PHYSICAL MAPPING OF THE TEC AND GABRB1 LOCI REVEALS THAT THE W-SH MUTATION ON MOUSE CHROMOSOME-5 IS ASSOCIATED WITH AN INVERSION

In the mouse, mutations in the c-Kit proto-oncogene, a member of the r eceptor tyrosine kinase (RTK) gene family, have pleiotropic effects on hematopoiesis, pigmentation and fertility (dominant spotting, W). How ever, in the W-sh allele the defect is confined to abnormal pigmentati on caused by the disruption of 5' regulatory sequences of Kit leaving an intact structural gene. In this report, the previously published ph ysical map around the Pdgfra-Kit-Flk1 RTK loci is extended by mapping the loci encoding the GABA(A) (gamma-aminobutyric acid) receptor subun it beta 1, Gabrb1 and a cytoplasmic kinase (Tec) 3 Mb proximal to Kit. PFGE analysis of the wild-type (C57BL/6J) chromosome demonstrates the following gene order: cen-Gabrb1-Tec-Pdgfra-Kit, whereas the analysis of W-sh/W-sh DNA is consistent with the order: cen-Gabrb1-Pdgfra-Tec- Kit. This altered physical map can be explained by an inversion on the W-sh chromosome located proximally to the Kit locus and spanning the 2.8 Mb Pdgfra-Tec chromosomal segment. This high resolution physical m apping study identifies large DNA fragments that span the two inversio n breakpoints and potentially carry Kit upstream regulatory elements i nvolved in the control of Kit expression during embryonic development.