Mutants in the
mab-9 ( m ale ab normal) gene have grossly deformed male tails lacking most internal structures. This phenotype results from a spatial transformation of the lineage of the major tail-specific blast cell B towards that of its anterior neighbour, Y, and a transformation of the blast cell F lineage towards that of its anterior neighbour U 1 . The role of
mab-9 during development therefore is to distinguish the fate of B from that of Y, and likewise F from U, giving these cells their spatial identity. In the hermaphrodite, B forms part of the structure of the rectum:
mab-9 mutant hermaphrodites have rectal abnormalities and are constipated. Therefore,
mab-9 can be viewed as functioning both in the development of the hermaphrodite hindgut and the male tail in C. elegans . We have cloned
mab-9 by fine mapping and transformation rescue and find that
mab-9 encodes a member of the T-Box family of transcription factors, the prototype of which, Brachyury , was first identified as a mutation disrupting tail development in mouse 2 . The Drosophila homologue, brachyenteron , is required for hindgut formation 3 .
mab-9::GFP localises to the nucleus and is expressed in B and F lineages during larval development. Inappropriate expression of
mab-9 can result in embryonic lethality, suggesting that the expression of
mab-9 has to be tightly controlled during development. Progress towards the identification of
mab-9 regulators and targets will be presented and the possible evolutionary significance of
mab-9 will be discussed. 1 Chisholm and Hodgkin, Genes Dev ., 3 : 1413-1423, 1989 2 Dobrovolskaia-Zavadskaia, C R Sceances Soc. Biol ., 97 : 114-116, 1927 3 Kispert et al ., Genes Dev ., 8 : 2137-2150, 1994. Singer et al., Development , 122 : 3707-3718, 1996