Academic literature on the topic 'Centriole elimination'

An important feature of fertilization is the asymmetric inheritance of centrioles. In most species it is the sperm that contributes the initial centriole, which builds the first centrosome that is essential for early development. However, given that centrioles are thought to be exceptionally stable structures, the mechanism behind centriole disappearance in the female germ line remains elusive and paradoxical. We elucidated a program for centriole maintenance in fruit flies, led by Polo kinase and the pericentriolar matrix (PCM): The PCM is down-regulated in the female germ line during oogenesis, which results in centriole loss. Perturbing this program prevents centriole loss, leading to abnormal meiotic and mitotic divisions, and thus to female sterility. This mechanism challenges the view that centrioles are intrinsically stable structures and reveals general functions for Polo kinase and the PCM in centriole maintenance. We propose that regulation of this maintenance program is essential for successful sexual reproduction and defines centriole life span in different tissues in homeostasis and disease, thereby shaping the cytoskeleton.

Centriole elimination is an essential process that occurs in female meiosis of metazoa to reset centriole number in the zygote at fertilization. How centrioles are eliminated remains poorly understood. Here we visualize the entire elimination process live in starfish oocytes. Using specific fluorescent markers, we demonstrate that the two older, mother centrioles are selectively removed from the oocyte by extrusion into polar bodies. We show that this requires specific positioning of the second meiotic spindle, achieved by dynein-driven transport, and anchorage of the mother centriole to the plasma membrane via mother-specific appendages. In contrast, the single daughter centriole remaining in the egg is eliminated before the first embryonic cleavage. We demonstrate that these distinct elimination mechanisms are necessary because if mother centrioles are artificially retained, they cannot be inactivated, resulting in multipolar zygotic spindles. Thus, our findings reveal a dual mechanism to eliminate centrioles: mothers are physically removed, whereas daughters are eliminated in the cytoplasm, preparing the egg for fertilization.

Male meiosis in Trichosia pubescens (Sciaridae) was investigated by means of serial section electron microscopy and immunofluorescence light microscopy. From earlier studies of another sciarid fly, Sciara coprophila (Phillips (1967) J. Cell. Biol. 33, 73–92), it is known that the spindle poles in sciarid spermatogonia are characterized by pairs of ‘giant centrioles’, ring-shaped organelles composed of large numbers of singlet microtubules. In the present study spermatocytes in early prophase of Trichosia were found to possess single giant centrioles at opposite sides of the nucleus. The obvious reduction in centriole number from the spermatogonial to the spermatocyte stage is suggested to be the result of a suppression of daughter centriole formation. In late prophase, a large aster is developed around the centriole at one pole. At the opposite pole no comparable aster is formed. Instead, a number of irregular centriolar components appear in this region, a process that is understood to be a degeneration of the polar organelle. The components of the degenerate pole migrate into a cytoplasmic protrusion (‘bud’), which later is also utilized for the elimination of paternal chromosomes. The existence of only one functional polar centre is the reason for the formation of a monopolar monocentric spindle in first meiotic division, which in turn is one of the prerequisites for the elimination of paternal chromosomes. While the set of maternal and L chromosomes orientates and probably moves towards the pole, paternal chromosomes seem to be unable to contact the pole, possibly due to an inactivation of their kinetochores. Retrograde (‘away from the pole’) chromosome motion not involving kinetochores is assumed. Eventually, paternal chromosomes move into the pole-distal bud and are eliminated by casting off, together with the components of the degenerate polar organelle. Chromosome elimination can be delayed until the second meiotic division. The spindle of the second meiotic division is bipolar and monocentric. One spindle pole is marked by the polar centre of first division. The opposite spindle apex is devoid of a polar centre. It is assumed that spindle bipolarity in the second division is induced by the amphi-orientated chromosomes themselves. The maternal and L chromosome set (except the non-disjunctional X chromosome, which is found near the polar centre) congress in a metaphase plate, divide and segregate. Of the two daughter nuclei resulting from the second meiotic division, the one containing the X chromatids is retained as the nucleus of the future spermatozoon. The other nucleus becomes again eliminated within a second cytoplasmic bud.

