A tool to promote experimental zoology at the end of the 19th century: the creation of the “Archives de Zoologie Expérimentale et Générale”

1872, France. An eminent zoologist of the time, Henri de Lacaze-Duthiers, realises one of his most important goals: he creates a new journal, focused on zoological discoveries, which he calls “Archives de Zoologie Expérimentale et Générale”. His motivations were threefold. the first was to participate in the intellectual reconstruction of France, humiliated by the defeat against Prussia in 1871. the second was to promote a new way of conceiving and doing zoology: zoology should be approached through experience (and not just observation), and it should be general, including everything related to animal life (embryology, physiology, histology, ecology). the third was to acquire freedom and autonomy by liberating himself from the conservative journal that had a quasi-monopoly on zoology at the time, “les Annales de sciences naturelles”. the Archives, which had a difficult start, had an impressive success, revealing young talents from all over Europe and reporting on major discoveries, until their last issue in 1981. this article recounts their adventure.journal articl

ARPP19 Phosphorylations by PKA and Greatwall: The Yin and the Yang of the Cell Decision to Divide

Entry into mitosis and meiosis is orchestrated by the phosphorylation of thousands of mitotic substrates under the control of active Cdk1-cyclin B complexes. To avoid futile cycles of phosphorylation/dephosphorylation, the specific Cdk1-antagonizing phosphatase, PP2A-B55δ, must be simultaneously inactivated. This process is achieved by the activation of the kinase Greatwall (Gwl), which phosphorylates ARPP19. Gwl-phosphorylated ARPP19 then inactivates PP2A-B55δ to allow Cdk1 activation as well as to secure the phosphorylation state of mitotic substrates. This chapter discusses a series of recent works showing that ARPP19 is also phosphorylated by another kinase, PKA. Phosphorylated by PKA, ARPP19 arrests Xenopus oocytes in G2 before the first meiotic division. Therefore, depending on its phosphorylation state by either PKA or Gwl, ARPP19 either restrains or activates Cdk1 in Xenopus oocytes. Beyond the understanding of the mechanisms of meiotic and mitotic cell division, the control of ARPP19 by its dual phosphorylation enlightens the cAMP-regulated signalization pathways that control vital functions in numerous eukaryotic cell types

Mos in the Oocyte: How to Use MAPK Independently of Growth Factors and Transcription to Control Meiotic Divisions

In many cell types, the mitogen-activated protein kinase (MAPK) also named extracellular signal-regulated kinase (ERK) is activated in response to a variety of extracellular growth factor-receptor interactions and leads to the transcriptional activation of immediate early genes, hereby influencing a number of tissue-specific biological activities, as cell proliferation, survival and differentiation. In one specific cell type however, the female germ cell, MAPK does not follow this canonical scheme. In oocytes, MAPK is activated independently of growth factors and tyrosine kinase receptors, acts independently of transcriptional regulation, plays a crucial role in controlling meiotic divisions, and is under the control of a peculiar upstream regulator, the kinase Mos. Mos was originally identified as the transforming gene of Moloney murine sarcoma virus and its cellular homologue was the first proto-oncogene to be molecularly cloned. What could be the specific roles of Mos that render it necessary for meiosis? Which unique functions could explain the evolutionary cost to have selected one gene to only serve for few hours in one very specific cell type? This review discusses the original features of MAPK activation by Mos and the roles of this module in oocytes

Unfertilized Xenopus Eggs Die by Bad-Dependent Apoptosis under the Control of Cdk1 and JNK

Ovulated eggs possess maternal apoptotic execution machinery that is inhibited for a limited time. The fertilized eggs switch off this time bomb whereas aged unfertilized eggs and parthenogenetically activated eggs fail to stop the timer and die. To investigate the nature of the molecular clock that triggers the egg decision of committing suicide, we introduce here Xenopus eggs as an in vivo system for studying the death of unfertilized eggs. We report that after ovulation, a number of eggs remains in the female body where they die by apoptosis. Similarly, ovulated unfertilized eggs recovered in the external medium die within 72 h. We showed that the death process depends on both cytochrome c release and caspase activation. The apoptotic machinery is turned on during meiotic maturation, before fertilization. The death pathway is independent of ERK but relies on activating Bad phosphorylation through the control of both kinases Cdk1 and JNK. In conclusion, the default fate of an unfertilized Xenopus egg is to die by a mitochondrial dependent apoptosis activated during meiotic maturation

