Multiple retinoic acid pathway factors function together during development of a mollusc

In developing chordate embryos, the retinoic acid (RA) pathway is involved in many key developmental patterning systems. Recently, it has become clear that at least some components of the RA pathway are more ancient than chordates. However, the participation of these components in an RA pathway, and the role of such a pathway in developing non-chordate embryos remain unclear. Here, we demonstrate the presence of an extensive set of RA pathway components in the genome of the mollusc Tritia obsoleta, and examine their expression using in situ hybridization. We then examined the function of multiple RA pathway genes using RA treatments, drug treatments and morpholino (MO) knockdowns. These manipulations impacted a similar set of structures in development, especially the shell and the digestive tract, indicating that the retinoic acid pathway is functional in Tritia. Together, this is the most comprehensive evidence yet for an RA signaling pathway functioning in embryogenesis of a non-chordate.