Melanocyte Development in Danio rerio

The study of pigment patterns in zebrafish (Danio rerio) is an exciting aspect of developmental biology. Zebrafish contain three distinct types of pigment. Xanthophores create the yellow pigment easily seen in the fin, iridiphores form the reflective pigments and are near the head and over the stomach, and black pigmented melanocytes form the stripes along the body and caudal fin. The wild-type zebrafish has four horizontal melanocyte stripes across its body as well as three horizontal melanocyte stripes across its caudal fin.

One way to study pigment pattern is to look at re-establishment of the pigment pattern in regenerating fins. pyewacket, a mutant, differs from wild-type in that pye regenerating fins have more melanocytes than wild-type regenerating fins. One hypothesis is that the pye gene tells melanocyte stem cells the correct number of melanoblasts (which differentiate immediately into melanocytes) and stem cells to make. Thus, in pye mutants, the allocation between melanoblast and stem cell fates may be disrupted, and many more melanoblasts than stem cells are made .

I am interested in the analysis of the relationship between the genotype and phenotype of the pyewacket mutant, since pyewacket could eventually tell us many things about the development and requirements of stem cells. The ultimate goal of my research was to isolate the gene. It was already known that pyewacket is on linkage group one, and it was my aim for the summer to find markers that closely flanked each side of the gene.

I began by identifying markers that could distinguish between the inbred strains SJD and C32. The pye mutation was generated in the C32 background, and pye individuals were crossed to SJD fish for mapping. I then sorted individuals from a mapping cross for having the pye phenotype or wild-type phenotype, and I then isolted DNA from these individuals. Using this DNA, I found the number of recombination events between each marker and the pye mutation, and ordered these markers with respect to each other and the pye mutation. In this way I identified the closest markers on either side of the pye mutation. My data helped to reduce the area in which pyewacket could be located, yet more research is necessary to successfully isolate the gene.