Knockdown of a galectin-1-like protein in zebrafish (Danio rerio) causes defects in skeletal muscle development

We previously identified and characterized four galectin-1-like proteins in zebrafish, Drgal1-L1, Drgal1-L2, Drgal1-L3, and one splice variant of Drgal1-L2, of distinct ontogenic expression. Drgal1-L1 is maternal; Drgal1-L2 is zygotic and strongly expressed in the notochord, while Drgal1-L3 is both maternal and zygotic. Knockdown experiments in zebrafish embryos using a morpholino-modified antisense oligo targeted to the 5'-UTR sequence of Drgal1-L2 resulted in a phenotype with a bent tail and disorganized muscle fibers. This effect was dose-dependent as follows: 62-66% at 17 ng, 29-35% at 5.7 ng, 21-28% at 1.9 ng, and 14-17% at 0.6 ng. However, no (or a negligible number of) Drgal1-L1 knockdown embryos showed similar morphological defects, indicating that the observed effects are sequence-specific, and not due to the toxicity of the morpholino-modified oligos. Further, ectopic expression of native Drgal1-L2 specifically rescued the phenotype, as co-injection of the full-length sense Drgal1-L2 mRNA with Drgal1-L2-MO yielded 60-62% normal embryos. As the notochord serves as the primary source of signaling molecules required for proper patterning of adjacent tissues, such as neural tube, somites, and heart, these results suggest that galectins produced by the notochord play a key role in somitic cell differentiation and development.