Douglas T. Kohn, Ph.D.

     The expression of the growth associated protein GAP-43 coincides with the development and regeneration of neural connections, although high levels persist in areas associated with synaptic plasticity and long term potentiation (LTP), such as the hippocampus and entorhinal cortex.  Using the expression of GAP-43 as a model, my research focuses on the posttranscriptional control of gene expression during nervous system development.  The 3' untranslated region (UTR) of GAP-43 mRNA is highly conserved in evolution and predicted to form stemloop structures.  Previous studies have shown that it contains cis-acting elements that are required for its selective stabilization in response to growth-factors, such as nerve growth factor (NGF).  The GAP-43 3' UTR is also recognized by several brain-specific RNA-binding proteins.  One of these proteins, HuD is a member of a neuron-specific family of RNA-binding proteins believed to participate in the processing of mRNAs involved CNS development.  HuD contains three RNA recognition motifs (RRMs) as well as domains that mediate protein-protein interactions.  Therefore, HuD may recognize distinct RNA secondary structures and selectively recruit different proteins to task-specific ribonucleoprotein (RNP) particles.  Current studies in my lab are aimed at characterizing the molecular mechanisms controlling the formation and function of these RNP particles.  My preliminary results (see figure) indicate that the degradation of GAP-43 mRNA during development can be reproduced in vitro .  Using a variety of molecular biology techniques (e.g. RT-PCR, RNA-protein binding assays, northern and western blot analysis) in conjunction with tissue fractionation, I intend to isolate and characterize developmentally regulated trans-acting factors and assay their effect on the degradation of GAP-43 mRNA in vitro.

Selected References:

• Chung, S., N.I. Perrone-Bizzozero, D.T. Kohn and H. Furneaux (1997) The elav-like proteins bind to a conserved regulatory element in the 3'-untranslated region of GAP-43 mRNA.  J. Biol. Chem. 272:6593-6598.

• Tsai, K.-C., V.V. Cansino, D.T. Kohn, R.L. Neve, and N.I. Perrone-Bizzozero (1997) Post-transcriptional regulation of the GAP-43 gene during neuronal differentiation by specific sequences in the 3' untranslated region of the mRNA.  J. Neurosci 17:1950-1958.

• Kohn, D.T., K.-C. Tsai, R. Thompson, V.V. Canisino, R.L. Neve and N.I. Perrone-Bizzozero (1996) Role of Highly Conserved Pyrimidine-rich Sequences in the 3'  Untranslated Region  of the GAP-43 mRNA in mRNA stability and RNA-protein interactions.   Mol. Brain Res. 36:240-250.

• Kohn, D.T. and N.I. Perrone-Bizzozero (1994) Binding of brain cytosolic proteins to the GAP-43 mRNA.  J. Neurochem. 62:S14C (Suppl.)

• Perrone-Bizzozero, N.I., V.V. Cansino and D.T. Kohn (1993) Posttranscriptional regulation of GAP-43 gene expression in PC12 cells through protein kinase C-dependent stabilization of the mRNA.  J. Cell. Biol. 120:1263-1270.