Out on a LIM: LIM homeobox genes in the ctenophore Pleurobrachia bachei

Abstract

LIM homeobox (Lhx) gene family consists of six subfamilies of patterning genes which play a major role in the development of the nervous system and are found only in animals. We looked at their presence and expression in the ctenophore Pleurobrachia bachei to study their evolution and development. Ctenophores are among the most basal metazoans and one of the first animals to have a nervous system. We found four Lhx genes in P. bachei, Lhx1/5, Lhx3/4, Islet and Lmx, with our gene prediction models. Lhx2/9 and Lhx6/8, the other two subfamilies in most metazoans, were absent. None of these genes would clone using an adult cDNA library but Lhx3/4 and Lmx were successfully cloned using an embryonic cDNA library. Ctenophores and sponges are the only taxons that have four Lhx gene families instead of six. According to this genomic data, ctenophores and sponges are the most basally branched metazoans. Further research will be needed to understand the role that the Lhx gene family plays in the evolution and development of nerves in ctenophores.