ABSTRACTSteroidogenic factor 1 (SF-1 or NR5A1) is a nuclear receptor that controls adrenogenital cell growth and differentiation. Adrenogenital primordial cells fromSF-1knockout mice die of apoptosis, but the mechanism by which SF-1 regulates cell survival is not entirely clear. Besides functioning in the nucleus, SF-1 also resides in the centrosome and controls centrosome homeostasis. Here, we show that SF-1 restricts centrosome overduplication by inhibiting aberrant activation of DNA-dependent protein kinase (DNA-PK) in the centrosome. SF-1 was found to be associated with Ku70/Ku80 only in the centrosome, sequestering them from the catalytic subunit of DNA-PK (DNA-PKcs). In the absence of SF-1, DNA-PKcs was recruited to the centrosome and activated, causing aberrant activation of centrosomal Akt and cyclin-dependent kinase 2 (CDK2)/cyclin A and leading to centrosome overduplication. Centrosome overduplication caused by SF-1 depletion was averted by the elimination of DNA-PKcs, Ku70/80, or cyclin A or by the inhibition of CDK2 or Akt. In the nucleus, SF-1 did not interact with Ku70/80, and SF-1 depletion did not activate a nuclear DNA damage response. Centriole biogenesis was also unaffected. Thus, centrosomal DNA-PK signaling triggers centrosome overduplication, and this centrosomal event, but not the nuclear DNA damage response, is controlled by SF-1.

In many animals, the bipolar spindle of the first zygotic division is established after the contribution of centrioles by the sperm at fertilization. To avoid the formation of a multipolar spindle in the zygote, centrosomes are eliminated during oogenesis in most organisms, although the mechanism of this selective elimination is poorly understood. We show that cki-2, a Caenorhabditis elegans cyclin-dependent kinase (Cdk) inhibitor, is required for their appropriate elimination during oogenesis. In the absence of cki-2, embryos have supernumerary centrosomes and form multipolar spindles that result in severe aneuploidy after anaphase of the first division. Moreover, we demonstrate that this defect can be suppressed by reducing cyclin E or Cdk2 levels. This implies that the proper regulation of a cyclin E–Cdk complex by cki-2 is required for the elimination of the centrosome that occurs before or during oogenesis to ensure the assembly of a bipolar spindle in the C. elegans zygote.

Spermiogenesis and sperm ultrastructure were analyzed in two species of characids with different modes of fertilization: externally fertilizing Hemigrammus erythrozonus and inseminating Corynopoma riisei. Spermiogenesis in H. erythrozonus is characterized by lateral development of the flagellum, nuclear rotation, formation of a shallow nuclear fossa, condensation of the chromatin by elimination of the electron-lucent area from the peripheral region of the nucleus, and renewal of the nuclear membrane. Multilammelated membrane and multivesicular bodies were also observed during elimination of the excess cytoplasm. The spermatozoon exhibits characters typical of "aquasperm," i.e. a spherical head containing a spherical nucleus with highly condensed chromatin, several small mitochondria located at the base of the nucleus within a cytoplasmic collar that extends into a long cytoplasmic sleeve surrounding the anterior part of the single flagellum, which is contained within a cytoplasmic canal. The flagellum lacks fins. The proximal and distal centrioles are nearly parallel to one another, with the anterior tips of both located within shallow nuclear fossae. Spermiogenesis in C. riisei is characterized by nuclear elongation alongside the forming flagellum, formation of an elongate cytoplasmic canal, displacement and elongation of the mitochondria, and uniform condensation of chromatin throughout the nucleus through enlargement of the diameter of the chromatin granules. The spermatozoon has an elongate nucleus with two elongate mitochondria localized to one side. Mitochondria are also located posterior to the nucleus forming a mitochondrial region. The single flagellum, which lacks fins, is lateral to the nucleus and initially contained within the greatly elongate cytoplasmic canal before exiting the canal at its posterior terminus. The spermatozoon of C. riisei exhibits several characters typical of "introsperm," such as an elongate nucleus and midpiece (mitochondrial region). The nuclear chromatin in the spermatozoon remains "flocculent" and is never as condensed as that seen in many characid sperm. Differences in spermiogenesis between externally fertilizing and inseminating characids are discussed.

