Investigating the Role of Zebrafish Retinoschisin Homologs Rs1a and Rs1b During Retinal Development

Deficiency in the retinoschisin protein (RS1) causes X-linked juvenile retinoschisis (XLRS), a retinal degenerative disease that disrupts retinal layers and forms cystic cavities. In addition to its structural function, RS1 is believed to play a role in retinal development. A zebrafish model may provide insights into the role of Rs1 in the earliest stages of retinal development. To explore this, we created a zebrafish model with RS1 deficiency by knocking down the two homologs, Rs1a and Rs1b. Gene expression and protein presence were assessed in Wildtype Tüpfel Longfin zebrafish at 1, 24, 48, 72, 96, and 120 h post-fertilization (hpf). We then performed morpholino (MO)-mediated knockdown targeting rs1a and rs1b mRNA, using scrambled oligos (SC) as controls. MOs or SCs were injected at the 1-4 cell stage, and samples were collected at 48, 72, 96, and 120 h post-fertilization (hpf). The effects were analyzed using immunohistochemistry (IHC) and RNA sequencing. Expression of rs1a and rs1b was first observed at 48 hpf. The successful knockdown of Rs1 was confirmed via IHC. At 72 hpf, Rs1 protein presence was eliminated without affecting overall embryo development. Transcriptional analysis showed enrichment of genes related to axon guidance at 72 hpf and visual perception at 96 hpf. On IHC, photoreceptor protein levels were lower in MO-injected retinae at 96 and 120 hpf. Our findings align with those observed in rodent and organoid models for XLRS, demonstrate the potential of the zebrafish model for XLRS, and advocate for continued research on Rs1 in zebrafish.