A NLRR-1 gene is expressed in migrating slow muscle cells of the trout (Oncorhynchus mykiss) embryo

NLRR-l (neuronal leucine-rich repeat-l) is a transmembrane protein that functions as a cell adhesion molecule regulating morphogenesis. A previous study in the mouse reported that the somitic expression of NLRR-1 is restricted to the dorsal lip of the dermomyotome that gives rise to the epaxial muscle. In this study, we report the expression of a NLRR-1 gene in the trout-developing somite. Whole mount in situ hybridization showed that NLRR-l transcript accumulated in a rostro-caudal wave in the adaxial slow muscle cells, which are initially found deep in the somite, immediately adjacent to the notochord. No labelling was observed in the segmental plate from which somites form. As somites mature along an anteroposterior axis, the NLRR-l-positive adaxial cells exhibited an apparent migration radially to the lateral surface of the myotome where they ultimately form the peripheral slow muscle fibres. These observations show that a NLRR-1 gene is expressed in a subpopulation of myogenic cells of the trout embryo, but the anatomical location and the fate of this subpopulation are distinct from those of the NLRR-1 positive myogenic cells in amniotes. NLRR-l was also transcribed in distinct areas of the developing nervous system including the telencephalon, the optic tectum, the cerebellum, the neural tube, the retina, and the branchial arches.