Worm Breeder's Gazette 12(3): 82 (June 15, 1992)

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.

A Novel Member of the POU-Gene Family in C. elegans: ceh-18 is Expressed by Many Cells but Few Neurons

David Greenstein, Gary Ruvkun

Department of Genetics, Harvard Medical School, & Department of Molecular Biology, Massachusetts General Hospital, Boston, MA O2114

The POU domain is a protein motif consisting of a specialized homeodomain and an adjacent region of extended sequence similarity first found to be shared between the C. elegans cell lineage control gene unc-86 and the mammalian transcription factors Pit-l, Oct-l, and Oct-2 .The POU domain directs cooperative binding to specific DNA sequences. We are undertaking a combined molecular and genetic analysis of ceh-18 ,a member of the POU family that defines a new class of POU proteins. We hope to address the roles that ceh-18 might play in specifying cell fate or controlling cell lineage.

We have analyzed the expression pattern of ceh-18 using in situ hybridization and antibody staining. Since we do not yet have a ceh-18 protein null mutant, we cannot be sure that all the immunoreactivity is ceh-18 protein. However, we have obtained identical results using affinity-purified antisera from two rabbits and these results are consistent with the in situ hybridization analyses. Moreover, the antisera detect a 69 kdal protein in Western blots of worm extracts that comigrates with ceh-18 protein produced in E. coli. In contrast to unc-86 ,which is only expressed in neuroblasts and neurons, ceh-18 is expressed in a variety of different cell types, but is notably absent from nearly all neurons. The distribution of ceh-18 protein expression is dynamic with a variety of different cells expressing the protein depending on developmental stage. ceh-18 protein is expressed weakly in the maternal germline precursors and in immature oocytes but has not been seen in sperm. ceh-18 immunoreactivity is found in the male and female pronuclei prior to the first division but gets progressively weaker and disappears by gastrulation. By in situ hybridization, ceh-18 mRNA is first detected at the three-fold stage of embryogenesis and is most abundant in pharyngeal muscle cells, hypodermal cells of the head and tail, and body muscle cells. Consistent with this finding, the anti- Ceh-18 antisera stain the nuclei of the pharyngeal muscle cells, hypodermal cells, and body muscle cells at hatching. The staining of the pharyngeal muscle nuclei is particularly bright at hatching, but gets progressively weaker and disappears by the end of L1 .Many of the hypodermal cells of the head and tail (hyp 3-6 and hyp 8-10) also stain much more weakly after hatching. The P hypodermal blast cells express ceh-18 protein at hatching and during their ventral migration, but ceh-18 protein disappears from the P-cell nuclei when they take up their ventral positions. in the lateral hypodermal cell lineages, changes in ceh-18 expression correlate with changes in cell fates. The anterior daughters of the lateral hypodermal blast cells fuse with the large hypodermal syncytium, hyp7 .After or during cell fusion (we can't tell), the nuclei of these daughters are seen to stain strongly with the anti- Ceh-18 antiserum. This implies that these nuclei either make Ceh-18 protein themselves or obtain it from the syncytium they have joined. Both distal tip cells stain weakly from their birth up until mid-late L2 when they stain brightly. This bright staining persists through adulthood. The intestinal cell nuclei stain from hatching through adulthood, though the staining appears to be weaker after molts. Of the 302 neurons, only three, the anterior touch cells (ALML/R and AVM), express the ceh-18 protein. This is interesting to us because there is no known gene that specifically affects the anterior touch cells. We are performing antisense and ectopic expression experiments to further probe the function of ceh-18 in development.