Fluorescent in situ hybridization reveals multiple expression domains for SpBrn1/2/4 and identifies a unique ectodermal cell type that co-expresses the ParaHox gene SpLox.

Here we report on the expression of two transcription factors previously reported to be involved in endodermal patterning, SpLox and SpBrn1/2/4. We describe three distinct domains of expression of the pou-domain gene SpBrn1/2/4. Endodermal expression of this gene is restricted to the foregut. SpBrn1/2/4 is also expressed in two distinct ectodermal domains: throughout the stomodeal ectoderm, and within cells scattered throughout the ciliated band. The ParaHox gene SpLox is demonstrated to also be expressed in ectodermal bilateral cell pairs in prism and early pluteus stage larvae. Double fluorescent in situ hybridization reveals that these cell pairs co-express both SpLox and SpBrn1/2/4, thus marking a novel cell type within the ciliary band of the sea urchin larvae.