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Complex processes following peripheral nerve injury integrate a number of various external cues and their intracellular responses resulting in the cytoskeletal remodeling. One of these cues, Slit protein, plays an important role in neuronal migration and axonal guidance through the interaction with Roundabout (Robo) receptor. It was reported that the signal from Robo is transmitted to a specific family of GTPase-activating proteins (GAPs) named Slit-Robo GAPs. The Slit-Robo GAPs (srGAPs) further transmit the signal to the actin cytoskeleton controlling Rho GTPases and thus provide a direct link between Slit-Robo signaling and actin cytoskeleton. We examined the effects of facial nerve transection on srGAP2 mRNA expression in the facial nerve nuclei by in situ hybridization. SrGAP2 mRNA was initially expressed, and its expression increased from 3 to 28 days after transection, with the peak at the seventh day after axotomy. The upregulation was found mostly in the neuronal cells and only to a small extent in the glial cells. Our results suggest that srGAP2, as a part of Slit-Robo pathway, plays an important role in the axonal regeneration after axotomy.

FERM domain including Rho GEF (FIR) is one of the guanine nucleotide exchange factors for Rac1. FIR, expressed in hippocampal and cortical neurons in vitro, is suggested to be involved in neurite remodeling. We examine developmental regulation of FIR mRNA expression in the mouse brain using in situ hybridization to get insight into its function. FIR mRNA is expressed in the ventricular zone and the intermediate zone as well as the cortical plate and the preplate in the brain from mice during the embryonic stages 12.5 to 14.5. In the brain during the later embryonic stages and the postnatal stages, the expression was restricted to the cortical plate. These results suggest that FIR may play a role not only in neurogenesis, but also in the asymmetrical cell division and migration of neurons.

FERM domain including Rho GEF (FIR) belongs to Dbl family of guanine nucleotide exchange factors and specifically activates biochemical pathways specific for Rac1. FIR was shown to regulate neurite remodeling of the embryonic neurons. Here we report a distribution of FIR mRNA in adult rat brain using in situ hybridization. The expression was found all throughout the brain with the most intensive signals in hippocampus, piriform cortex, red nucleus and nuclei of cranial nerves. The signal was predominantly localized in the neuronal cells.