Worm Breeder's Gazette 10(2): 55
These abstracts should not be cited in bibliographies. Material contained herein should be treated as personal communication and should be cited as such only with the consent of the author.
In C. elegans, oocytes at the diakinesis stage, which is a final stage of the meiosis-I prophase, quickly enter the metaphase after fertilization. Two polar bodies are successively formed during the meiosis after fertilization and the pronuclei are reconstructed after the completion of meiosis-II. Miwa et al.(1980) and Schierenberg et al.(1980) identified 9 genes required for C. elegans embryogenesis. The gene function of two of these, emb-1 and emb-3, is necessary very early in the embryogenesis. Reconstruction of the pronuclei is defective in emb-1(hc57). Early divisions are variably abnormal in emb-3(hc59). We have studied the possibility that these early abnormalities are caused by defective meiotic events in the mutants. We stained the meiotic spindle and the chromosomes of the fertilized egg with an anti-tubulin antibody and DAPI. The meiotic spindle of N2 was spherical or barrel-like in both meiosis-I and -II, as was observed by Albertson(1984). The 6 bivalent chromosomes were arranged pentagonally with one of them in the center. In the emb-1(hc57) mutant, although the meiosis-I spindle was formed and the homologous chromosomes were separated from each other, no polar body was produced. Both oocyte and sperm chromosomes gradually degraded after the homologs separated and no cell division followed . As for the emb-3( hc59) mutant, about 40% of the embryos examined exhibited the disordered meiosis-I spindle structure and the abnormal arrangement of the paired homologs. Although the homologs were separated, they were all extruded together as a single large polar body. The male pronucleus was, however, reconstructed and the development, which did not appear to be completely abnormal, continued in the haploid state. We observed haploid embryos with several hundred cells. These results indicate that both emb-1 and emb-3 gene functions are required for the meiosis after fertilization, but that each gene plays an apparently different role. The construction of the meiosis-I spindle seems to need the emb-3 gene function, but not the emb-1 gene function. Also, the polar body formation appears to require both the emb-1 gene and possibly the emb-3 gene to function. The emb-3 gene probably acts before the emb-1 gene in meiosis-I. Schierenberg et al. (1985) observed strong cytoplasmic streaming in the wild-type embryos of the mechanically denucleated female pronucleus, which arrested before hatching. We observed the similar abnormality with the emb-3 embryos without the female pronucleus.