Myelination of critical nerves in the peripheral nervous system is critical for proper nerve function, and the process of selecting and ensheathing specific nerves is performed by Schwann cells (SCs) in a process known as radial sorting. Defective radial sorting leads to peripheral neuropathies; thus, significant investigation towards understanding regulatory mechanisms of this process are ongoing. Small GTPases like Rac1 have been shown to regulate radial sorting through NF2, but studies using dominant-negative NF2 in Rac1 mutant mice suggested that this small GTPase regulates radial sorting through additional mechanisms. Weaver et. al. sought to identify additional Rac1 dependent mechanisms and linked Rac1-STRN3 regulation of the Hippo pathway, a kinase signaling pathway that culminates in the activation in YAP and TAZ transcriptional activators, as a driver of laminin receptor expression to control radial sorting in SCs. Active and inactive Rac1 pull-down screening studies were performed using peripheral nerve lysate. Interestingly, key proteins of the STRIPAK complex, STRN3 and MOB4, were shown to bind GTP-bound Rac1, which were confirmed via Co-IP and proximity ligation assay (PLA) studies. To confirm that these interactions were direct, dot blot assays using purified GTP- or GDP-Rac1 were performed, and the results showed that both MOB4 and STRN3 directly bind active Rac1 preferentially. They then showed that loss of STRN3 had similar effects to Rac1 depletion in SCs, such as suppressed lamellipodia formation, defective cell elongation, and defective radial sorting. Some of the more pronounced effects like defective radial sorting required depletion of both STRN3 and STRN1, suggesting potential compensatory effects. Ultimately, the group showed that the Rac1 and STRN3 complex regulates SC laminin recepter expression via YAP and TAZ transcriptional regulation. Cytoskeleton Inc.’s Rac1 product such as our His-Rac1 protein (Cat. # RC01), anti-Rac1 antibody (Cat. # ARC03), and purified PAK-PBD (Cat. # PAK01) were critical tools utilized throughout the study and specifically in the in vitro dot blot studies characterize the interaction between Rac1 and STRIPAK proteins.
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Products Used in Citation:
Rac1 protein: His tagged: human wild type (Cat # RC01) Anti-Rac1: mouse Mab (Cat # ARC03) PAK-PBD protein, GST-tagged (Cat # PAK01)
