Dynamique Cellulaire - Développement - Association de Biologie ...

9
10
11
Cycle progression depends upon signaling from ATM and Chk2 to DOA
kinase in Drosophila
Muwang LI ; muwang.li@u-psud.fr
Muwang Li, Catherine Dreux and Leonard Rabinow
Signalisation, Développement et Cancer, Bât. 442 bis, Univ. Paris Sud 11, 91400 Orsay
ATM and Chk2 kinases are best known for their function in the DNA damage-control checkpoint, blocking
cell cycle progression either at G1/S or G2/M when activated. Evidence from multiple sources has recently
suggested a critical role for the regulation of alternative splicing in cell cycle progression in Drosophila,
through effects on the splicing of transcripts encoding cell-cycle regulatory proteins such as E2F. Mutations
in the Doa locus of Drosophila, encoding a kinase regulating alternative splicing through the phosphorylation
of SR proteins, block the normal alternative splicing of these same cell-cycle regulatory transcripts. RNAi
against Doa also induces cell-cycle arrest. Moreover, Doa phenotypes, such as sex-transformation, ectopic
wing-venation and aberrant ommatidial organization are dramatically enhanced by mutations in ATM, ATR,
Chk2 and Chk1. Because yeast two-hybrid analysis has revealed protein-protein interactions between DOA
and Drosophila Chk2, we hypothesize that a novel signaling pathway exists, linking the ATM/ATR and
Chk1/2 kinases to DOA, to effect cell-cycle control.
The ESCRT-III protein CeVPS-32 is enriched in domains distinct from
CeVPS-27 and CeVPS-23
Xavier MICHELET ; michelet@cgm.cnrs-gif.fr
Xavier Michelet, Adriana Alberti, Laura Benkemoun, Nathalie Roudier, Christophe Lefebvre and Renaud
Legouis
Centre de Génétique Moléculaire, CNRS, Gif-sur-Yvette
Within the endocytic pathway, the Endosomal Sorting Complex Required for Transport (ESCRT) machinery
is essential for the biogenesis of MultiVesicular Bodies (MVB). In yeast, ESCRTs are recruited at the
endosomal membrane and involved in cargo sorting into intralumenal vesicles of the MVB. Here, we
characterize the ESCRT-III protein CeVPS-32 in the nematode C. elegans and its interactions with CeVPS-
27, CeVPS-23 and CeVPS-4. In contrast to other CevpsE genes, depletion of Cevps-32 is embryonic lethal
with severe defects in the remodelling of epithelial cell shape during organogenesis. Furthermore, Cevps-32
animals display an accumulation of enlarged early endosomes in epithelial cells and an accumulation of
autophagosomes. CeVPS-32 protein is enriched in epithelial tissues and in residual bodies during spermatid
maturation. We show that CeVPS- 32 and CeVPS-27/Hrs are enriched in distinct sub-domains at the
endosomal membrane. CeVPS-27 positive sub-domains are also enriched for the ESCRT-I protein CeVPS-
23/TSG101. The formation of CeVPS-27 sub-domains is not affected by the depletion of CeVPS-23, CeVPS-
32 or the ATPase CeVPS-4. Our data suggest that the formation of membrane sub-domains is essential for
the maturation of endosomes
Towards the reconstruction of multiscale dynamics in animal
morphogenesis
Nadine PEYRIÉRAS, Louise DULOQUIN ; nadine.peyrieras@inaf.cnrs-gif.fr
Embryomics EC project consortium http://www.embryomics.eu
Coordinator Nadine Peyrieras CNRS-DEPSN Avenue de la Terrasse 91198 Gif sur Yvette
We define the “embryome” of an organism as the multi-scale dynamics description of developmental stages
that correlates genotype and phenotype, integrating both upward and downward causation. The
reconstruction of the “embryome” first requires a paradigm of systematic investigation of the cellular
behaviours and reconstruction of the cell lineage tree as a branching process in space and time. The 4D
lineage tree is the framework to further integrate lower level dynamics (molecular and genetic) and higher
level features (cell collective behaviours and system biomechanics). The main point in discussing these
concepts is that so far biology largely escaped biological complexity. The mere accumulation of data from
high throughput strategies does not bring us any closer of powerful predictive models and processes
understanding. Gene network architecture and fate map annotation with gene expression data are not
sufficient to achieve the reconstruction of processes dynamics. The latter requires gathering quantitative
data from in vivo observation at the appropriate spatial and temporal scale for modelling gene network
dynamics and integrate dynamical processes reconstructed at the molecular and cellular level of
organisation. At the cellular level, we achieved the reconstruction of the dynamics of cell divisions,
movements and deformation from time-lapse series of high-resolution optical sections (MLSM and DSLM)
throughout development of labelled deuterostomian embryos (sea-urchin Paracentrotus lividus, ascidian
Phallusia mammillata, teleost Danio rerio) RNA injection and/or transgenesis). Original methods for low level
image treatment based on PDEs were designed to achieve 4D image filtering, nuclear centre detection,
Association de Biologie Cellulaire du Grand campus http://biocell.cnrs-gif.fr
16