Fate specification of the four male-specific blast cells (termed F, U, B, and Y) of the C. elegans tail is a useful system to investigate developmental patterning within a tissue. In both newly-hatched males and hermaphrodites, these four cells are part of the rectal epithelium, but each cell has a distinct fate. The fate differences are apparent in the morphology of the cells and the expression of different markers in both sexes. In addition, in males these cells divide postembryonically, with each producing a distinct set of differentiated progeny. Embryonically, these four cells share some lineal relationships, as F and U are sister cells, and U and B are left/right lineal homologues. In a genetic screen of over 25,000 mutagenized gametes, we identified twelve mutations in seven genes that disrupt the identity of a subset of these four cells. Four of these genes (
egl-38,
lin-48,
lin-49, and
lin-59) are required for the normal fates of the two more anterior cells, F and U. However, the specific functions of these genes are distinct. For example,
egl-38 is required to make the U cell different from its neighbor, Y, whereas
lin-48 is required to make the U cell different from its lineal homologue, B. The molecular identity of these two genes underscores the importance of transcriptional regulation in cell fate specification.
egl-38 encodes a Pax protein similar to mammalian Pax2, Pax5, and Pax8 (Chamberlin et al., 1997, Dev. 124, 3919-3928).
lin-48 encodes a C2H2 zinc finger protein most similar to the Drosophila ovo gene product. A
lin-48::gfp fusion transgene that can rescue
lin-48(
sa469) is expressed by F and U and localized to cell nuclei. We have begun to investigate how these four genes function together to specify F and U fates.
lin-48 mutant males produce ectopic spicule cells, and we have used this phenotype to carry out preliminary epistasis tests. We have found that
lin-48;
egl-38 double mutants still produce ectopic spicule cells, whereas
lin-59;
lin-48 double mutants do not. In addition,
lin-48;
lin-49 double mutants are not viable, indicating a potential genetic redundancy between these two genes. We will test
lin-48::gfp expression in the mutant backgrounds to further explore the relationship among these genes.