I4. Neural Crest Directed Gene Transfer Demonstrates Wnt1 Role in Mlanocyte Expansion and Differentiation during Mouse Development

Karen J. Dunn 1, Bart O. Williams2, Yi Li2 and William J. Pavan
1Genetic Disease Research Branch, National Human Genome Institute Research Institute,
2Division of Basic Sciences, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892-4472 USA

Wnt1 signaling has been implicated as one factor involved in neural crest-derived melanocyte (NC-M) development. Mice deficient for both Wnt1 and Wnt3a have a marked deficiency in trunk neural crest derivatives including NC-Ms (1). We have used cell lineage-directed gene targeting of Wnt signaling genes to examine the effects of Wnt signaling in mouse neural crest development. Gene expression was directed to cell-lineages by infection with subgroup A avian leukosis virus vectors (RCAS) (2) in lines of transgenic mice that express the retrovirus receptor tv-a (2). Transgenic mice with tva in either nestin expressing neural precuror cells (line Ntva) or dopachrome tautomerase (DCT) expressing melanoblasts (line DCTtva) were analyzed. We over-stimulated Wnt signaling in two ways: directed gene transfer of Wnt1 to Ntva+ cells and transfer of b-catenin to DCTtva+ NC-M precursor cells. In both methods, NC-M expansion and differentiation were effected. Significant increases were observed in the number of NC-Ms (melanin+ and tyrosinase related protein 1 (TYRP1) + cells), the differentiation of melanin- TYRP1+ cells to melanin+ TYRP1+ NC-Ms and the intensity of pigmentation per NC-M. These data are consistent with Wnt1 signaling being involved in both expansion and differentiation of migrating NC-Ms in the developing mouse embryo. The use of lineage-directed gene targeting will allow the dissection of signaling molecules involved in NC development and is adaptable to other mammalian developmental systems.