The Caenorhabditis elegans fate-determining gene mab-9 encodes a T-box protein required to pattern the posterior hindgut

Caenorhabditis elegans mab-9 mutants are defective in hindgut and male tail development because of cell fate transformations in two posterior blast ce lls, B and F. We have cloned mab-9 and show that it encodes a member of the T-box family of transcriptional regulators. MAB-9 localizes to the nucleus of B and F and their descendents during development, suggesting that it ac ts cell autonomously in the posterior hindgut to direct cell fate. T-box ge nes related to brachyury have also been implicated in hindgut patterning, a nd our results support models for an evolutionarily ancient role for these genes in hindgut formation.