Activation of the Receptor Tyrosine Kinase Kit Is Required for the Proliferation of Melanoblasts in the Mouse Embryo

Abstract

The development of neural crest-derived melanocytes, as well as haematopoietic and germ cells, is affected by mutations of the Kit and Mgf genes, which lead to dominant spotting (W) or steel (Sl) phenotypes. Mgf codes for the ligand of the receptor tyrosine kinase encoded by the Kit locus. KitW-v, a point mutation exerting a dominant negative effect, causes a substantial reduction in tyrosine kinase activity of the Kit receptor and leads to a characteristic pigmentation phenotype, namely dilute coat colour and a white ventral and head spot with reduced pigmentation of the feet and tail in the heterozygous animal, as well as slight anaemia. Homozygous animals lack coat pigmentation and are severely anaemic and infertile. Dct is a marker for cells of the melanoblast lineage. In order to study these cells in detail we have generated transgenic mouse lines carrying the lacZ reporter under the control of the Dct promoter and have used the embryonic expression of the reporter to identify early melanoblasts before they begin to produce pigment. Our transgenic lines have simplified the study of melanoblasts in the mouse embryo, and by crossing our mice with KitW-v mutants we have been able to identify the midgestation stages at which melanoblasts rely critically on Mgf/Kit interactions. We conclude that the survival of immature melanoblasts depends crucially upon Kit signalling up until E11, and later in development Kit plays a vital role in melanoblast proliferation. Our data do not describe a dependence upon Kit for melanoblast migration or differentiation.

RBP-Jκ-dependent Notch signaling enhances retinal pigment epithelial cell proliferation in transgenic mice

“…Although many tumor cells were negative for RPE65, the marker of terminally differentiated RPE cells, some cells, especially in the pigmented areas of the tumors, expressed Pmel17, a marker of premelanosomes (Supplementary Figure S6). Furthermore, X-gal staining of eye sections from Tyrp1::NotchIC/1; Dct::LacZ/1 mice (Mackenzie et al, 1997) confirmed that the cells forming the pigmented mass in eyes were from RPE origin (Figure 3d). …”

Effects of G-protein mutations on skin color

“…We maintained Kit w-v and Pax3 Splotch mice on a C57 background and Ednrb s-l mice on a SSL/Le background. We crossed mice carrying the Dct-lacZ reporter transgene (provided by M. Shin (Fox Chase Cancer Center, Philadelphia, Pennsylvania, USA) with the permission of I. Jackson (MRC Human Genetics Unit, Western General Hospital, Edinburgh, Scotland)) 24 for at least three generations to C3HeB/FeJ mice. All experiments were carried out under a protocol approved by the Stanford Administrative Panel on Laboratory Animal Care.…”

“…Many white-spotting mutations are thought to act by compromising the proliferation or survival of melanoblasts, such that progenitor pools are exhausted before migration is complete [23][24][25][26] . If this is the case, the increased number of early melanoblasts caused by Dsk1 and Dsk7 mutations might rescue white spotting, regardless of the underlying cause.…”

Malignant melanoma: genetics and therapeutics in the genomic era

“…The geographic separation between follicular melanocyte stem cells (bulge region) relative to their differentiated progeny (hair bulb) permitted relatively simple quantitative analysis of each population. Using transgenic mice in which the melanocyte lineage was tagged by LacZ (Mackenzie et al 1997), it was observed that senile graying is associated with progressive depletion of the stem cell pool (Nishimura et al 2005). Melanocyte stem cell depletion was preceded by the stochastic appearance of pigmented melanocytes within the bulge region-a population that was not maintained, suggesting that it may represent a dead-end route away from the stem cell pool.…”