|
||||||
 |
Qiang Wu, Ph.D.
|
|||||
| Contribution to Society How billions of neurons in mammalian brain make trillions of precise connections is an intriguing problem. The Human Genomic Project has mapped the complete genetic code that determines these complex connections. By a combination of computational and experimental approaches, we have identified three closely-linked clusters of protocadherin (Pcdh) genes encoding more than fifty cell surface proteins that may play a role in neuronal connections. Our studies of these cell adhesion genes may provide insights into the normal brain development and abnormal brain tumor formation. Our research on the neural Pcdh genes may, in the long run, contribute to our understanding of many complex neurological diseases, such as schizophrenia and autism. Research Summary The main focus in our lab is to characterize three novel Pcdh gene clusters in brain development and function by using multidisciplinary approaches. We have identified more than fifty Pcdh genes that are expressed in the mammalian brain. These neural Pcdh genes could, in principle, provide the molecular basis for the complexity of cell-cell interactions in the brain. The genomic sequences of two of the three clusters have both "variable" and "constant" regions. The variable region of each cluster contains more than a dozen of large exons organized in a tandem array. Each variable region exon is separately spliced to the first constant region exon to generate diverse Pcdh mRNAs. The enormous diversity suggests that Pcdh proteins provide a synaptic adhesive code required for establishment and maintenance of complex networks of specific neuronal connections in the brain. We are investigating their roles in establishing and maintaining specific synaptic connections by a combination of genetics, genomics, biochemical and molecular approaches. For example, we have targeted several members of the mouse Pcdh cluster with reporters to study their expression patterns and to investigate their functions. These studies will contribute to our understanding of differential cell sorting during embryonic brain development and specific neuronal connection in the adult brain. We are also interested in DNA sequence analyses to identify patterns of genomic organizations in mammalian genomes. For example, we found that the genomic organization of the UDP clucuronosyltransferase (UGT1) cluster is strikingly similar to that of the Pcdh clusters. About a dozen highly similar UGT1 variable exons are organized in a tandem array. A common set of four UGT1 constant exons is located downstream from the variable exon tandem array. Each variable exon is separately spliced to the first constant exon to generate diverse UGT1 mRNAs encoding distinct protein isoforms. We also found that the I-branching acetylglucosaminyltransterase cluster has three highly similar variable exons each of which is separately spliced to a common set of downstream constant exons. Finally, we found several additional genes that have about a dozen variable first exons arranged in tandem and a common set of downstream constant exons; however, their variable exons do not display sequence similarity. We conclude that the variable and constant organization is more prevalent in the mammalian genome than previously thought, and provides a genomic framework for directing distinct cell- and tissue-specific patterns of gene expression. Recent Publications Wu, Q. (2005) Comparative genomics and diversifying selection of the clustered vertebrate protocadherin genes. Genetics, 169: 2179-2188. Zhang, T., Haws, P., and Wu, Q. (2004) Multiple variable first exons: a mechanism for cell- and tissue- specific gene regulation. Genome Research, 14: 79-89. Tasic, B., Nabholz, C. E., Baldwin, K. K., Kim, Y., Rueckert, E. H., Ribich, S. A., Cramer, P., Wu, Q., Axel, R., and Maniatis, T. (2002) Promoter choice determines splice site selection in protocadherin α and γ pre-mRNA splicing. Mol. Cell. 10:21-33. Wu, Q., Zhang, T., Cheng, J.-F., Kim, Y., Grimwood, J., Schmutz, J., Dickson, M., Noonan, J. P., Zhang, M. Q., Myers, R. M., and Maniatis, T. (2001) Comparative DNA sequence analysis of mouse and human protocadherin gene clusters. Genome Res. 11:389-404. Wu, Q., and Maniatis, T. (2000) Large exons encoding multiple ectodomains are a characteristic feature of protocadherin genes. Proc. Natl. Acad. Sci. USA 97:3124-3129. Pohl, U., Smith, J. S., Tachibana, I., Ueki, K., Lee, H. K., Ramaswamy, S., Wu, Q., Mohrenweiser, H. W., Jenkins, R. B., and Louis, D. N. (2000) EHD2, EHD3, and EHD4 encode novel members of a highly conserved family of EH domain-containing proteins. Genomics 63:255-262. Wu, Q., and Maniatis, T. (1999) A striking organization of a large family of human neural cadherin-like cell adhesion genes. Cell 97:779-790. Wu, Q., and Krainer, A. R. (1999) AT-AC pre-mRNA splicing mechanisms and conservation of minor introns in voltage-gated ion channel genes. Molecular and Cellular Biology 19:3225-3236. Wu, Q., and Krainer, A. R. (1998) Purine-rich enhancers function in the AT-AC splicing pathway and do so independently of intact U1 snRNP. RNA 4:1664-1673. Wu, Q., and Krainer, A. R. (1997) Splicing of a divergent subclass of AT-AC introns requires the major spliceosomal snRNAs. RNA 3:586-601. Wu, Q., and Krainer, A. R. (1996) U1-mediated exon definition interactions between
AT-AC and GT-AG introns. Science 274:1005-1008. |
|
