNAs and miRNAs were screened. A potential miRNA-mRNA network revealing the crosstalk mechanism between herniation and dementia was identified. Single cell analysis revealed that PI16 was highly enriched in adipose tissues, skeletal muscles, and in the skin. GSEA enrichment analysis showed that PI16 is involved in adipose metabolism, muscle functions, and energy metabolism. In clinical samples, PI16 was found to be upregulated in hernia, while miR-4451 was found to be downregulated. The luciferase reporter gene assay revealed that downregulation of circulating miR-4451 may be responsible for the upregulated PI16 expression in hernia sacs. Conclusions. We constructed an miRNA-mRNA network that shows the potential association between dementia and hernia. We also found that miR-4451 regulates the PI16 expression, which may be a key target and biomarker for hernia pathogenesis and dementia crosstalk.

Objective.Early recognition and treatment of juvenile idiopathic arthritis (JIA) can prevent joint damage and minimize side effects of medication. The balance between proinflammatory and antiinflammatory mechanisms is known to be important in JIA, and we therefore investigated T cell subsets including Th cells, autoaggressive Th17 cells, and regulatory T cells (Treg), including a novel Treg subset in peripheral blood (PB) and synovial fluid (SF) of patients with JIA.Methods.Fifty children with JIA were enrolled in our study. Frequency, phenotype, and function of T lymphocytes in PB and SF were characterized using flow cytometry. Migration capabilities of PB and SF cells were compared.Results.Synovial T cells showed different phenotype and function compared with PB T cells, with an increased proportion of memory T cells, expression of CCR4, CCR5, CXCR3, interleukin 23R, and an increased ratio of Th17 to Treg. Although Treg were increased in SF compared with the PB, we found a significant decrease in the numbers of peptidase inhibitor 16 (PI16)+ Treg in active joints compared with peripheral blood. Coexpression of CCR4 and CCR6 was reduced on PI16+ Treg in PB and SF of patients with JIA compared with healthy children, however the ability of these cells to migrate toward their ligands was unaffected.Conclusion.This is a comprehensive characterization of novel PI16+ Treg and Th17 cells in matched blood and synovial fluid samples of patients with JIA. Despite an increased number of Treg within the inflamed joint, lower numbers of PI16+ Treg but high numbers of Th17 cells might contribute to the inability to control disease.

A total of 99 isolates of rice blast (Pyricularia oryzae Cavara) were collected from 2010 to 2015 from four regions in Kenya: Kirinyaga County and Embu County, Kisumu County, Tana River County, and Mombasa County. The pathogenicities of these isolates were clarified based on the reaction patterns of Lijiangxintuanheigu and differential varieties (DVs) targeting 23 resistance genes. The frequency of virulent isolates was high for DVs for Pib, Pia, Pii, Pi3, Pi5(t), Pik-s, Pik-m, Pi1, Pik-h, Pik, Pik-p, Pi7(t), Pi19(t), and Pi20(t); low for DVs for Pish, Pi9(t), Piz-5, and Piz-t; and intermediate for the remaining DVs for Pit, Piz, Pita-2, Pita, and Pi12(t). These blast isolates were classified into three cluster groups: Ia, Ib, and II. The frequencies of virulent isolates to DVs for Pit, Pii, Pik-m, Pi1, Pik-h, Pik, Pik-p, Pi7(t), Piz, and Pi12(t) differed markedly between clusters I and II, and those of DVs for Pib, Pit, Pia, Pi3, Pita-2, Pita, and Pi20(t) differed between Ia and Ib. The frequencies of cluster groups in the four geographical regions were different. A total of 62 races were found, with 19 blast isolates categorized into one race (U63-i7-k177-z00-ta003), whereas the other races included only some isolates in each.