Analysis of glycan chains of glycoconjugates is difficult because of their considerable variety. Despite this, several functional roles for these glycans have been reported. N-Glycans are oligosaccharides linked to asparagine residues of proteins. They are synthesised in the endoplasmic reticulum (ER) in a unique way, and later modified in both the ER and Golgi apparatus, developing different oligosaccharide chains. An essential role for complex N-glycans in mammalian spermatogenesis has been reported. The aim of the present study was to analyse the N-glycans of the Xenopus laevis testis by means of lectin histochemistry. Five lectins were used that specifically recognise mannose-containing and complex glycans, namely Galanthus nivalis agglutinin (GNA) from snowdrops, concanavalin A (Con A) from the Jack bean, Lens culinaris agglutinin (LCA) from lentils and Phaseolus vulgaris erythroagglutinin (PHA-E) and P. vulgaris leukoagglutinin (PHA-L) from the common bean. GNA and Con A labelled the interstitium and most of the germ cell types, whereas LCA and PHA-E showed affinity only for the interstitium. A granular cytoplasmic region was labelled in spermatogonia and spermatocytes by GNA and PHA-L, whereas GNA and LCA labelled a spermatid region that is probably associated with the centriolar basal body of the nascent flagellum. There was no specific labelling in the acrosome. Some unexpected results were found when deglycosylative pretreatments were used: pre-incubation of tissue sections with peptide N glycosidase F, which removes N-linked glycans, reduced or removed labelling with most lectins, as expected. However, after this pretreatment, the intensity of labelling remained or increased for Con A in the follicle (Sertoli) and post-meiotic germ cells. The β-elimination procedure, which removes O-linked glycans, revealed new labelling patterns with GNA, LCA and PHA-L, suggesting that some N-glycans were masked by O-glycans, and thus they became accessible to these lectins only after removal of the O-linked oligosaccharides. The functional role of the glycan chains identified could be related to the role of N-glycans involved in mammalian spermatogenesis reported previously.

Dissertation presented to obtain the Ph.D degree in Cellular Biology
The centriole is a Eukaryotic organelle involved in a variety of processes. Within the cytoplasm the centriole is part of the centrosome, the major microtubule (MT) organizing center in animal cells. The centrosome is involved in the regulation of cell motility and polarity in interphase and the organization of the mitotic spindle in mitosis. Each centrosome is composed of two centrioles surrounded by a protein-rich matrix, the pericentriolar material (PCM) (reviewed by Bettencourt-Dias and Glover, 2007) .(...)

