Leucine-rich repeat containing 8A contributes to the expansion of brain ventricles in zebrafish embryos

The sodium osmotic gradient is necessary for the initiation of brain ventricle inflation, but a previous study predicted that organic and inorganic osmolytes play equivalently important roles in osmotic homeostasis in astrocytes. To test whether organic osmoregulation also plays a role in brain ventricle inflation, the core component for volume-regulated anion and organic osmolyte channel, lrrc8a, was investigated in the zebrafish model. RT-PCR and whole-mount in situ hybridization indicated that both genes were ubiquitously expressed through to 12 hpf, and around the ventricular layer of neural tubes and the cardiogenic region at 24 hpf. Knocking down either one lrrc8a paralog with morpholino oligos resulted in abnormalities in circulation at 32 hpf. Morpholino oligos or CRISPR interference against either paralog led to smaller brain ventricles at 24 hpf. Either lrrc8aa or lrrc8ab mRNA rescued the phenotypic penetrance in both lrrc8aa and lrrc8ab morphants. Supplementation of taurine in the E3 medium and overexpression csad mRNA also rescued lrrc8aa and lrrc8ab morphants. Our results indicate that the two zebrafish lrrc8a paralogs are maternal message genes and are ubiquitously expressed in early embryos. The two genes play redundant roles in the expansion of brain ventricles and the circulatory system and taurine contributes to brain ventricle expansion via the volume-regulated anion and organic osmolyte channels.