Project Summary/Abstract Mendelian variation in pigmentation is a rich genetic resource to identify and study signaling pathways relevant to human biology, but the repertoire of mutations that affect pigmentation in mice and in humans coat color has become saturated. Advances in genome sequencing technology now extend the reach of forward genetics beyond humans and model organisms to domestic and wild animals, for which there are many pigmentary phenotypes likely to represent conserved signaling pathways but whose molecular basis is unknown. Using pigmentary variation in domestic cats, our research group discovered a striking connection between a novel transmembrane protease encoded by Transmembrane aminopeptidase Q (Taqpep) and a secreted Wnt inhibitor encoded by Dickkopf 4 (Dkk4). Initial studies of Taqpep knockout mice reveal a role in multiple cell types and tissues including hair, the enteric nervous system, and the palate. In a different non-model organism, the plains zebra, Taqpep is a candidate gene for aberrant striping in an isolated population in Rwanda. Our results point to a central role for Taqpep in pathways and tissues that are directly relevant to human biology and disease, but a molecular understanding of those pathways is most effectively approached by combining forward genetics for gene discovery in non-model mammalian organisms with experimental genetics in laboratory mice and studies in cultured mammalian cells. We propose to: (1) Identify additional components of Taqpep action by forward genetics in (A) Bengal cats and (B) plains zebras. (2) Investigate and compare the action of Taqpep and Dkk4 in laboratory mice. (3) Determine when, where, and how Taqpep acts in vivo.