Molecular cloning and dendritic localization of rat SH3P7

SH3P7 was originally isolated by cloning SH3 domain ligand targets from a m ouse embryo cDNA library. SH3P7 is an actin-binding protein implicated in a ntigen reception, JNK1 signalling, and Rao activation. It contains a drebri n homology sequence in its N-terminal region and a cortactin homology seque nce (SH3 domain) in its C-terminal region. Both drebrin and cortactin,are a ctin-binding proteins, and both have been suggested as possible regulators of the actin cytoskeleton in neurons. In the present study, we performed cD NA cloning of rat SH3P7, performed RT-PCR analysis, generated polyclonal an tibodies against the recombinant rat SH3P7 protein, and examined the distri bution of SH3P7 in the rat brain using immunohistochemistry. Sequence analy sis revealed that there were at least four isoforms of the SH3P7 protein: S H3P7r1-SH3P7r4. RT-PCR analysis revealed that the predominant isoforms expr essed in the brain were SH3P7r1 and SH3P7r3. The relative levels of isoform expression were similar among regions. Immunohistochemistry revealed that the most intense immunolabelling for SH3P7 was observed in. the hippocampus and cerebellar cortex. Double-labelling studies with anti-SH3P7 antibody a nd other neuronal market proteins revealed that SH3P7 was located primarily in dendrites, and in moderate amounts in cell bodies. Immunoreactivity was absent in the presynaptic terminals. In cultured astrocytes, SH3P7 was loc alized at protrusive structures of the cell periphery and in the cell body. We concluded. that SH3P7 is ubiquitous in the rat brain, and occurs as sev eral isoforms. Also, its dendritic localization suggests that SH3P7 is func tionally linked to actin cytoskeleton organization in dendrites.