The Regulation of Mammalian Development 
megacolon, as a result of the absence of enteric 
ganglia in the gut. Both melanocytes and enteric 
ganglia develop from the neural crest, a migrat- 
ing cell population that contributes to many cell 
types. By studying the s gene, we hope to gain 
insight into the genes that control the birth, mi- 
gration, and maturation of these cells. 
A high-density map around s is under way, us- 
ing mice carrying the original 5 mutation and an- 
other wild strain, Mus castaneus. In addition, 
the molecular studies are greatly aided by the 
many different mutant alleles of 5 created over 
the past 40 years at the Oak Ridge National Labo- 
ratory by William and Leane Russell. These al- 
leles, many of which are deletions, will be invalu- 
able in mapping the region on chromosome 14 
that contains the 5 gene. 
To gain insight into the nature of the 5 mutation, 
we are also comparing the behavior of neural crest 
cells in s-bearing and normal mice. For this pur- 
pose we have exploited a transgenic mouse strain 
carrying a (S-galactosidase gene that is expressed in 
early neural crest cells and their derivatives. To 
study later stages in melanocyte development, we 
are utilizing an antibody to the cell surface protein 
c-kit, which is expressed in these cells. We will 
thus identify the stage in neural crest development 
that the s mutation affects. 
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