Characterization and developmental expression of xSim, a Xenopus bHLH/PAS gene related to the Drosophila neurogenic...

We have isolated a novel gene from Xenopus, denominated xSim, which encodes a protein of 760 amino acids containing a basic helix-loop-helix (bHLH) motif contiguous to a PAS domain characteristic of an emerging family of transcriptional regulators so called bHLH/PAS. xSim shares a strong amino acid sequence identity with the Drosophila Single-minded (dSim) and with the murine Sim1 and Sim2 proteins. Phylogenetic analysis reveals that xSim gene is an ortholog gene of the mSim2 gene. Spatio-temporal analysis shows a maternal and a zygotic expression of xSim throughout early Xenopus development. In situ hybridization assays reveal that the transcripts are enriched in the animal hemisphere until blastula stage and extend to the marginal zone at early gastrula stage. As development proceeds, xSim is mainly restricted to the central nervous system.