Abstracts
Résumé
L’embryon du nématode Caenorhabditis elegans représente un système expérimental de choix pour disséquer les mécanismes qui orchestrent les processus de division cellulaire dans un organisme multicellulaire. En effet, un faisceau d’approches cellulaires, génétiques, moléculaires et génomiques permettent d’aborder chez cet organisme nombre de questions fondamentales relatives à la division cellulaire. Certaines des molécules caractérisées chez ce nématode pourraient jouer un rôle important dans d’autres organismes, y compris l’être humain. Dès lors, la recherche fondamentale menée sur l’embryon de C. elegans devrait avoir, à terme, un impact significatif sur le développement de nouveaux outils diagnostiques et thérapeutiques.
Summary
The mechanisms orchestrating spatial cell division control remain poorly understood. In animal cells, the position of the mitotic spindle dictates cleavage furrow placement, and thus plays a key role in governing spatial relationships between resulting daughter cells. The one-cell stage Caenorhabditis elegans embryo is an attractive model system to investigate the mechanisms underlying spindle positioning in metazoans. In this review, the experimental advantages of this model system for an in vivo dissection of cell division processes are first discussed. Next, three lines of experiments that were conducted to dissect the mechanisms governing spindle positioning in one-cell stage C. elegans embryos are summarized. First, localized laser micro-irradiations were utilized to identify the forces acting on spindle poles during anaphase. This work revealed that there is a precise imbalance of pulling forces acting on the two spindle poles, with the forces acting on the posterior spindle pole being in slight excess, thus explaining the asymmetric spindle position achieved by the end of anaphase. Second, an RNAi-based fonctional genomic screen was carried out to identify novel components required for generating these pulling forces. This uncovered that gpr-1/gpr-2, which encode GoLoco-containing proteins, as well as the previously identified Ga subunits goa-1/gpa-16, are required for generation of pulling forces on the spindle poles. Third, the zyg-8 locus was identified by mutational analysis to play a distinct role during anaphase spindle positioning. zyg-8 was found to encode a protein related to human Doublecortin, which is affected in patients with neuronal migration disorders. Moreover, ZYG-8 is a microtubule-associated protein that stabilizes microtubules against depolymerization. Together, these experimental approaches contribute to a better understanding of the mechanisms orchestrating spatial cell division control in metazoan organisms.
Appendices
Références
- 1. Sausville EA. Complexities in the development of cyclin-dependent kinase inhibitor drugs. Trends Mol Med 2002; 8: S32-7.
- 2. Rappaport R. Cytokinesis in animal cells. Int Rev Cytol 1971; 31: 169-213.
- 3. Wallenfang MR, Seydoux G. Polarization of the anterior-posterior axis of C. elegans is a microtubule-directed process. Nature 2000; 408 : 89-92.
- 4. Goldstein B, Hird SN. Specification of the anteroposterior axis in Caenorhabditis elegans. Development 1996; 122: 1467-74.
- 5. Kemphues KJ, Strome S. Fertilization and establishment of polarity in the embryo. In: Riddle DL, Blumenthal T, Meyer BJ, Priess JR, eds. C. elegans II. New York : Cold Spring Harbor Laboratory Press, 1997 : 335-59.
- 6. Gotta M, Ahringer J. Axis determination in C. elegans: initiating and transducing polarity. Curr Opin Genet Dev 2001; 11 : 367-73.
- 7. Etemad-Moghadam B, Guo S, Kemphues KJ, Asymmetrically distributed PAR-3 protein contributes to cell polarity and spindle alignement in early C. elegans embryos. Cell 1995; 83: 743-52.
- 8. Hung TJ, Kemphues KJ. PAR-6 is a conserved PDZ domain-containing protein that colocalizes with PAR-3 in Caenorhabditis elegans embryos. Development 1999; 126: 127-35.
- 9. Boyd L, Guo S, Levitan D, Stinchcomb DT, Kemphues KJ. PAR-2 is asymmetrically distributed and promotes association of P granules and PAR-1 with the cortex in C. elegans embryos. Development 1996; 122: 3075-84.
- 10. Guo S, Kemphues KJ. par-1, a gene required for establishing polarity in C. elegans embryos, encodes a putative Ser/Thr kinase that is asymmetrically distributed. Cell 1195; 81: 611-20.
- 11. Izumi Y, Hirose T, Tamai Y, et al. An atypical PKC directly associates and colocalizes at the epithelial tight junction with ASIP, a mammalian homologue of Caenorhabditis elegans polarity protein PAR-3. J Cell Biol 1998; 143: 95-106.
- 12. Bohm H, Brinkmann V, Drab M, Henske A, Kurzchalier TV. Mammalian homologues of C. elegans PAR-1 are asymmetrically localized in epithelial cells and may influence their polarity. Curr Biol 1997; 7: 603-6.
- 13. Kemphues K. PARsing embryonic polarity. Cell 2000; 101: 345-8.
- 14. Mello CC, Schubert C, Draper B, et al. The PIE-1 protein and germline specification in C. elegans embryos. Nature 1996; 382: 710-2.
- 15. Schubert CM, Lin R, de Vries CJ, Plasterk RH, Priess JR. MEX-5 and MEX-6 function to establish soma/germline asymmetry in early C. elegans embryos. Mol Cell 2000; 5: 671-82.
- 16. Bowerman B. Maternal control of pattern formation in early Caenorhabditis elegans embryos. Curr Top Dev Biol 1998; 39: 73-117.
- 17. Sulston JE, Schierenberg E, White JG, Thomson JN. The embryonic cell lineage of the nematode Caenorhabditis elegans. Dev Biol 1983; 100: 64-119.
