Mice with a Targeted Mutation of Patched2 Are Viable but Develop Alopecia and Epidermal Hyperplasia

Abstract

Hedgehog (Hh) signaling plays pivotal roles in tissue patterning and development in Drosophila melanogaster and vertebrates. The Patched1 (Ptc1) gene, encoding the Hh receptor, is mutated in nevoid basal cell carcinoma syndrome, a human genetic disorder associated with developmental abnormalities and increased incidences of basal cell carcinoma (BCC) and medulloblastoma (MB). Ptc1 mutations also occur in sporadic forms of BCC and MB. Mutational studies with mice have verified that Ptc1 is a tumor suppressor. We previously identified a second mammalian Patched gene, Ptc2, and demonstrated its distinct expression pattern during embryogenesis, suggesting a unique role in development. Most notably, Ptc2 is expressed in an overlapping pattern with Shh in the epidermal compartment of developing hair follicles and is highly expressed in the developing limb bud, cerebellum, and testis. Here, we describe the generation and phenotypic analysis of Ptc2^tm1/tm1 mice. Our molecular analysis suggests that Ptc2^tm1 likely represents a hypomorphic allele. Despite the dynamic expression of Ptc2 during embryogenesis, Ptc2^tm1/tm1 mice are viable, fertile, and apparently normal. Interestingly, adult Ptc2^tm1/tm1 male animals develop skin lesions consisting of alopecia, ulceration, and epidermal hyperplasia. While functional compensation by Ptc1 might account for the lack of a strong mutant phenotype in Ptc2-deficient mice, our results suggest that normal Ptc2 function is required for adult skin homeostasis.

Supplemental material for this article may be found at http://mcb.asm.org/.

We thank S. Yu for technical assistance and A. E. Oro (Stanford University) for providing the Ptc1^−/− embryonic fibroblast cells.

E.N. and P.B. were supported through a studentship, fully or in part, by the Ontario Student Opportunity Trust Fund-Hospital for Sick Children Foundation Student Scholarship Program. This work was supported by funds from the National Cancer Institute of Canada to C.-C.H.