ROLE OF ALPHAE-CATENIN IN REGULATION OF BRAIN SIZE AND BRAIN CANCER

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Cell adhesion and polarity are critical for normal development and loss of adhesion and polarity are the hallmarks of cancer. During mammalian brain development neural progenitor cells monitor and adjust their rates of proliferation to produce organ of predetermined size. Progenitors are highly polarized. They contain distinct apical membrane domains, which are lining the brain ventricles, and basolateral membrane domains. A prominent cell-cell adhesion structure called apical junctional complex separates these two membrane compartments. To determine the role of apical junctional complexes in neural progenitor cells we ablated these structures in embryonic progenitors using conditional deletion of essential adherens junction gene, alphaE-catenin. We found that mutant animals show severe brain dysplasia and hyperplasia and efficiently double total brain cell numbers at the time of birth. Microarray analysis of the alphaE-catenin-/- brains revealed activation of the sonic hedgehog (SHH) pathway. Inhibition of SHH signaling in developing embryos in vivo did not stop proliferation but eliminated the differences in proliferation between the wildtype and mutant cells revealing causal role of SHH activation in alphaE-catenin-mediated hyperplasia. Thus, we found that alphaE-catenin connects cell-density-dependent adherens junctions with the developmental hedgehog pathway and that this connection may provide a negative feedback loop controlling the size of developing mammalian brain. To reveal the molecular mechanisms connecting alpha-catenin with the SHH pathway we propose to determine alpha-catenin interacting partners and analyze the activity of these proteins in the hedgehog signaling. For this purpose we will develop the protocol for two-step purification of alpha-catenin-containing protein complexes and Mass Spec identification of proteins present in this complex.