- 18. Oegema K, Desai A, Rybina M, Kirkham M, Hyman AA. Functional analysis of kinetochore assembly in Caenorhabditis elegans. J Cell Biol 2001; 153: 1209-26.
- 19. Strome S, Wood WB. Generation of asymmetry and segregation of germ-line granules in early C. elegans embryos. Cell 1983; 35: 15-25.
- 20. Hyman AA. Centrosome movement in the early divisions of Caenorhabditis elegans: a cortical site determining centrosome position. J Cell Biol 1989; 109: 1185-93.
- 21. Gönczy P, Schnabel H, Kaletta T, et al. Dissection of cell division processes in the one cell stage Caenorhabditis elegans embryo by mutational analysis. J Cell Biol 1999; 144: 927-46.
- 22. O’Connell KF, Leys CM, White JG. A genetic screen for temperature-sensitive cell-division mutants of Caenorhabditis elegans. Genetics 1998; 149: 1303-21.
- 23. Fraser AG, Kamath RS, Zipperlen P, Martinez-Campos M, Sohmann M, Ahringer J. Functional genomic analysis of C. elegans chromosome I by systematic RNA interference. Nature 2000; 408: 325-30.
- 24. Gönczy P, Echeverri G, Degema K, et al. Functional genomic analysis of cell division in C. elegans using RNAi of genes on chromosome III. Nature 2000 ; 408: 331-6.
- 25. Piano F, Schetter AJ, Mangona M, Stain L, Komphues KJ. RNAi analysis of genes expressed in the ovary of Caenorhabditis elegans. Curr Biol 2000; 10: 1619-22.
- 26. Maeda I, Kohara Y, Yamamoto M, Sugimoto A. Large-scale analysis of gene function in Caenorhabditis elegans by high-throughput RNAi. Curr Biol 2001; 11: 171-6.
- 27. Kemphues KJ, Priess JR, Morton DG, Cheng NS. Identification of genes required for cytoplasmic localization in early C. elegans embryos. Cell 1988; 52: 311-20.
- 28. Grill SW, Gönczy P, Stelzer EH, Hymen AA. Polarity controls forces governing asymmetric spindle positioning in the Caenorhabditis elegans embryo. Nature 2001; 409: 630-3.
- 29. Leslie RJ, Pickett HJ. Ultraviolet microbeam irradiations of mitotic diatoms: investigation of spindle elongation. J Cell Biol 1983; 96: 548-61.
- 30. Aist JR, Liang H, Mangona M, Stain L, Komphues KJ. Astral and spindle forces in PtK2 cells during anaphase B: a laser microbeam study. J Cell Sci 1993; 104: 1207-16.
- 31. Gotta M, Ahringer J. Distinct roles for Gα and Gβγ in regulating spindle position and orientation in Caenorhabditis elegans embryos. Nat Cell Biol 2001; 3: 297-300.
- 32. Schaefer M, Petronczki M, Dorner D, Forto M, Knoblirh JA. Heterotrimeric G proteins direct two modes of asymmetric cell division in the Drosophila nervous system. Cell 2001; 107: 183-94.
- 33. Schaefer M, Shevchenko A, Knoblich JA. A protein complex Shevchemke A, containing Inscuteable and the Gα-binding protein Pins orients asymmetric cell divisions in Drosophila. Curr Biol 2000; 10: 353-62.
- 34. Roychowdhury S, Panda D, Wilson L, Rasemick MH. G protein α subunits activate tubulin GTPase and modulate microtubule polymerization dynamics. J Biol Chem 1999; 274: 13485-90.
- 35. Gönczy P, Bellanger JM, Kirkham M, et al. zyg-8, a gene required for spindle positioning in C. elegans, encodes a doublecortin-related kinase that promotes microtubule assembly. Dev Cell 2001; 1: 363-75.
- 36. des Portes V, Pinard JM, Billuart P, et al. A novel CNS gene required for neuronal migration and involved in X-linked subcortical laminar heterotopia and lissencephaly syndrome. Cell 1998; 92: 51-61.
- 37. Gleeson JG, Allen KM, Fox JW, et al. Doublecortin, a brain-specific gene mutated in human X-linked lissencephaly and double cortex syndrome, encodes a putative signaling protein. Cell 1998; 92: 63-72.
- 38. O’Connell KF, Caron C, Kopish KR, et al. The C. elegans zyg-1 gene encodes a regulator of centrosome duplication with distinct maternal and paternal roles in the embryo. Cell 2001; 105: 547-58.
- 39. Jantsch-Plunger V, Gönczy P Romano A, et al. CYK-4, a rho family GTPase activating protein (gap) required for central spindle formation and cytokinesis. J Cell Biol 2000; 149: 1391-404.
- 40. Mishima M, Kaitna S, Glotzer M, et al. Central spindle assembly and cytokinesis require a kinesin-like protein/RhoGAP complex with microtubule bundling activity. Dev Cell 2002; 2:41-54.
- 41. Fire A, Xu S, Montgomery MK, Kostas SA, Driver SE, Mello CC. Potent and specific genetic interference by double-stranded RNA in Caenorhabditis elegans. Nature 1998; 391: 806-11.
- 42. Zipperlen P, Fraser AG, Lendeckel W, Yalcin A, Welber K, Tuschl T. Roles for 147 embryonic lethal genes on C. elegans chromosome I identified by RNA interference and video microscopy. EMBO J 2001; 20: 3984-92.
- 43. Elbashir SM, Harborth J, Duplexes of 21-nucleotide RNAs mediate RNA interference in cultured mammalian cells. Nature 2001; 411: 494-8.
- 44. Gönczy P. Mechanisms of spindle positioning in flies and worms. Trends Cell Biol 2002; 12: 332-9.