Evolution of Transcription Factors inCaenorhabditis

Abstract

Transcription factors (TFs) are regulatory proteins controlling gene expression by binding specific motifs associated with their target genes and playing essential roles during development and physiological response to stimuli. The evolution of transcriptional regulation is an important source of phenotypic diversity. The genome of the nematode Caenorhabditis elegans encodes a similar proportion of TFs as the human genome, although TF families show different patterns of expansion in human and in worm. The TF repertoire of C. elegans is well diversified with over 50 TF families. Alternative splicing and gene duplication contribute to the functional diversity of TFs and the rapid evolution of TF protein sequence suggests that TF evolution plays important roles in developmental evolution. Many of the principles that guided the diversification of the worm TFs are likely to be applicable to the evolution of TFs in other organisms. Key Concepts: The genome of C. elegans encodes 988 TFs belonging to 50 distinct families based on the type of DNA‐binding domain. The worm and human genomes encode a similar proportion of TFs, and in both species a third of the TFs show tissue‐specific gene expression. Alternative splicing increases the number of TF transcripts by 22%. Gene duplication contributes significantly to the functional diversification of TFs, and several examples illustrate the different evolutionary trajectories taken by TF duplicates. Tissue‐specific expression, alternative splicing, gene duplication and the combinatorial regulatory activity of TFs reduce the pleiotropic constraints operating on TF sequence evolution. TF factor sequence evolution plays an unappreciated role in developmental evolution. TFs can harbour high level of amino acid variation both between species and within populations.