A Sea Cucumber Homolog of the Mouse T-Brain-1 is Expressed in the Invaginated Cells of the Early Gastrula in Holothuria leucospilota.

A cDNA clone for a sea cucumber T-box gene was isolated and characterized. Based on molecular phylogenetic analysis it is concluded that the putative gene Hl-Tbr, encoded by the cDNA clone, is a T-box gene of the T-brain subfamily and hence a homolog of the mouse T-brain-1 (Tbr-1) as well as of the Xenopus Eomesodermin. In situ hybridization analysis of whole mount specimens showed that Hl-Tbr was expressed in the invaginated cells at the early gastrula stage and the expression of the gene was scarcely detectable by the end of the late gastrula stage.