SASH1 contributes to glial cell migration in the early development of the central nervous system

SAM and SH3 domain-containing 1 (SASH1), a member of the SLy protein family, is a tumor suppressor gene that has been studied for its association with various cancers. SASH1 is highly expressed in the mammalian central nervous system, particularly in glial cells, and is expressed in the central nervous system during zebrafish embryo development. However, SASH1's role in brain development has rarely been investigated. In this study, Morpholino oligonucleotides (MO) were used to down-regulate sash1a expression in zebrafish to observe morphological changes in the brain. Three transgenic zebrafish lines, Tg(gfap:eGFP), Tg(hb9:eGFP), and Tg(coro1a:eGFP) were selected to observe changes in glial cells, neurons, and immune cells after sash1a knockdown. Our results showed that the number of microglia residing in the developmental brain was reduced, whereas the axonal growth of caudal primary motor neurons was unaffected by sash1a downregulation. And more significantly, the gfap ⁺ glia presented abnormal arrangements and disordered orientations in sash1a morphants. The similar phenotype was verified in the mutation induced by the injection of cas9 mRNA and sash1a sgRNA. We further performed behavioral experiments in zebrafish larvae that had been injected with sash1a MO at one-cell stage, and found them exhibiting abnormal behavior trajectories. Moreover, injecting the human SASH1 mRNA rescued these phenomena in sash1a MO zebrafish. In summary, our study revealed that the downregulation of SASH1 leads to malformations in the embryonic brain and disorganization of glial cell marshalling, suggesting that SASH1 plays an important role in the migration of glial cells during embryonic brain development.