ABSTRACT
Background The basic Helix loop helix (bHLH) family of transcription factors is one of the largest superfamilies of regulatory transcription factors and are widely used in eukaryotic organisms. They play an essential role in a range of metabolic, physiological, and developmental processes, including the development of the nervous system (NS). These transcription factors have been studied in many metazoans, especially in vertebrates but also in clades such as the cnidarians and sponges. However, nothing is known about their expression in the most basal bilaterian group, the xenacoelomorphs. Recently, our laboratory has characterized the full complement of bHLH in the genome of two members of the Xenacoelomorpha, the xenoturbellid X. bocki and the acoel S. roscoffensis. Understanding the patterns of bHLH gene expression in members of this phylum (in space and time) would provide us with new insights into the conserved roles of the bHLH and their putative specificitiesin this group. Our focus is on deciphering the specific roles that these genes have in the process of neurogenesis.
Results Here, we analyze the developmental expression of the whole complement of bHLH genes identified in the acoel S. roscoffensis. The members of bHLH class A seem to have specific conserved roles in neurogenesis, while other members of this and other classes have taken on more generalized functions. All gene expression patterns are described in embryos and early juveniles.
Conclusion Our results suggest that the main roles of the bHLH genes of S. roscoffensis are evolutionarily conserved, with a specific subset dedicated to patterning the nervous system: SrAscA, SrAscB, SrHes/Hey, SrNscl, SrSrebp,SrE12/E47 and SrOligo.