High‐level expression of Dok‐1 in neurons of the primate prefrontal cortex and hippocampus

The docking protein p62Dok-1 (Dok-1) has a central role in cell signaling mediated by a wide range of protein tyrosine kinases, including intrinsic membrane kinases, such as the insulin-like growth factor-1 (IGF-1) receptor. To elucidate potential IGF signaling mechanisms, we used DNA array technology to investigate novel kinase targets expressed in the primate dorsolateral prefrontal cortex (DLPFC). Dok-1 transcripts were among the most abundant found in this structure. Because Dok-1 expression has not been characterized in brain, we evaluated its expression pattern using immunoblotting, in situ hybridization, and immunohistochemistry in the rhesus monkey prefrontal cortex and hippocampal formation. Dok-1 antibodies identified a 62-kDa band in lysates from the DLPFC, consistent with the known size for Dok-1. In situ hybridization showed that Dok-1 mRNA was expressed in all layers of the DLPFC and in all neuronal subregions of the hippocampal formation. Immunohistochemical analysis showed Dok-1 immunoreactivity concentrated in pyramidal neurons of cortical layers IV-V and throughout Ammon's horn and in granule neurons of the dentate gyrus. Dok-1 expression was also identified in endothelial cells of cerebral blood vessels. These expression patterns are very similar to those of the IGF-1 receptor and suggest that Dok-1 could be among the downstream targets of IGF signaling in areas of the primate brain involved in learning and memory.