9727443 CHIARAMELLO The general focus of this project is on the mechanisms that govern mammalian neuronal differentiation. Dr. Chiaramello will investigate the roles of the basic helix-loop- helix transcription factor ME1 during brain development. The ME1 gene encodes two isoforms of ME1, called ME1a and ME1b, due to alternative splicing of the messenger RNA. However, only the ME1a form is neuron-specific. Several lines of evidence suggest that ME1 plays an important role in the development of the nervous system: 1) It has a strong homology with transcription factors known to be essential for cell determination and differentiation in the nervous system, such as Drosophila gene Daughterless; 2) It is expressed in areas of the nervous system where neuronal differentiation and plasticity occur; 3) It is also detected in the subependymal region of the adult brain which includes constitutively proliferating cells (neural progenitor cells) as well as relatively quiescent cells that have the capacity to self- renew and give rise to neurons and glia; 4) It modulates the expression of two neuronal target genes involved in neuronal growth and development, GAP-43 and the low affinity nerve growth factor receptor p75LNGFR; and 5) It can assume distinct functions as a transcription factor, acting either as an activator or repressor. In this application, we propose experiments to further investigate ME1 with respect to its molecular mechanism of action and its neuron-specific partners during neuronal differentiation. The specific aims of this project are as follows: In specific aim I, Dr. Chiaramello will examine the posttranslational modification of ME1a during neuronal differentiation by assessing whether phosphorylation of ME1a by casein kinase II dictates the transcriptional activities of ME1 on neuronal target genes. In specific Aim II, Dr. Chiaramello will unravel the molecular mechanism of action of ME1a during neuronal differentiation. ME1a binds DNA as eit her a homodimer or heterodimer. The specificity of the genes regulated by ME1 are thought to depend on the dimerization partner. Therefore, it is of tremendous importance to identify the heterodimeric partners of ME1a. In specific Aim III, Dr. Chiaramello will analyze in detail the temporal and spatial expression of novel partners identified in Aim II. Results from the project will elucidate the cascade of regulatory events necessary for neuronal differentiation.
