MULTIPLE HOM-C GENE INTERACTIONS SPECIFY CELL FATES IN THE NEMATODE CENTRAL-NERVOUS-SYSTEM

Intricate patterns of overlapping HOM-C gene expression along the A/P axis have been observed in many organisms; however, the significance o f these patterns in establishing the ultimate fates of individual cell s is not well understood. We have examined the expression of the Caeno rhabditis elegans Antennapedia homolog mab-5 and its role in specifyin g cell fates in the posterior of the ventral nerve cord. We find that the pattern of fates specified by mab-5 not only depends on mab-5 expr ession but also on post-translational interactions with the neighborin g HOM-C gene lin-39 and a second, inferred gene activity. Where mab-5 expression overlaps with lin-39 activity, they can interact in two dif ferent ways depending on the cell type: They can either effectively ne utralize one another where they are both expressed or lin-39 can predo minate over mab-5. As observed for Antennapedia in Drosophila, express ion of mab-5 itself is repressed by the next most posterior HOM-C gene , egl-5. Thus, a surprising diversity in HOM-C regulatory mechanisms e xists within a small set of cells even in a simple organism.