Abstract The cysteine-rich secretory proteins, antigen 5, and pathogenesis-related 1 proteins (CAP) superfamily members are found in a remarkable range of organisms spanning each of the animal kingdoms. Within humans and mice, there are 31 and 33 individual family members, respectively, and although many are poorly characterized, the majority show a notable expression bias to the reproductive tract and immune tissues or are deregulated in cancers. CAP superfamily proteins are most often secreted and have an extracellular endocrine or paracrine function and are involved in processes including the regulation of extracellular matrix and branching morphogenesis, potentially as either proteases or protease inhibitors; in ion channel regulation in fertility; as tumor suppressor or prooncogenic genes in tissues including the prostate; and in cell-cell adhesion during fertilization. This review describes mammalian CAP superfamily gene expression profiles, phylogenetic relationships, protein structural properties, and biological functions, and it draws into focus their potential role in health and disease. The nine subfamilies of the mammalian CAP superfamily include: the human glioma pathogenesis-related 1 (GLIPR1), Golgi associated pathogenesis related-1 (GAPR1) proteins, peptidase inhibitor 15 (PI15), peptidase inhibitor 16 (PI16), cysteine-rich secretory proteins (CRISPs), CRISP LCCL domain containing 1 (CRISPLD1), CRISP LCCL domain containing 2 (CRISPLD2), mannose receptor like and the R3H domain containing like proteins. We conclude that overall protein structural conservation within the CAP superfamily results in fundamentally similar functions for the CAP domain in all members, yet the diversity outside of this core region dramatically alters target specificity and, therefore, the biological consequences.

In total, 310 rice blast (Pyricularia oryzae Cavara) isolates from Japan showed wide variation in virulence. Virulence on rice (Oryza sativa L.) differential varieties (DV) harboring resistance genes Pish, Pia, Pii, Pi3, Pi5(t), Pik-s, and Pi19(t) ranged from 82.9 to 100.0%. In contrast, virulence on DV possessing Pib, Pit, Pik-m, Pi1, Pik-h, Pik, Pik-p, Pi7(t), Pi9(t), Piz, Piz-5, Piz-t, Pita-2, Pita, Pi12(t), and Pi20(t) ranged from 0 to 21.6%. Cluster analysis using the reaction patterns of the DV classified isolates into three groups: I, virulent to Pik, Pik-h, Pik-p, Pik-m, Pi1, and Pi7(t); IIa, avirulent to the preceding 6 genes and virulent to Pia, Pii, Pi3, and Pi5(t); and IIb, avirulent to all 10 genes. Group I was limited to northern Japan and group IIb to central Japan, while group IIa was distributed throughout Japan. We estimate that group IIa represents the original population and that groups I and IIb arose from it through minor changes in pathogenicity. We classified these isolates into 123 races by a new designation system and conclude that the rice blast races in Japan are less diverse than previously thought.

CD4 T cells, a major component of the immune system, are a heterogeneous population comprising cells with known and unknown function in both health and disease. Biomarkers that identify pathogenic T cell subsets enable early diagnosis and may also provide leads for therapeutic intervention. Peptidase inhibitor 16 (PI16), a recently discovered biomarker by the Barry lab, for a functionally distinct subset of regulatory T cells, is also expressed in T helper cells. However, the characteristics of PI16 expressing T helper cells have not been previously studied. This thesis investigates the molecular and functional characteristics of PI16+ T helper (Th) cells in health and disease. A high proportion of PI16+ Th cells express the chemokine receptors CCR4 and CCR6 in comparison with PI16- Th cells, indicating ability to respond to chemotactic stimuli, which was confirmed by in-vitro migration assays. Upon in-vitro stimulation, PI16+ Th cells express high levels of the Th17 transcription factor, ROR-γt, and produce more pro-inflammatory cytokines, including IL-17A, TNF, but less IFN-γ in comparison with PI16- Th cells. In the steady state, PI16+ Th cells express high levels of FAS receptor and low levels of CD38 and CXCR5, indicating a mature phenotype. Microarray analysis showed 649 