Identification of novel genes including Dermo-1, a marker of dermal differentiation, expressed in trout somitic external cells.

The external cell layer that surrounds the fish primary myotome provides the myogenic precursors necessary for muscle growth, suggesting that this epithelium is equivalent to the amniote dermomyotome. In this study we report the identification of a trout orthologue of the dermal marker Dermo-1, and show that trout somitic external cells, which are all potentially myogenic as indicated by the transcription of Pax7 gene, express Dermo-1. This finding and our previous observation that external cells express collagen I show that these cells have dermis-related characteristics in addition to exhibiting myogenic features. In an effort to identify novel genes expressed in the external cell epithelium we performed an in situ hybridisation screen and found both collectin sub-family member 12, a transmembrane C-type lectin, and Seraf, an EGF-like repeat autocrine factor. In situ hybridisation of staged trout embryos revealed that the expression of Dermo-1, collectin sub-family member 12 and Seraf within the external cell layer epithelium was preceded by a complex temporal and spatial expression pattern in the early somite.