Grey, a novel mutation in the murine Lyst gene, causes the beige phenotype by skipping of exon 25

The murine beige mutant phenotype and the human Chediak-Higashi syndrome are caused by mutations in the murine Lyst (lysosomal trafficking regulator) gene and the human CHS gene, respectively. In this report we have analyzed a novel murine mutant Lyst allele, called Lyst, that had been found in an ENU mutation screen and named grey because of the grey coat color of affected mice. The phenotype caused by the Lyst mutation was inherited in a recessive fashion. Melanosomes of melanocytes associated with hair follicles and the choroid layer of the eye, as well as melanosomes in the neural tube-derived pigment epithelium of the retina, were larger and irregularly shaped in homozygous mutants compared with those of wild-type controls. Secretory vesicles in dermal mast cells of the mutant skin were enlarged as well. Test crosses with beige homozygous mutant mice (Lyst ) showed that double heterozygotes (Lyst/Lyst ) were phenotypically indistinguishable from either homozygous parent, demonstrating that the ENU mutation was an allele of the murine Lyst gene. RT-PCR analyses revealed the skipping of exon 25 in Lyst mutants, which is predicted to cause a missense D2399E mutation and the loss of the following 77 amino acids encoded by exon 25 but leave the C-terminal end of the protein intact. Analysis of the genomic Lyst locus around exon 25 showed that the splice donor at the end of exon 25 showed a T-to-C transition point mutation. Western blot analysis suggests that the Lyst mutation causes instability of the LYST protein. Because the phenotype of Lyst and Lyst mutants is indistinguishable, at least with respect to melanosomes and secretory granules in mast cells, the Lyst mutation defines a critical region for the stability of the murine LYST protein. © Springer Science+Business Media, Inc. 2006.