genes were differentially expressed between PI16+ and PI16- Th cells and pathway analysis of the gene profile of PI16+ Th cells indicates a potential role in cell-mediated immune response, migration and inflammatory response. Intriguingly, nearly all PI16+ Th cells are memory (CD45RO+) cells, but not all memory cells are PI16+. Hence, PI16- cells are a mixture of CD45RA+ and CD45RO+. In order to exclude the possibility that the distinct characteristics of PI16+ Th cells are simply due to their differing memory status, this study further compares the functional and phenotypical difference between purified PI16+ memory and PI16- memory Th cells. PI16+ cells may mimic the properties of long-term resting memory T cells by their high expression of Integrin β1, Hepatic leukemia factor and Clusterin and low expression of Tyrosine kinase and CCL5. In addition, high expression of histamine H₄ receptor, Angiotensin converting enzyme 1 and Galectin-1 in PI16+ cells in comparison with PI16- memory Th cells may indicate their potential role in inflammation. Intracellular phosphoprotein analysis showed altered kinetics of STAT signalling by PI16+ cells in response to cytokine stimuli, compared with PI16- cells. Upon stimulation, PI16+ cells secrete more IL-2 than PI16- cells, indicating a potential autocrine driven proliferation status, which was confirmed by proliferation assay. However, PI16+ Th are more apoptotic on the one hand but resistant to suppression by Treg compared with PI16- mem Th cells on the other hand. A chemokine receptor profiling based method to segregate Th1, Th2, Th17 and Th22 subsets indicates, all the subsets express PI16 at varying proportions, but the Th22 subset almost uniformly expresses PI16. In order to further investigate the role of PI16+ Th cells in disease, a suite of pilot clinical studies were performed including rheumatoid arthritis (RA), juvenile idiopathic arthritis, scleroderma, asthma, chronic sinusitis and type I diabetes. The preliminary data indicate that in the peripheral blood of sinusitis and RA patients, the proportion of PI16+ Th cells were higher compared with healthy controls. In the peripheral blood of RA and scleroderma patients, higher numbers of CD45RA+PI16+ Th cells were present while these are almost undetectable in healthy control, which may indicate the peripheral expansion of this subset. In conclusion, PI16 may be a biomarker for long-term memory Th cells with potent effector functions. Preliminary clinical studies on the role of PI16+ Th cells in autoimmune / inflammatory diseases provide promising first data warranting further investigation on the functional role of the PI16+ CD4+ CD25- cells to determine whether or not they represent a novel lineage.
Thesis (Ph.D.) (Research by Publication) -- University of Adelaide, School of Paediatrics and Reproductive Health, 2015.

Tese de doutoramento em Biologia (Biologia Molecular), apresentada à Universidade de Lisboa através da Faculdade de Ciências, 2008
A proteína PIN6 é um dos membros menos caracterizados da família de proteínas PIN, associadas ao transporte de auxina em Arabidopsis thaliana. Nesta planta modelo, o transporte polar auxínico tem sido associado a diversos processos fisiológicos. Por exemplo, o movimento acropetal de IAA, do caule para a raíz, tem sido implicado no desenvolvimento de raízes laterais, enquanto que o movimento basipetal de IAA, do ápice radicular para a junção caule-raíz, tem sido associado à resposta à gravidade. As proteínas PIN desempenham um papel crucial no transporte polar auxínico e desta forma medeiam o estabelecimento e manutenção de meristemas, a iniciação e posicionamento de órgãos laterais, a formação do tecido vascular e as diversas formas de tropismo. Neste trabalho procedeu-se ao estudo da função do gene PIN6 recorrendo a diversas técnicas de engenharia genética e de biologia molecular. O gene PIN6 apresenta níveis de expressão génica relativamente baixos e específicos, sendo detectado apenas em determinadas células e em etapas específicas do desenvolvimento vegetal. O PIN6 é expresso durante a formação de raízes laterais desde a fase de iniciação da raíz, quando as células do periciclo, nos vasos condutores, são activadas para entrarem em divisão celular, até fases