Characterization of the Shank family of synaptic proteins - Multiple genes, alternative splicing, and differential expression in brain and development

Shank1, Shank2, and Shank3 constitute a family of proteins that may functio n as molecular scaffolds in the postsynaptic density (PSD). Shank directly interacts with GKAP and Homer, thus potentially bridging the N-methyl-D-asp artate receptor-PSD-95-GKAP complex and the mGluR-Homer complex in synapses (Naisbitt, S., Kim, E., Tu, J. C., Xiao, B., Sala, S., Valtschanoff, J., W einberg, R J., morley, P. F., and Sheng, M. (1999) Neuron 23, 569-582; Tu, J. C., Xiao, B., Naisbitt, S., Yuan, J. P., Petralia, R. S., Brakeman, P., Dean, A., Aakalu, V. K., Lanahan, A. A., Sheng, M., and Worley, P. F. (1999 ) Neuron 23, 583-592). Shank contains multiple domains for protein-protein interaction including ankyrin repeats, an SH3 domain, a PSD-95/DIg/ZO-1 dom ain, a sterile a motif domain, and a proline-rich region. By characterizing Shank cDNA clones and RT-PCR products, we found that there are four sites far alternative splicing in Shank1 and another four sites in Shank2, some o f which result in deletion of specific domains of the Shank protein. In add ition, the expression of the splice variants is differentially regulated in different regions of rat brain during development. Immunoblot analysis of Shank proteins in rat brain using five different Shank antibodies reveals m arked heterogeneity in size (120-240 kDa) and differential. spatiotemporal expression. Shank1 immunoreactivity is concentrated at excitatory synaptic sites in adult brain, and the punctate staining of Shank1 is seen in develo ping rat brains as early as postnatal day 7. These results suggest that alt ernative splicing in the Shank family may be a mechanism that regulates the molecular structure of Shank and the spectrum of Shank-interacting protein s in the PSDs of adult and developing brain.