s-ccdc80 is involved in axon guidance of zebrafish primary motoneurons

The similar to ccdc80 (s-ccdc80) gene was in silico identified on the basis of its high nuclear sequence identity (56,6%) with zebrafish ccdc80 (coiled-coil domain containing 80). The analysis of s-ccdc80 temporal/spatial expression by means of RT-PCR and whole mount in situ hybridization revealed its diffuse expression at early developmental stages and in epiboly. During somitogenesis up to 48 hours post fertilization, s-ccdc80 is expressed in specific territories such as cranial ganglia, ventral portion of somites, migrating adaxial cells and muscle pioneers, dorsal dermis and caudal vein plexus region. s-ccdc80 knock-down through the injection of a specific morpholino did not lead to morphological body plan defects nor alteration of the expression of several myogenic markers, though motility resulted affected. Thus, we decided to investigate the motoneuronal development in knocked-down embryos, also bearing in mind s-ccdc80 expression in territories involved in motoneurons patterning and axonal pathfinding: muscle pioneers and adaxial cells. s-ccdc80 knock-down led to axonal outgrowth defects of two primary motoneurons (CaP and Mip), that branched excessively and followed aberrant pathways. Our results strongly suggest that s-ccdc80 is involved in the guidance of the axonal extension of primary motoneurons but not in their proper formation. Furthermore, s-ccdc80 expression seemed to be positively regulated by the Hedgehog pathway.