mais tardias, como a da emergência da raíz lateral. Na fase de indução de raízes laterais o gene PIN6 encontra-se a marcar as células fundadoras da futura raíz lateral no periciclo. Numa fase posterior, de emergência das raízes laterais, PIN6 é expresso nas margens da raíz lateral, na zona de contacto com a raíz principal, formando uma estrutura em forma de anel. O PIN6 está, ainda, presente no meristema apical caulinar, em domínios restritos localizados sob os locais de formação de novos órgãos e nos vasos condutores dos mesmos. Este gene parece estar maioritariamente relaccionado com o desenvolvimento de novos órgãos laterais ao nível dos meristemas. Os avanços recentes ao nível da Biologia disponibilizaram uma elevada diversidade de estratégias para caracterização funcional de um determinado gene ou família de genes. O recurso a técnicas de genética reversa permite a caracterização funcional de um gene pela determinação do efeitos causados pela sua ausência. Para a caracterização funcional do PIN6 procedeu-se a uma pesquisa de alelos provenientes de colecções de mutantes com inserções de T-DNA. Foram ainda criadas linhas transgénicas com redução dos níveis de expressão do PIN6. Para o efeito, recorreu-se à estratégia de RNA de interferência (RNAi). Os fenótipos das diferentes linhas foram analisados em diversas condições de crescimento. As mutações resultaram em taxas de crescimento da raíz primária superiores e num aumento da produção de raízes laterais em relação às plantas de fenótipo selvagem. Tendo em conta esse fenótipo, a proteína PIN6 é, na generalidade, repressora dos processos de crescimento. O fenótipo dos mutantes pin6 é, ainda, afectado pelo fotoperíodo, uma vez que os fenótipos observados nas plantas crescidas em condições de dia longo foram mais drásticos do que os patentes nas crescidas em presença de luz contínua. Para avaliar uma possível regulação ao nível da percepção da luz, as plantas foram crescidas sob luz contínua com radiações de diferentes comprimento de onda: branco, azul, vermelho, vermelho-longínquo e UV-B. Os mutantes pin6 apresentam maior de-estiolação do hipocótilo sob radiação vermelho-longínqua e UV-B, tendo sido observada uma indução da expressão de PIN6, o que sugere uma interacção, se bem que indirecta, com pigmentos receptores de luz, dos quais se destaca o fitocromo A. Adicionalmente, os mutantes germinaram mais cedo e fazem a transição meristemática da fase vegetativa para a fase reprodutiva antes do fenótipo selvagem, produzindo menos folhas roseta e menos ramificações secundárias nos caules e nas inflorescências. Estes resultados apontam para uma relação estrita entre o PIN6 e genes de identidade dos meristemas vegetativo e floral. Os mutantes pin6 são ainda hipergravitrópicos, sugerindo um papel para PIN6 na percepção da gravidade, provavelmente em conjunto com PIN2. A proteína PIN2 foi já caracterizada como envolvida na resposta à gravidade e o seu gene é expresso juntamente com o PIN6 nos tecidos na raíz. Os níveis de expressão destes dois genes são afectados por alguns factores comuns. Actualmente está disponível uma vasta gama de informação proveniente de experiências de análise de transcritos a larga escala e de pesquisa in vitro de parceiros de interacção, especialmente em Arabidopsis thaliana. Cada vez mais se torna necessário recorrer a estratégias de biologia de sistemas que permitam análises transversais dos resultados obtidos, cruzando dados de fontes diversas para obtenção de informações sobre determinados genes ou processos de interesse. Uma análise in silico dos dados existentes forneceu informação adicional necessária à caracterização do gene PIN6 no que diz respeito à compreensão da sua função e dos mecanismos de regulação que o regem nos processos de desenvolvimento vegetal mencionados, nomeadamente no que diz respeito às respostas a outras hormonas vegetais. Dessa análise concluiu-se que a expressão de PIN6 é afectada a diversos níveis, nomeadamente factores de transcrição para os quais existem elementos reguladores na sequência do promotor de PIN6 e que estão envolvidos na iniciação de fases do desenvolvimento. A nível da iniciação das germinação e desenvolvimento foliar, o PIN6 parece ser induzido pela diminuição dos níveis de LEC1, um factor