In C. elegans, the posterior Hox genes
php-3 and
nob-1, both abdominal-B (abd-B) homologs, play crucial patterning roles in both sexes during embryogenesis (Van Auken et al., 2000). An ongoing RNAi screen in our lab has also identified a specific role for these genes in patterning the development of the male tail tip during larval development. The male tail tip undergoes an interesting morphogenesis when the tail tip cells fuse, detach from the overlying cuticle, change shape and move anteriorly (Nguyen et al., 1999). A null allele of
php-3 (
ok919) results in a failure of tail tip morphogenesis. Similar phenotypes result from a new allele,
ny7, which changes a highly conserved aspartic acid to a tyrosine located within the homeodomain. A translational GFP fusion of PHP-3 constructed from the WT allele, but not from the
ny7 allele, partially rescues the tail tip phenotype of the
ok919 allele. This indicates that
ny7 is most likely a null. Both transgenes express variably in the tail tip and more broadly in the male tail. To test if PHP-3 functions cell autonomously to promote tail tip retraction we expressed
php-3 under the tail tip specific promoter from
lin-44. We find that PHP-3 is required in all four tail tip cells. Both
php-3 and
nob-1 are upstream of the transcription factor
dmd-3, as they positively regulate appropriate
dmd-3 expression levels. A conserved abd-B consensus site is present in a 1.1 kb region of the promoter of
dmd-3, termed the E(ht) enhancer. The E(ht) has previously been shown to be both sufficient and necessary for tail tip expression (Mason et al., 2008). We are currently investigating the possibility that PHP-3 and NOB-1 function by directly binding to these conserved domains within the E(ht) and enhance the expression of
dmd-3 during morphogenesis. Mason, D. A., Rabinowitz, J. S. and Portman, D. S. (2008).
dmd-3, a doublesex-related gene regulated by
tra-1, governs sex-specific morphogenesis in C. elegans. Development 135, 2373-82. Nguyen, C. Q., Hall, D. H., Yang, Y. and Fitch, D. H. (1999). Morphogenesis of the Caenorhabditis elegans male tail tip. Dev Biol 207, 86-106. Van Auken, K., Weaver, D. C., Edgar, L. G. and Wood, W. B. (2000). Caenorhabditis elegans embryonic axial patterning requires two recently discovered posterior-group Hox genes. Proc Natl Acad Sci U S A 97, 4499-503.