21.    Phenotypic and molecular characterisation of the depilated (Dep) hairloss mutation. 
Angela Waishan Lee (1), Ian Smyth (2), Rebecca Porter (3), Ian Jackson (1), Yoichi Gondo(4), Lisa Mckie(1),(1)MRC Human Genetics Unit, Edinburgh, UK (2)Keratinocyte Laboratory, CRUK London Research Institute, London, UK (3)Department of Dermatology, University of Cardiff, UK (4)Functional Genomics Research, RIKEN GSC, Kanagawa, Japan.

Depilated (dep) is an autosomal recessive mutation that is characterised by the loss of hair shortly after birth. Mutant mice can be identified by an unusually thin and short hair coat as early as a week of age when hairs first emerge from follicles. Adult hairs are greasy, matted and slightly depigmented. Previous studies using recombination assays have shown that dep is a defect of hair follicles due to deficiency of the epidermis rather than the dermis. Skin sections at successive time-points reveal acanthosis, intense pigment clumps at anagen, and dilated follicles at telogen which might promote the observed premature entry into 3rd anagen. Dep has been mapped by complementation analysis to a region of 160kb on mouse chromosome 4, within which Zdhhc21 is the most probable candidate based on sequencing data and published literatures that exclude the other 2 genes within the interval. Sequencing of Zdhhc21 in dep reveals a single amino acid deletion at residue 233 which is predicted to be intracellular. Zdhhc21 is a transmembrane zinc finger protein with DHHC-CRD (Asp-His-His-Cys-cysteine-rich domain) that belongs to a 23-member family. The function of Zdhhc21 is currently unknown but DHHC-CRD is hypothesized to be a palmitoyltransferase domain. To prove that Zdhhc21 is the gene responsible for dep, we are using transgenic rescue with a mouse BAC. To generate additional mutant alleles of Zdhhc21, a gene-based screen is being performed on archives of DNA samples from individual F1 ENU-mutagenised mice generated at the MRC Mammalian Genetics Unit and the RIKEN GSC respectively. Currently, we have isolated one mutation from the MRC archive which converts leucine to phenylalanine at a residue that lies immediately upstream of DHHC-CRD(L91F). Our RT-PCR data suggests that Zdhhc21 is ubiquitously expressed; whole-mount in-situ assay is being carried out to finely assess its expression pattern at embryonic stages.