de transcrição envolvido na dormência e em fases embrionárias do desenvolvimento foliar. MAX4, membro de uma família de genes envolvida na ramificação do caule, parece ser também um repressor da expressão do PIN6, uma relação já descrita para outros genes MAX e PIN. FLC e VIP estão envolvidos no controlo temporal da floração e percepção da vernalização, respectivamente, e interagem um com o outro para promover a iniciação floral estando, possivelmente, envolvidos no controlo da expressão do PIN6. Ao nível da formação de raízes laterais, a proteína PIN6 pode interagir com MDR4, uma proteína envolvida no transporte basipetal auxínico. A sobre-expressão de E2Fa-DPa, um factor de transcrição envolvido na divisão celular e ligado à resposta auxínica, resulta na repressão do PIN6. Adicionalmente, estão presentes no promotor do PIN6 elementos reguladores do ciclo celular, bem como da síntese de componentes da parede celular, sugerindo que a função do PIN6 nas células meristemáticas ocorre principalmente ao nível da divisão celular. As auxinas aumentam os níveis de transcriptos do PIN6 e induzem a sua expressão ectópica em tecidos da raíz. Há evidências desta regulação ocorrer através da via que envolve TIR1-Aux/IAA-ARF e que corresponde à degradação dos repressores Aux/IAAs dependente do proteassoma, libertando os factores de transcrição ARF que, por sua vez, induzem possivelmente a expressão génica do PIN6 . Constata-se a existência de redundância ao nível dos membros da família de proteínas PIN: no mutante pin1 o domínio de expressão do PIN6 expande-se para filas adicionais de células companheiras dos vasos condutores, de modo a equiparar a falta de proteína PIN1 nessas células. Com este trabalho pretendeu-se sugerir hipóteses explicativas dos mecanismos pelos quais PIN6 faz a ligação entre o transporte auxínico e os processos de desenvolvimento em que esta proteína está envolvida, nomeadamente na transição de fase, no estabelecimento e manutenção do meristema apical caulinar, na formação de novos órgãos, folhas e raízes laterais, e na resposta gravirópica. Neste trabalho propõem-se, ainda, estratégias para abordagem dos diferentes pontos que ainda carecem de esclarecimento.
PIN6, a member of the PIN protein family of auxin transporters, is expressed in relatively low levels and in particular cells at distinct time points. This gene seems to be mainly involved with new lateral organ development. It is expressed in lateral roots, since early stages when pericycle cells are activated for cell division, and in the shoot apical meristem, in restricted domains directly below sites of new organ formation. Screening for T-DNA insertional mutant alleles and generation of knock- down transgenic lines for PIN6 provided the tools to characterize this gene's function. Phenotypes of those lines were analyzed under different growth conditions and included faster growth rates, longer roots and production of more lateral roots. PIN6 is therefore likely to be a negative regulator of overall growth processes. PIN6 phenotype is regulated by photoperiodism, as phenotypes were more drastic under specific photoperiodic conditions. Furthermore, pin6 mutants germinate and make meristem transition from vegetative to reproductive phase earlier than WT, producing less rosette leaves, less secondary branches and inflorescence stems. These results imply a tight regulation between PIN6 and both vegetative and floral meristem identity genes. In addition, pin6 mutants are hypergravitropic, proposing a role for PIN6 in gravity perception, probably in a concerted fashion with PIN2. Auxin upregulates PIN6 expression levels and induces its ectopic expression in additional root tissues. A certain degree of redundancy exists among PIN protein family members. In fact, in the pin1 mutant PIN6 protein localizes to additional cell files, thus compensating for the absence of PIN1. An additional analysis of in silico available data from microarray experiments provided extra information required to better understand PIN6 function and its regulation, namely by other hormones. Explanations regarding the mechanisms by which PIN6 links auxin transport to developmental processes as phase transition, new lateral organ emergence and gravitropism, are proposed.