Integrins Have Cell-Type-Specific Roles in the Development of Motor Neuron Connectivity

Axon development is regulated at genetic and proteomic interfaces between the integrin adhesome and the RPM-1 ubiquitin ligase signaling hub

Integrin signaling plays important roles in development and disease. An adhesion signaling network called the integrin adhesome has been principally defined using bioinformatics and proteomics. To date, the adhesome has not been studied using integrated proteomic and genetic approaches. Here, proteomic studies in C. elegans identified physical associations between the RPM-1 ubiquitin ligase signaling hub and numerous adhesome components including Talin, Kindlin and beta-integrin. C. elegans RPM-1 is orthologous to human MYCBP2, a prominent player in nervous system development associated with a neurodevelopmental disorder. Using neuron-specific, CRISPR loss-of-function strategies, we show that core adhesome components affect axon development and interact genetically with RPM-1. Mechanistically, Talin opposes RPM-1 in a functional 'tug-of-war' on growth cones that is required for accurate axon termination. Thus, our findings orthogonally validate the adhesome via multi-component genetic and physical interfaces with a key neuronal signaling hub and identify new links between the adhesome and brain disorders.

Characterizing the diverse cells that associate with the developing commissures of the zebrafish forebrain

During embryonic development of bilaterally symmetrical organisms, neurons send axons across the midline at specific points to connect the two halves of the nervous system with a commissure. Little is known about the cells at the midline that facilitate this tightly regulated process. We exploit the conserved process of vertebrate embryonic development in the zebrafish model system to elucidate the identity of cells at the midline that may facilitate postoptic (POC) and anterior commissure (AC) development. We have discovered that three different gfap+ astroglial cell morphologies persist in contact with pathfinding axons throughout commissure formation. Similarly, olig2+ progenitor cells occupy delineated portions of the postoptic and anterior commissures where they act as multipotent, neural progenitors. Moreover, we conclude that both gfap+ and olig2+ progenitor cells give rise to neuronal populations in both the telencephalon and diencephalon; however, these varied cell populations showed significant developmental timing differences between the telencephalon and diencephalon. Lastly, we also showed that fli1a+ mesenchymal cells migrate along the presumptive commissure regions before and during midline axon crossing. Furthermore, following commissure maturation, specific blood vessels formed at the midline of the POC and immediately ventral and parallel to the AC. This comprehensive account of the cellular populations that correlate with the timing and position of commissural axon pathfinding has supported the conceptual modeling and identification of the early forebrain architecture that may be necessary for proper commissure development.