The centrosomes play an essential role in cell and tissue homeostasis, therefore, their structure, function, and number are highly regulated to ensure natural organisms development through the assembly of a multiplicity of protein complexes. Since the organization and integrity of the centrosome depend on its centrioles and pericentriolar material (PCM), understanding the dynamics of these organelles is crucial to decipher the centrosome behaviour. To date, we have a fairly detailed knowledge of the centriole composition and structure and also of the process of duplication and centrosomal maturation. Something is understood about the process of centriole elimination during gametogenesis, but very little is known about how centrioles are eliminated in post-mitotic differentiated cells. During the development of the Drosophila eye, the centrioles of the differentiating retinal cells do not recruit γ-Tubulin, suggesting that they are unable to organize functional microtubule-organizing centers (MTOCs). Consistent with this hypothesis, this study shows that in Drosophila third instar larvae Cnn and Spd-2, proteins that allow γ-Tubulin recruitment, and DPlp, which is involved in the organization of the pericentriolar material, are not accumulated by centrioles of eye imaginal disc cells. Despite the loss of these essential components of the pericentriolar material, the centrioles are structurally intact and can recruit Asl and ANA-1. Usually, the accumulation of Asl and ANA-1 allows the daughter centrioles to acquire the motherhood condition. Indeed, mother centrioles accumulate properly Plk-4; however, they are not able to duplicate. These findings show that, in this model, the accumulation of Plk-4 is not sufficient to allow centriole duplication. During the progression of pupal development, the centriole number progressively decreases, and structural defects can be observed. These phenotypes suggest that during Drosophila eye development centriole elimination begins with the loss of the structural integrity, rather than with the PCM reduction as occurs in other models. Furthermore, Asl, ANA-1 and Sas-4 are still detectable, indicating that these proteins by themselves are not able to ensure the maintenance of centriole integrity. Among the essential cellular functions played by centrioles, there is their ability to act as basal bodies to nucleate the axoneme, the supporting structure of cilia and flagella, which perform crucial cellular functions such as signal transduction and cell motility. Given the critical role of centrioles and cilia in cell physiology, mutations in numerous centriolar proteins cause various disorders, including microcephaly, dwarfism and ciliopathies. Therefore, it is crucial to understand better the mechanisms that regulate the dynamics of centrioles and cilia. In this study, the cilia of Drosophila melanogaster type I sensory neurons have been analysed, to understand the role played by the centriolar proteins Klp10A, Cnb, Gorab and Rcd4 in the dynamics of centrioles and cilia. In Drosophila wild type sensory neurons, Klp10A (Kinesin-like protein 10A), a member of the kinesin-13 family, is located in the distal part of the transition zone (TZ), just above the UNC–GFP signal. This study shows that mutations in klp10A result in substantial structural defects of sensory neurons such as the over elongation of both centrioles in opposite directions. It has also been observed that the extensions of both centrioles, called proximal and distal basal bodies, show doublets surrounded by electron-dense material and short lateral projections as found in the control TZ. Therefore, the elongated distal regions of the centrioles in klp10A mutants may be equivalent to a TZ. The phenotype observed in klp10A mutant is deeply different from that observed in sensory neurons of mutants for other TZ proteins that are limited to the proximal portion of the TZ. This suggests that Klp10A could be a core component of the ciliary transition zone in Drosophila, specifically associated with the distal region of the TZ where it plays an essential role in centriole elongation and the assembly and maintenance of the ciliary axoneme. Centrobin (Cnb) is a centrosome-associated protein that localizes specifically at the daughter centrioles. It has been shown that a cnb mutation makes the daughter centrioles, called PBBs in this model, able to act as distal basal bodies (DBBs) to nucleate supernumerary axonemes. This is confirmed by the present study performed on a different cnb mutant strain, suggesting that Cnb acts as a negative regulator of ciliogenesis. Recently a new centriolar protein required for centriole duplication, called Gorab, has been discovered in Drosophila melanogaster. The cnb-gorab double mutant sensory neurons analysed in this study, show a stronger centriole reduction compared to the single gorab mutant. Consequently, the number of cilia is also severely affected. These findings suggest that in the cnb-gorab mutant, the centriole duplication fails before the basal body formation. Recent works have identified the human protein called PPP1R35 (Rcd4 in Drosophila - Reduction in Cnn dots 4), that is involved in centriole-to-centrosome conversion (CCC) and centriole elongation. Here we demonstrate that rcd4 mutant sensory neurons show a severe centriole and cilia reduction, accompanied by centriolar fragmentation. This suggests that Rcd4 could be involved in the CCC similarly to its human counterpart.
