Localization of CRMP5 mRNA by in situ hybridisation during development of the mouse forebrain.

The expression of the collapse response mediator protein CRMP5 in the prenatal mouse is largely unknown. Evidence suggests that CRMP family members play important roles in neurite outgrowth, and CRMP5 is known to modulate outgrowth of processes in oligodendrocytes through signalling via neuropilin-1 and SemaA. Furthermore, CRMP family members function in axon regeneration after injury and are implicated in the early stages of Alzheimer's disease. Despite these findings relatively little is known about the specific roles these proteins play. The aim of the present study was to evaluate CRMP5 expression in the developing mouse forebrain using in situ hybridisation. Serial coronal sections of brain from E12.5 to E18.5 were analysed. We found highly specific patterns of expression which were restricted to the post-mitotic layers of both the ganglionic eminence and neocortex, and an additional domain of strong expression in the pyramidal layers of the hippocampus in all prenatal ages. Our results are therefore consistent with a role for CRMP5 in process extension. Interestingly, our results also revealed a temporal switch in high-expression levels from the ganglionic eminence to the cortex at a critical time during tangential cell migration. However, the pattern of expression appeared more representative of a general permissiveness for neurite outgrowth rather than one which is restricted to a particular cell subset or cell class. Additionally, expression was also found during periods predominated by neurogenesis and not neurite extension. We conclude that expression of CRMP5 is consistent with a dynamic implicit role in forebrain development.