Microphthalmia and Loss of Coat Pigmentation from Transgenic Expression of a Neurogenic Factor in Pigment Cell Precursors.

Abstract

A neuronal determination factor was expressed in the developing melanocyte lineage to explore determinants of melanocyte development from the neural crest. Transgenic mice expressing the neurogenic bHLH factor MASH-1 from the dopachrome tautomerase (Dct) promoter were generated using a 3.2 kb fragment of Dct upstream regulatory sequence linked to a FLAG epitope-tagged version of the murine Mash1 gene. A single microphthalmic founder with a mosaic coat color phenotype produced non-pigmented, microphthalmic F1 progeny. The F1 progeny transmitted the transgene with approximately 50% frequency to F2 progeny that shared the phenotype. Analysis of the eye of transgenic embryos at E11.5 revealed the presence of a developing lens and neuroretinal layer. However, the structure corresponding anatomically to the location of the retinal pigmented epithelium (RPE) was supplanted by a non-pigmented layer, termed RPE-like layer, that is more than one cell thick. At E14.5, the neuroretina is elongated, and the RPE-like layer extends anterior to the lens, forming a single continuous structure when examined in transverse sections. The ocular and coat color phenotypes of the Dct::Mash1 transgenic line demonstrate that expression of Mash1 in pigment cell precursors alters the development or differentiation of both non-neural crest-derived cells of the RPE and neural crest-derived melanocytes. These alterations result in the failure of proper eye development and in a dominantly inherited mutant coat color phenotype, respectively.