Mouse models in cutaneous biology

The recent advent of large scale reverse genetics and phenotyping projects has signalled a new era in the application of mouse genetics to understand gene function. International efforts to elucidate gene function are exemplified in The Sanger Mouse Genetics Project. This project has created a genetically mutant mouse resource of unprecedented size for the phenotype-based investigation of gene function in vivo. The integration of organ- specific screening pipelines is critical for the continued existence and maximization of reverse screening efforts to ascribe gene function. Using this approach, the analysis of the genetic complement to skin biology is examined. Phenotype data gathered as a part of this screen initiated the in depth investigation of the contribution of two genes, Krt76 and Mad2, to skin barrier function and skin stem cells, respectively. This is the first and largest tissue-specific reverse genetic screen ever to be carried out, and accordingly, has identified novel genes and novel roles for known genes required for normal skin function. At the genome level, a multi-test, multi-parameter reverse genetic screen was applied to over 500 different knockout mouse strains with the aim of identifying defects in development or homeostasis of the skin. The dynamic, indispensable, and accessible nature of the skin make it a valuable model system in which to study genetic contributions to its function and model cell biology. This screen identified more than 20 different affected lines, many of which carry mutations in genes that have not previously been implicated in the biology of the organ. This work highlights the promise of high throughput reverse genetic screens to give critical insights into the genetics of skin biology. The regenerative properties of the skin are regulated by multiple stem cell populations that reside there, making the skin an excellent organ in which to model stem cell biology. Mad2 is a known component of the spindle assembly checkpoint (SAC) whose loss in mitotically active cells leads to aneuploidy. Because aneuploidy and disruptions in spindle assembly are incompatible with early mouse development, Mad2 was conditionally inactivated in the skin. This allowed for the in vivo investigation of Mad2, and showed that defects in the checkpoint are tolerated in the dividing cells of the interfollicular epidermis, but not in the stem cell population in the hair follicle. This study is an elegant example combining mouse genetics and skin biology to understand the differential response to aneuploidy within a single tissue. The healing and protective properties of the skin were examined using germline inactivation of Keratin76 (Krt76). It was shown that Krt76, a poorly characterized intermediate filament protein, is absolutely required to maintain the integrity of the skin and is essential for postnatal survival. The progressive development of cutaneous wounds occurs on the background of a primary defect in the maintenance of the skin barrier. Here, a novel mechanism by which intermediate filaments interact with tight junction components to maintain barrier function in the skin is described