The experiments of this proposal are designed to understand how the eye and the forebrain from which it emerges are formed and patterned during embryonic development. We will analyze the role that two nuclear proteins - Vax1 and Vax2 - play in the specification of dorsal-ventral (top-bottom) position in the developing eye and forebrain. These transcription factors are induced in the anterior forebrain by Sonic hedgehog, a potent polarizing 'morphogen'that is ventrally expressed throughout the embryonic nervous system. We have discovered that the Vax proteins activate the expression of a gene - designated dnTcf7l2 - that acts as a strong antagonist of the Wnt proteins - a group of dorsal morphogens that normally oppose Sonic hedgehog. We will use genetic methods in frog and mouse embryos to assess the role the dnTcf7l2 plays in eye and forebrain development. We will use genetic and biochemical methods to identify the proteins that normally cooperate with the Vax proteins to regulate dnTcf7l2, and we will use high-throughput genome-wide screening assays to identify proteins that bind to the dnTcf7l2 regulatory region and activate its transcription. We already have two strong indications that dnTcf7l2 regulation and activity are important. First, the dnTcf7l2 regulatory region is among the most highly conserved DNA segments - as monitored by sequence change across vertebrate evolution - in the entire human genome. Second, frog embryos in which dnTcf7l2 activity is ablated from the beginning of embryogenesis lack both eyes and forebrains. These studies hold the promise of revealing fundamental new principles in the axial patterning of the nervous system.
Defects in neural patterning during embryogenesis can have severe ramifications with respect to brain malformations, developmental disorders, and learning deficits in children. It is therefore important to public health to understand fully the genetic, cell biological, and biochemical bases of brain patterning, as this knowledge opens the door to improved therapies for these debilitating childhood disorders.
|Slavotinek, Anne M; Chao, Ryan; Vacik, Tomas et al. (2012) VAX1 mutation associated with microphthalmia, corpus callosum agenesis, and orofacial clefting: the first description of a VAX1 phenotype in humans. Hum Mutat 33:364-8|
|Vacik, Tomas; Stubbs, Jennifer L; Lemke, Greg (2011) A novel mechanism for the transcriptional regulation of Wnt signaling in development. Genes Dev 25:1783-95|
|Kang, Kyung Hwa; Lemke, Greg; Kim, Jin Woo (2009) The PI3K-PTEN tug-of-war, oxidative stress and retinal degeneration. Trends Mol Med 15:191-8|