11. Environnement et développement animal

Le développement animal couvre la période du devenir de l’œuf en un organisme juvénile* autonome. Selon les modalités du développement, l’embryon et la larve, quand elle existe, sont confrontés plus ou moins directement à l’environnement extérieur. Les embryons et fœtus des mammifères bénéficient d’un milieu de vie protégé et stable, leur développement ayant lieu au sein de l’organisme maternel. Mais chez la majorité des espèces, qualifiées d’« ovipares* », l’œuf est pondu dans le milieu exte..

Etude de la régulation de la protéine kinase Aurora-A au cours de la maturation méiotique de l'ovocyte de xénope

LE KREMLIN-B.- PARIS 11-BU Méd (940432101) / SudocPARIS-BIUP (751062107) / SudocSudocFranceF

De la progestérone à l'activation du MPF dans l'ovocyte de Xénope (quels rôles pour H-Ras et la kinase Myt1 ?)

L objectif était d améliorer la compréhension des mécanismes présidant à l activation du MPF (M-Phase promoting Factor). Le modèle d étude a été les divisions méiotiques de l ovocyte de Xénope. Ils sont naturellement bloqués en prophase de méiose I. En réponse à la progestérone, ils reprennent la méiose et se re-bloquent en métaphase II en attente de la fécondation. Ce processus, appelé maturation méiotique, est sous le contrôle du complexe Cdc2-Cycline B, facteur universel de division des cellules eucaryotes. Nous avons étudié la régulation de Myt1, une kinase qui catalyse les phosphorylations inhibitrice sur la protéine Cdc2 et est donc responsable du maintien du MPF sous une forme inactive pendant la phase G2. L activation du MPF repose sur la conversion du stock de pré-MPF inactif en stock de MPF actif, suite à la déphosphorylation activatrice de Cdc2 par la phosphatase Cdc25, et à l inhibition de Myt1. Nous avons montré que l activité de Cdc2 était nécessaire à l inhibition de Myt1 et que deux kinases, p90Rsk et Plx1, sont recrutées l une ou l autre pour contribuer à cette inhibition. Puis, nous avons étudié l implication de la protéine H-Ras lors de la reprise de la méiose. Nous avons montré que l injection de H-Ras induit la reprise de la méiose par le recrutement d une PI3 kinase particulière. Cette voie, bien que présente et activable dans l ovocyte, n est pas recrutée in vivo par la progestérone en conditions normales. L ovocyte est donc équipé de plusieurs voies de signalisation fonctionnellement redondantes, qui peuvent être recrutées dans des conditions pathologiques pour assurer la reprise de la méiose quand les effecteurs normaux ne sont pas disponibles.PARIS-BIUSJ-Thèses (751052125) / SudocPARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF

Function and regulation of cdc25 protein phosphatase through mitosis and meiosis

116 ref. chap. 17International audienc

<em>Xenopus</em> cyclin D2: cloning and expression in oocytes and during early development

International audienceWe have isolated and characterized a cDNA which contains the entire coding sequence of Xenopus laevis cyclin D2 protein. Cyclin D2 mRNA is identified as a member of the class of maternal RNAs. It is rare and stable during embryonic development at least until tadepole. In addition, a second cDNA coding for a truncated version of cyclin D2 was also isolated. Microinjection of cyclin D2 into oocytes undergoing meiotic maturation and parthenogenetic activation reveals that the protein is stable for several hours, independently of the ubiquitin-mediated degradation of cyclin B2 that takes place periodically during this process. Microinjected cyclin D2 localizes both in the cytoplasm and in the nucleus of oocyte. In somatic cells, it is well established that cyclin D2 is almost exclusively nuclear and very labile. The unusual behaviour of cyclin D2 upon injection into oocytes may provide indications about a possible role for this protein during meiosis and early development