Dorsal and Snail homologs in leech development

As part of an examination of how developmental mechanisms such as axis spec ification, cell fate specification, and segmentation have evolved, we have cloned homologs of the Drosophila melanogaster genes dorsal and snail from the glossiphoniid leech Helobdella robusta. Sequences from one dorsal-class gene (Hro-dl) and two snail-class genes (Hro-sna1 and Hro-sna2) were ident ified. Polyclonal antibodies were raised against the most conserved domains of HRO-DL and HRO-SNA1 Nuclear staining appeared for both proteins in mid- embryogenesis, in mesodermal and ectodermal precursors. During segmentation , segmentally iterated stripes of cells with strong HRO-DL staining appeare d. The stripes of HRO-DL staining were first concentrated in the cytoplasm of cells, and later in the nuclei. Around this time, HRO-SNA levels also ap peared in nuclei in segmentally iterated stripes. The localization of HRO-D L and HRO-SNA proteins raise the possibility that these genes are part of a conserved genetic pathway that, instead of specifying the dorsoventral axi s and the mesoderm as in flies, might play a role in the diversification of cell types within segment primordia during leech development.