Genetic compensation highlights the importance of neural cell adhesion molecule Ncam1 paralogs in balancing signaling pathways during zebrafish lateral line development

The neural cell adhesion molecule NCAM1 is essential for neuronal development and enables organized cell migration, axon growth, and fasciculation. As a result of genome duplication in zebrafish, the paralogs Ncam1a and Ncam1b arose. Our previously published findings using morpholino knockdown experiments demonstrated the essential role of Ncam1b in the development of the zebrafish lateral line system, a mechanosensory organ critical for detecting water movements. ncam1b morphants exhibited severe defects, including impaired primordium migration, disrupted proneuromast deposition, and reduced cell proliferation within the primordium. These defects were linked to a disrupted interaction between Ncam1b and Fgfr1a, which led to compromised proliferation and abnormal lateral line development. The current study reveals that ncam1b mutants, however, unlike morphants, do not show this severe phenotype. Instead, we observed subtle alterations, including altered FGF and Wnt signaling and a redistribution of proliferating cells within the primordium. Notably, ncam1b mutants displayed elevated levels of the paralog ncam1a mRNA. The knockdown of either ncam1a or upf3a in ncam1b mutants resulted in a phenotype resembling that of ncam1b morphants. Upf3a is a key regulator of genetic compensation, a well-known phenomenon in zebrafish research. This supports the hypothesis that upregulated ncam1a compensates for the loss of ncam1b, facilitating normal lateral line development. These findings emphasize the essential role of Ncam1 in zebrafish lateral line development and suggest that the retention of both paralogs, ncam1a and ncam1b, acts as a protective mechanism to ensure the preservation of critical Ncam1 functions after gene duplication.