Per via del suo ruolo essenziale nell'omeostasi cellulare e tissutale, la struttura, la funzione e il numero di centrosomi sono altamente regolati per garantire il naturale sviluppo degli organismi, attraverso l'assemblaggio di una molteplicità di complessi proteici. Poiché l'organizzazione e l'integrità del centrosoma dipendono dai centrioli e dal materiale pericentriolare (PCM) che lo compongono, comprendere la dinamica di questi organelli è fondamentale per decifrare il comportamento del centrosoma. Ad oggi, abbiamo una conoscenza abbastanza dettagliata della composizione e della struttura dei centrioli e anche di ciò che riguarda il processo di duplicazione e maturazione centrosomale. Si conosce qualcosa del processo di eliminazione dei centrioli durante la gametogenesi, ma si sa molto poco su come i centrioli vengono eliminati nelle cellule differenziate post-mitotiche. Durante lo sviluppo dell'occhio di Drosophila, i centrioli delle cellule retiniche in differenziazione non reclutano la γ-Tubulina, suggerendo che non sono in grado di organizzare centri di organizzazione dei microtubuli (MTOC) funzionali. Coerentemente con questa ipotesi, questo studio mostra che Cnn e Spd-2, proteine che consentono il reclutamento di γ-tubulina, e DPlp, che è coinvolta nell'organizzazione del materiale pericentriolare, non vengono accumulati dai centrioli delle cellule del terzo stadio larvale. Nonostante la perdita di questi componenti essenziali del materiale pericentriolare, i centrioli sono strutturalmente intatti e possono reclutare Asl e ANA-1. Di solito, l'accumulo di Asl e ANA-1 consente ai centrioli figli di acquisire la condizione di maternità. Infatti, i centrioli madre accumulano correttamente Plk-4; tuttavia, non sono in grado di duplicare. Questi risultati mostrano che, in questo modello, l'accumulo di Plk-4 non è sufficiente per consentire la duplicazione di centrioli. Durante la progressione dello sviluppo della pupa, il numero di centrioli diminuisce progressivamente, e iniziano a essere osservati difetti strutturali. Questi fenotipi suggeriscono che l'eliminazione dei centrioli inizia con la perdita dell'integrità strutturale, piuttosto che con la riduzione del PCM, come mostrato in altri modelli. Inoltre, Asl, ANA-1 e Sas-4 sono ancora rilevabili, sottolineando che queste proteine da sole non sono in grado di garantire il mantenimento dell'integrità dei centrioli. Tra le funzioni cellulari essenziali svolte dai centrioli, vi è la loro capacità di agire come basal bodies per nucleare l'assonema, la struttura portante di ciglia e flagelli, che svolgono importanti funzioni cellulari come la trasduzione del segnale e la motilità cellulare. Dato il ruolo critico dei centrioli e delle ciglia nella fisiologia cellulare, le mutazioni di numerose proteine centriolari causano vari disturbi, tra cui microcefalia, nanismo e ciliopatie. Pertanto, è fondamentale comprendere meglio i meccanismi che regolano la dinamica dei centrioli e delle ciglia. In questo studio sono state analizzate le ciglia dei neuroni sensoriali di tipo I della Drosophila melanogaster, per comprendere il ruolo svolto dalle proteine centriolari Klp10A, Cnb, Gorab e Rcd4 nelle dinamiche di centrioli e ciglia. Nei neuroni sensoriali di tipo I di Drosophila, Klp10A (Kinesin-like protein 10A), un membro della famiglia delle kinesine 13, si localizza nella parte distale della zona di transizione (TZ), appena sopra il segnale UNC-GFP. Questo studio mostra che la mutazione di klp10A provoca sostanziali difetti strutturali dei neuroni sensoriali, come l'eccessivo allungamento di entrambi i centrioli in direzioni opposte. È stato anche osservato che le estensioni di entrambi i centrioli, chiamati basal bodies prossimale e distale, mostrano doppietti circondati da materiale elettrondenso e brevi sporgenze laterali come si quelle che si trovano nella TZ di controllo. Pertanto, le regioni distali allungate dei centrioli dei mutanti per klp10A, possono essere equivalenti a TZ. Il fenotipo osservato nel mutante klp10A è profondamente diverso da quello osservato nei neuroni sensoriali dei mutanti per altre proteine della TZ che sono limitate alla porzione prossimale. Ciò suggerisce che Klp10A potrebbe essere un componente chiave della zona di transizione ciliare in Drosophila, specificamente associato alla regione distale della