The transcription factors HeBlimp and HeT-brain of an indirectly developing polychaete suggest ancestral endodermal, gastrulation, and sensory cell-type specification roles.

The expression of Blimp and T-brain was characterized during embryogenesis of the indirectly developing polychaete Hydroides elegans. The expression of both genes in the vegetal blastomeres of this lophotrochozoan is restricted to the lateral and oral regions of the blastopore. Both transcription factors also have expression patterns consistent with ancestral neural functions. HeBlimp is expressed in a couple of animal cap cells and exhibits a marked left bias that correlates with earlier development of the left eye in H. elegans. HeT-brain is expressed in animal cap blastomeres and eventually becomes restricted to apical tuft cells of early trochophore stages. The expression of Blimp and T-brain among directly and indirectly developing bilaterians suggests ancestral sensory cell-type specification, gastrulation by invagination, endoderm specification, mesoderm specification, and/or tripartite gut subdivision. These characterizations add to the long-term goal of understanding the regulatory evolution functions that underlies complex life cycles in metazoans. Copyright 2008 Wiley-Liss, Inc.