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.

The emb-1 and emb-3 Gene Functions are Required for the Meiosis After Fertilization

Kiyoji Nishiwaki and Johji Miwa

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.