Function of albinism gene oca2 in non-melanocyte cell development

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Project summary Loss of function mutations in the oculocutaneous albinism 2 (oca2) gene not only lead to defects in black pigment (melanin) synthesis important for skin color, but also increase the chances of developing “side” or “pleiotropic” effects. Some examples of pleiotropic effects include deficiencies in sensory or neural system development, as well as embryonic death depending on the identity of the mutated gene. Although pleiotropic effects are commonly observed in humans with hypopigmentation disorders like Waardenburg Syndrome and albinism, the underlying mechanisms are poorly understood primarily due to low sample size. Because pigment cells are easily viewed through transparent skin and eggs can be collected in high numbers year round, we propose to use zebrafish silver cells to better understand how pleiotropic effects arise. When oca2 is mutated, zebrafish larvae continue to make the correct number of black pigment cells, melanocytes, but melanin synthesis is severely decreased. Conversely, silver pigment cells do not express oca2, but are increased in number at stages following specification from neural crest. Using oca2 mutant iridophores as a model, we will address the following R03 specific aims: 1) Determine the iridophore developmental stages impacted by oca2 function. With aim 1 experiments, we will retest the role of oca2 in iridophore specification and examine iridophore development at multiple, additional stages including proliferation, differentiation and survival – all cellular events that could impact cell number; 2) Determine if oca2 directly or indirectly regulates iridophore number. Using our unique collection of melanocyte mutants, we will determine if oca2 directly (cell-autonomously) or indirectly (non- cell autonomously) regulates iridophore development. In additional experiments, we will conduct pilot [bulk and single cell RNA-Seq] analysis to determine if these methods can provide insight into oca2’s autonomous versus non-autonomous role during iridophore development. Specifically, these RNA-seq data will be analyzed to determine whether changes in the expression of intrinsic or extrinsic genes important for iridophore development occur with oca2 loss of function. Once these experiments are complete, we will have a characterized model for testing oca2 function in pleiotropic effects and a substantial amount of preliminary data for formulating hypotheses appropriate for R01 level research aimed at elucidating mechanistic connections between melanocytes/melanin and hearing/visual/skin system development in humans.