David L. Turner, Ph.D.
Associate Research Professor
Associate Professor, Dept of Biological Chemistry

5051 BSRB
109 Zina Pitcher Place
Ann Arbor, MI 48109-2200

dlturner@umich.edu

(734) 647-6890

Current Research Interests:

Research in my laboratory is focused on the molecular mechanisms that regulate neurogenesis in vertebrates. Areas of interest include the regulation of neuron formation by neural basic-helix-loop-helix (bHLH) transcription factors, the role of microRNAs in neural development, and the use of expression vectors for RNA interference (RNAi).

Neural bHLH transcription factors such as MASH1, neurogenin, and neuroD1 are required for the formation and survival of subsets of neural progenitor cells and/or differentiated neurons in a variety of organisms. Forced expression of neural bHLH proteins is sufficient to direct ectodermal or other competent cells to differentiate into neurons in a variety of model systems. These observations indicate that bHLH proteins play a central role in the regulation of neuronal differentiation. In addition, neural bHLH proteins contribute to the determination of neuronal identity in both the peripheral and central nervous systems. We have developed a cell culture model in which uncommitted mouse P19 embryonal carcinoma cells can be directed to differentiate as neurons in response to transient expression of neural bHLH proteins. In response to neural bHLH expression, P19 cells exit the cell cycle, adopt a neuronal morphology, and express a variety of neural specific proteins. We are using P19 cells, primary cortical neural progenitors, and other in vitro and in vivo models to study neural bHLH function. We are particularly interested in how neural bHLH proteins direct cell cycle exit. In addition, we are using microarray analysis and RNAi to identify genes that function downstream of the neural bHLH proteins to direct neuronal differentiation.

Neuronal differentiation of mouse P19 cells transiently transfected with
an expression vector for the neural bHLH protein neurogenin2. Tranfected cells
are labeled with green flourescent protein (GFP, top). Transfected cells express
a neuron-specific beta-tubulin III protein (TuJ1. bottom).

MicroRNAs (miRNAs) are small endogenous RNAs (~22nt) that are thought to function as negative regulators of translation and/or RNA stability. Numerous miRNAs are expressed in the adult nervous system, and many of these are expressed during development as well. We are interested in determining the spatial expression patterns of miRNAs in the developing mammalian nervous system. Understanding the expression patterns of miRNA should help to identify miRNAs that participate in the regulation of neuronal differentiation and/or identity. In addition, we are using molecular approaches to analyze the functional role of specific miRNAs during neurogenesis and neuronal differentiation.

We have constructed vectors for the expression of short hairpin RNAs (shRNAs) in mammalian cells, using a mouse U6 snRNA promoter. The shRNAs can be used to target cellular mRNAs for destruction in a sequence-specific manner, providing a useful tool for analyzing gene function. More recently, we have constructed vectors for RNAi based on the mammalian miR-155 miRNA precursor, and we are using these vectors to assess the role of transcription factors and signaling molecules during neuronal differentiation.

Selected Publications:

Farah, M. H., Olson, J. M., Sucic, H. B., Hume, R. I., Tapscott, S. J., and Turner, D. L. (2000). Generation of neurons by transient expression of neural bHLH proteins in mammalian cells. Development: 127, 693-702.

Yu, J-Y., DeRuiter, S. L., and Turner, D. L. (2002). RNA interference by expression of short-interfering RNAs and hairpin RNAs in mammalian cells. Proc. Natl. Acad. Sci. USA, Vol. 99: 6047-6052.

Yu,J-Y., Taylor, J., DeRuiter, S., Vojtek, A. B., and Turner, D. L. (2003). Simultaneous inhibition of GSK3 a and GSK3 b using hairpin siRNA expression vectors. Molecular Therapy 7: 228-236.

Vojtek, A. B., Taylor, J., DeRuiter, S., Yu, J-Y., Kwok, R. P. S., and Turner, D. L. (2003). Akt regulates basic helix-loop-helix transcription factor-coactivator complex formation and activity during neuronal differentiation. Molecular and Cellular Biology 23: 4417-4427.

Yu, J-Y., Wang, T-W., Parent, J.M., Vojtek, A.B., and Turner, D. L. (2005). Use of shRNA expression vectors for studying mammalian neural development. Methods in Enzymology 205: 186-199.