Analyses of the Spatiotemporal Expression and Subcellular Localization of Liprin-α Proteins

The members of the Liprin-alpha protein family, Liprin-alpha 1-4, are scaffolding proteins that play important roles in the regulation of synapse assembly and maturation, vesicular trafficking, and cell motility. Recent evidence suggests that despite their high degree of homology, the four isoforms can be differentially regulated and fulfill diverging functions. However, to date their precise regional and subcellular distribution has remained elusive. Here, we examine the spatiotemporal expression patterns of Liprins-alpha in the rodent by using in situ hybridization, immunoblotting, and immunochemistry of primary cells as well as brain and retina sections. We show that Liprin-alpha 1-4 mRNA and protein are widely expressed throughout the developing and adult central nervous system, with Liprin-alpha 2 and -alpha 3 being the major Liprin-alpha isoforms in the brain. Our data show that the four Liprin-alpha proteins differ in their regional distribution, in particular in the hippocampus, the cerebellum, and the olfactory bulb. Liprin-alpha 1 exhibits a unique spatiotemporal expression pattern as its levels decrease during synaptogenesis, and it is the only Liprin-alpha with substantial non-neuronal expression. Immunocytochemistry of cultured primary neurons with pre- and postsynaptic marker proteins shows all four Liprins-alpha to be present at synapses and nonsynaptic sites to varying degrees. Together, these results show that neurons in different brain regions express a distinct complement of Liprin-alpha proteins. J. Comp. Neurol. 519:3019-3039, 2011. (C) 2011 Wiley-Liss, Inc.