Scratching the surface

Abstract

Mice with mutations at the steel locus (Sr) and the white spotting locus ( W) are phenotypically similar. They have a macrocytic anemia, are white or have a dilution of coat color, and have impaired fertility. SZ mutations result in abnormalities in stromal functions, such that migration of melanoblasts and hematopoietic stem cells is defective and the microenvlronrnent of tissues fails to support de- velopment of blood cells. In contrast, Wmutations have a primary e&t on the hematopoietic stem cell, germ cell, melanoblast and mast cell, rather than their tissue envi- ronments. On the basis of such data, it has been pos- tulated that the SZ locus encodes a llgand for a receptor encoded by the Wlocus. Following the discovery of the Wlocus receptor (c-Kit), several groups, using a variety of strategies, last year cloned and characterized the ligand for c-Kit [l-7], and provided evidence that the tissue lo- calization of the receptor and its ligand corresponds to the atkcted regions In Wand Sf mice, except that both are transcribed In the brain where no functional abnor- mality has been detected. The availability of the c-Kit lig- and (KL), which is also known as stem cell factor, mast cell growth factor and steel factor, has spurred a number of revealmg, If preliminary, studies of its function, which are the focus of this article.