Role of Pitx3 signaling cascades in the regulation of Xenopus eye, laterality and somite development

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We started by studying the network of genes that contribute to normal eye development and maintenance, specifically the role of a regulatory gene, pitx3, in the formation of lens. Our interests expanded to visceral organ asymmetry and vertebral development when it became apparent that pitx3 plays a role in these aspects of development too. This gene is linked to eye and neurological deficits in mice and humans. The preservation of nearly identical roles for this gene in eye, and in eye gene networks, means that experiments in organisms such as frog offer big benefits to understanding development in mammals such as ourselves. For example, frog embryos develop externally (no uterus to get in the way of observation and experimentation), they can be easily manipulated surgically or genetically, and the century-long eye studies in amphibians have pioneered and clarified our understanding of how eyes develop in human. ******In our studies of pitx3, we previously showed how it plays a primary role in the formation of lens, which is in turn critical to formation of the retina. The absence of frog pitx3 activity, no lens forms, and retinal development is either impaired or prevented. We then developed a new procedure to examine how this gene regulates others in the network of genes that build an eye. Our system works with exquisite sensitivity to reveal gene regulatory changes on a cell-by-cell basis: we identified some new and important players that are regulated by pitx3, but that are not yet well understood in human eye development. ******A curious feature of pitx3 function is that it can turn target genes on or off in a context-dependent manner. Our proposal is to look for pitx3-interacting partners that might explain this flexibility. Moreover, by cataloging the interacting partners (interactome) of pitx3, we might come to understand: how it affects development of vertebral precursors and heart; whether there are differences in partner availability and timing between humans and frogs; and we might identify new partners with mammalian relatives. For example, since one of the mutational effects of pitx3 is to produce lens cataracts, and pitx3 activates at least one of the genes that provides the bulk of protein constituting and defining the clarity of lens (a beta-crystallin gene), our proposal to identify interacting partners will improve our understanding and reveal some of the mechanisms that underly cataract formation. An additional feature of pitx3 activity is that in frog, it plays a role in defining the asymmetry of some of the visceral organs such as heart, gastro-enteric tract etc. Pitx3 dysfunction results in inversion of organ placement, e.g.; patterning defects of heart, vasculature, and gut. Since related genes play a role in organ asymmetry in human, our search for interacting partners in frog has potential to illuminate new avenues for investigation of human congenital heart defects.