Worm Breeder's Gazette 14(2): 76 (February 1, 1996)
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.
ABL-Basic Research Program, FCRDC, Frederick, MD 21702
Early in embryonic development, the 5 somatic founder cells, AB, MS, E, C, and D, each have a distinct cell cycle periodicity. The cell cycle within a particular founder cell lineage is relatively synchronous within that lineage, but asynchronous with the other founder cell lineages. The two germline cells, Z2 and Z3, are born early in embryonic development, but do not divide during the remainder of embryogenesis; they do proliferate extensively during larval and adult development to generate over 1000 germline cells. We have initiated a project to examine the regulation of these cell cycles during C. elegans development. Our goals are to explore how developmental signals regulate these various cell cycles as well as to determine whether perturbation of the cell cycle can affect development. Biochemical and genetic experiments from other systems have revealed that serine/threonine kinases regulate the progression from one stage of the cell cycle to the next (i.e, CDC2, CDKs). These kinases in turn are regulated by phosphorylation and dephosphorylation. In these other systems, the regulated activity of CDC2 is required for G2 to M-phase progression. CDC2 is phosphorylated on a single tyrosine residue by WEE1 to maintain it as an inactive kinase during much of the cell cycle. This phosphotyrosine residue and an adjacent phosphothreonine residue are dephosphorylated by a dual-specificity phosphatase CDC25 to activate CDC2 for mitosis. We have begun to examine the expression of these universally conserved cell cycle regulators, namely, the tyrosine kinase, WEE1, and the dual-specificity phosphatase, CDC25, during C. elegans development. The cloning and sequence of the C. elegans cdc2 gene, ncc-1, has been described previously (Mori et al., Mol. Gen. Genet., 1994). Seydoux and Fire (Development, 1994) have shown that ncc-1 is a maternal message that perdures ubiquitously throughout embryonic development. A search of the available sequences from the Genome Consortium revealed two candidate cdc25 genes (cosmids ZK637 and R05H5; Sulston et al., Nature, 1992). The two cdc25 candidates have all of the distinguishing features that identify them as CDC25 family dual-specificity phosphatases. Using SL1, SL2, and 3¹ UTR specific primers and RT-PCR, we identified a SL1-trans-spliced cDNA for the cdc25 (ZK637) gene. We used this cdc25 cDNA for RNA in situ studies to examine the mRNA expression pattern in embryos. The ZK637 cdc25 message is maternal: it is abundant in the 1-cell embryo and is partitioned to the anterior half of the embryo. The message clearly partitions to AB in the 2-cell embryo and then to the AB progeny in the next 2-3 AB divisions. The mRNA essentially is not detectable after the 16-24 cell stage. The message is absent or at very low levels in P1 and cells derived from P1. We have not observed any embryonic transcription of this message by this in situ method. We are currently cloning the R05H5 cdc25 cDNA for RNA expression analysis. We are also testing CDC25 antibodies to determine the protein expression patterns of these cell cycle regulators throughout embryogenesis and germline development. This research was sponsored by the National Cancer Institute, DHHS, under contract with ABL.