TZ dove svolge un ruolo essenziale nell'allungamento dei centrioli e nell'assemblaggio e nell mantenimento dell'assoneema ciliare. La Centrobina (Cnb) è una proteina centrosomale che si localizza specificamente nei centrioli figli. È stato dimostrato che la mutazione della cnb rende i centrioli figli, chiamati PBB in questo modello, in grado di agire come basal body distali (DBB) per nucleare assonemi soprannumerari. Ciò è confermato da questo studio condotto in un diverso ceppo mutante di cnb che suggerisce che la Cnb agisce come regolatore negativo della ciliogenesi. In Drosophila melanogaster, è stata scoperta una nuova proteina centriolare essenziale per la duplicazione dei centrioli, Gorab. I neuroni sensoriali del doppio mutante cnb-gorab analizzati in questo studio, mostrano una riduzione più forte dei centrioli rispetto al singolo mutante gorab. Di conseguenza, anche il numero di ciglia è gravemente colpito. Questi risultati suggeriscono che nel mutante cnb-gorab, la duplicazione dei centrioli fallisce prima della formazione del basal body. Lavori recenti hanno identificato la proteina umana chiamata PPP1R35 (Rcd4 in Drosophila - Reduction in Cnn dots 4), che è coinvolta nella conversione centriolocentrosoma (CCC) e nell’allungamento di centriolo. Le analisi dei neuroni sensoriali mutanti di Rcd4 mostrano una forte riduzione dei centrioli e delle ciglia e anche la frammentazione centriolare. Ciò suggerisce che Rcd4 potrebbe essere coinvolto nella CCC in modo simile alla sua controparte umana.

Centrosome duplication is coupled with cell division to ensure that centrosome is duplicated only once per cell cycle. This coupling, however, can be altered in specific developmental contexts although how this uncoupling occurs remains generally unclear. In C. elegans, the larval intestinal and the hypodermal cells will endocycles, while germ line stem cells eventually exit mitosis and enter meiosis. We use these models to better understand how the centrosome is intimately coupled to the cell cycle and the mechanisms though which the duplication of the centrioles can be uncoupled from cell division during the course of development.By monitoring the levels of SPD-2, a protein that is critical for centriole duplication in C. elegans, we found that the centriole duplicates normally at the intestinal cell nuclear division, but does not re-duplicate during the first endocycle, Subsequently SPD-2 becomes diffuse within the nucleus before it is subsequently eliminated. These dynamic changes seem to be actively regulated since they are not observed in situations of un-quantized DNA re-replication. To test whether cell cycle regulators might regulate centrosome/cell cycle uncoupling and elimination, we generated phosphomimetic and non-phosphorylable variants of SPD-2. We found that altering the highly conserved CDK-phosphorylation site of Serine 545 uncouples the centriole duplication/cell cycle coupling, whereas mimicking PLK-mediated phosphorylation or reducing the activity of ubiquitylation pathway by RNAi leads to nuclear accumulation of SPD-2 potentially by stabilizing SPD-2 without affecting centrosome duplication and uncoupling. Overall our study reveals that phosphorylation of SPD-2 by key cell cycle kinases may regulate centrosome/cell cycle uncoupling and elimination during in C.elegans development.Secondly, we studied the role of RNF-1, a RING-domain protein that interacts with Cip/Kip family member CKI-2 in C. elegans. We found that RNF-1 mediates the ubiquitylation of CKI-2, which consequently results in its proteasome-dependent degradation. Consistent with this, RNF-1 reduces the embryonic lethality caused by misexpression of CKI-2. We also found that RNF-1 is localized at nuclear periphery, although the significance of this localization still requires further characterization.Finally, we analyzed the localization and the function of γ-tubulin during germ cell progression. We found that γ-tubulin undergoes a re-distribution from its association with the centriole to germ cell membrane at the onset of meiosis. This re-distribution causes the centriole to lose its microtubule nucleating capacity and appears to be triggered by signals that occur during the mitosis-meiosis transition. We are continuing a characterization of the significance and the mechanism of this re-distribution.
