[
Worm Breeder's Gazette,
1991]
Cyclin proteins are intimately involved in cell cycle regulation. Two types of cyclin proteins have been identified, cyclin A and cyclin B. The cyclin A protein has been shown to be critical to embryonic development in Drosophila; homozygous mutant embryos lacking cyclin A die when zygotic transcription fails to provide cyclin A. The presence of cyclin B protein cannot rescue these mutants (C.F. Lehner and P.H. O'Farrell, Cell 1990. 61:535-547). No mutants in cyclin B have been reported in Drosophila. Cyclin B protein has been shown to be involved in meiotic maturation in clams (Westendorf et al., J. Cell Biol. 1989. 108:1431-1444). Perhaps surprisingly, in Drosophila the mRNA for cyclin B localizes by in situ hybridization to the Drosophila pole cells, the fly equivalents of the nematode P germline cell lineage (Whitfield et al., Nature 1989. 338:337340). The Bennett laboratory is interested in the nematode germline lineage and in identifying the components of the germline P granules ( Strome and Wood, Cell 1983. 35:15-25 and K. Bennett, WBG 9:1 55). We plan to determine if nematode cyclin B RNA is similarly localized to the nematode germline precursor cells, and would like to address what possible role the sequestration of cyclin B RNA plays in the determination of the germline. Using primers to conserved cyclin B regions, we have isolated, cloned and sequenced a PCR product from genomic Caenorhabditis DNA which is a putative cyclin B. As illustrated below, this fragment has 72% exact match at the amino acid level to the corresponding region of the clam or sea urchin cyclin B genes; this is exactly the same match ( 41/57 aa) that sea urchin and clam show to each other in this region. Southern blot analysis using this fragment as a probe with C. elegans DNA indicates a single copy gene. The PCR fragment recognizes a single 1.4 kb message on Northern analysis using polyA+ RNA from mixed stage worms; this size is large enough to accommodate the coding region of the cyclin B protein. We have recently screened R. Barstead's lambda ZAP mixed stage cDNA library. Thirty putative cyclin B cDNAs were detected on duplicate lifts when 120,000 phage were screened. [See Figure 1]