Tenascin N contributes to spinal motor nerve morphogenesis during development

Spinal motor nerves are an integral component of the nervous system whose development requires the coordination of many diverse cell types, including motor neurons, glia, and muscle. Although several molecular mechanisms guiding these interactions are known, many remain to be uncovered. Extracellular matrix (ECM) proteins also play a critical role in motor nerve assembly, yet their functions are less understood compared to classical pathfinding and guidance cues. Here, we identify a role for tenascin-n (tnn), an ECM glycoprotein, in spinal motor nerve development in zebrafish. Using in situ hybridization and immunohistochemistry, we show that tnn/Tnn is expressed and localized along vertical myosepta and the border of the ventral neural tube during spinal motor nerve development. To assess its function, we generated a CRISPR/Cas9 mutant allele, tnnuva96, and performed in vivo imaging and morphological analysis throughout motor nerve development. Loss of tnn leads to a subtle and transient trend of increase in ectopic motor axon exit and aberrant motor axon branching in the zebrafish trunk. Our findings reveal a previously unrecognized role for tnn in spinal motor nerve assembly and expand our understanding of the diverse molecular contributors to spinal motor nerve development and morphogenesis.