SUMMARY A central hypothesis for the limited capacity for adult central nervous system (CNS) axons to regenerate is the presence of myelin-derived axon growth inhibitors, the role of which, however, remains poorly understood. We have conducted a comprehensive genetic analysis of the three major myelin inhibitors, Nogo, MAG and OMgp, in injury-induced axonal growth, including compensatory sprouting of uninjured axons and regeneration of injured axons. While deleting any one inhibitor in mice enhanced sprouting of corticospinal or raphespinal serotonergic axons, there was neither associated behavioral improvement nor a synergistic effect of deleting all three inhibitors. Furthermore, triple mutant mice failed to exhibit enhanced regeneration of either axonal tract after spinal cord injury. Our data indicate that while Nogo, MAG and OMgp may modulate axon sprouting, they do not play a central role in CNS axon regeneration failure.

Background Stromal derived factor-1α (sdf-1α), a chemoattractant chemokine, plays a major role in tumor growth, angiogenesis, metastasis and in embryogenesis. The sdf-1α signaling pathway has also been shown to be important for somite rotation in zebrafish (Hollway, et al 2007). Given the known similarities and differences between zebrafish and Xenopus laevis somitogenesis, we sought to determine whether the role of sdf-1α is conserved in Xenopus laevis. Results Using a morpholino approach, we demonstrate that knockdown of sdf-1α or its receptor, cxcr4, leads to a significant disruption in somite rotation and myotome alignment. We further show that depletion of sdf-1α or cxcr4 leads to the near absence of β-dystroglycan and laminin expression at the intersomitic boundaries. Finally, knockdown of sdf-1α decreases the level of activated RhoA, a small GTPase known to regulate cell shape and movement. Conclusion Our results show that sdf-1α signaling regulates somite cell migration, rotation and myotome alignment by directly or indirectly regulating dystroglycan expression and RhoA activation. These findings support the conservation of sdf-1α signaling in vertebrate somite morphogenesis; however, the precise mechanism by which this signaling pathway influences somite morphogenesis is different between the fish and the frog.

Background: Stromal derived factor‐1α (sdf‐1α), a chemoattractant chemokine, plays a major role in tumor growth, angiogenesis, metastasis, and in embryogenesis. The sdf‐1α signaling pathway has also been shown to be important for somite rotation in zebrafish (Hollway et al., 2007). Given the known similarities and differences between zebrafish and Xenopus laevis somitogenesis, we sought to determine whether the role of sdf‐1α is conserved in Xenopus laevis. Results: Using a morpholino approach, we demonstrate that knockdown of sdf‐1α or its receptor, cxcr4, leads to a significant disruption in somite rotation and myotome alignment. We further show that depletion of sdf‐1α or cxcr4 leads to the near absence of β‐dystroglycan and laminin expression at the intersomitic boundaries. Finally, knockdown of sdf‐1α decreases the level of activated RhoA, a small GTPase known to regulate cell shape and movement. Conclusion: Our results show that sdf‐1α signaling regulates somite cell migration, rotation, and myotome alignment by directly or indirectly regulating dystroglycan expression and RhoA activation. These findings support the conservation of sdf‐1α signaling in vertebrate somite morphogenesis; however, the precise mechanism by which this signaling pathway influences somite morphogenesis is different between the fish and the frog. Developmental Dynamics 243:509–526, 2014. © 2013 Wiley Periodicals, Inc.

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