La duplication des centrosomes est couplé à la division cellulaire afin qu'elle n'ait lieu qu'une seule fois par cycle cellulaire. Cependant, lors de certains contextes développementaux, ce couplage n'a pas lieu et ceci reste mal compris à ce jour. Chez C. elegans, alors que les cellules hypodermales et intestinales font de l'endo-replication, les cellules souches germinales sortent de la mitose pour entrer en méiose. L'utilisation de ces différents modèles cellulaires, nous permet de mieux comprendre comment la duplication des centrosomes est dans la plupart des cas intimement couplée au cycle cellulaire, et d'étudier les mécanismes où la duplication des centrioles est indépendante à la division cellulaire au cours de contextes développementaux particuliers.SPD-2 est une protéine essentielle à la duplication des centrioles chez C.elegans. En observant ses niveaux d'expression, nous avons pu montré qu'alors que les centrioles sont correctement dupliqués lors de la division des cellules intestinales, ils ne se re-dupliquent pas au cours du 1er-cycle d'endo-replication. En effet, SPD-2 diffuse dans le noyau, avant d'être éliminé. Cette dynamique semble être activement régulée, car elle n'est pas observée dans des situations où l'ADN est très anormalement répliqué. Afin d'étudier l'importance des régulateurs du cycle cellulaire dans ce découplage centrosome/cycle cellulaire, nous avons généré des variants SPD-2, phosphomimétiques ou non-phosphorylables. De manière très intéressante, la modification de la serine 545, site très conservé pour la phosphorylation par CDK, entraine le découplage de la duplication du centriole par rapport au cycle cellulaire. Au contraire, en mimant la phosphorylation par PLK ou en diminuant l'activité de la voie de l'ubiquitylation, par ARNi, la protéine SPD-2 s'accumule dans le noyau. Cette accumulation est probablement due à la stabilisation de la protéine, mais elle n'affecte pas la duplication du centrosome. Notre étude révèle donc l'importance des phosphorylations de SPD-2 par différentes kinases clés du cycle cellulaire dans la régulation son activité. En effet, celles ci pourraient réguler le découplage de la duplication des centrosomes du cycle cellulaire et affecter leur élimination au cours du développement chez C. elegans.Parallèlement, nous nous sommes aussi intéressé au rôle de RNF-1, une protéine contenant des domaines RING qui interagit avec CKI-2, un membre de la famille Cip/Kip. Nous avons démontré que RNF-1 joue un rôle crucial dans l'ubiquitylation de CKI-2, qui est alors dégradé par la voie du protéasome. Ainsi, l'expression de RNF-1 réduit la létalité embryonnaire causée lors d'une mauvais expression de CKI-2. RNF-1 se localise à la périphérie du noyau, toutefois la fonction associée à cette localisation nécessite une étude plus approfondie.Finalement, nous avons etudié le rôle de la γ-tubuline au cours de la progression des cellules germinales. Nous avons trouvé que la γ-tubuline est redistribuée depuis sa localisation centriolaire vers la membrane cytoplasmique des cellules germinales pendant la méiose. Cette redistribution inhibe les capacités du centriole à générer la nucléation des microtubules, ceci résultant probablement de signaux transmis lors de la transition entre la mitose et la méiose. Nous continuons notre travail afin de comprendre le rôle et les mécanismes impliqués dans cette redistribution.