BOWEL, AN ODD-SKIPPED HOMOLOG, FUNCTIONS IN THE TERMINAL PATHWAY DURING DROSOPHILA EMBRYOGENESIS

The terminal genes of Drosophila specify nonsegmented regions of the l arval body that are derived from the anterior and posterior regions of the early embryo. Terminal class genes include both maternal-effect l oci (typified by the receptor tyrosine kinase torso) that encode compo nents of a signal transduction cascade and zygotic genes (e.g. tailles s and huckebein) that are transcribed at the poles of the embryo in re sponse to the local activation of the pathway. We have characterized a zygotic gene, bowel, that was identified as a zinc finger homolog of the pair-rule segmentation gene odd-skipped. bowel transcripts are ini tially expressed at both poles of the blastoderm embryo and in a singl e cephalic stripe. This pattern depends upon torso and tailless activi ty, but is not affected in huckebein mutants. We isolated and sequence d five mutations that affect the bowel protein, including a nonsense m utation upstream of the zinc fingers and a missense mutation in a puta tive zinc-chelating residue. bowel mutants die as late embryos with de fects in terminal derivatives including the hindgut and proventriculus . Our results indicate that the developmental roles of odd-skipped and bowel have diverged substantially, and that bowel represents a new me mber of the terminal hierarchy that acts downstream of tailless and me diates a subset of tailless functions in the posterior of the embryo.