Aberrant neurodevelopment caused by GD3 synthase deficiency and its restoration of sea urchin ganglioside: insights from a CRISPR/Cas9-mediated st8sia1 knockout zebrafish

Ganglioside is a sialic acid-containing sphingolipid with multiple biological functions in neurodevelopment and neurodegeneration. The st8sia1-encoding GD3 synthase (GD3S) is involved in the biosynthesis of gangliosides GD3 and GD2, which are highly expressed in the developmental brain. However, the effects of exogenous gangliosides and endogenous glycosyltransferases GD3S on neurodevelopment remain to be determined due to the lack of in vivo ganglioside-deficient model. In this study, we generated st8sia1 knockout zebrafish using CRISPR/Cas9-mediated gene editing. A st8sia1 guide-RNA was designed to target exon 1 in zebrafish and generate the homozygote with a 13-bp frameshift deletion, which caused the loss of GD3S function and altered ganglioside profiles. The st8sia1 mutant showed delayed development, impaired locomotor behavior, and neurodevelopmental defects characterized by increased apoptosis of brain cells and small brain size. Further RNA-Seq analysis revealed that differentially expressed genes were enriched in axon and cellular development, neurogenesis, and neuroactive ligand-receptor interaction pathways. Notably, the application of exogenous GM4(1S) and GD3 could improve the phenotypes and behavioral activity of st8sia1 knockout zebrafish, as well as restore neurodevelopment with the underlying mechanism via upregulating the expressions of nestin, bdnf, map2, islet1, and elavl3. This study established a genetic model to elucidate the function of GD3S and exogenous ganglioside intervention in neurodevelopment. It provides the potential for high-throughput screening of bioactive molecules for brain health.