The abcc6a gene expression is required for normal zebrafish development

Pseudoxanthoma elasticum (PXE) is caused by mutations in the ABCC6 gene, which encodes a putative efflux transporter, ABCC6. The zebrafish (Danio rerio) has two ABCC6-related sequences. To study the function of abcc6 during zebrafish development, the mRNA expression levels were measured using RT-PCR and in situ hybridization. The abcc6a showed a relatively high level of expression at 5 days post-fertilization (d.p.f.) and the expression was specific to the Kupffer's vesicles. The abcc6b expression was evident at 6 hours post-fertilization (h.p.f.) and remained high up to 8 d.p.f., corresponding to embryonic kidney proximal tubules. Morpholinos were designed to both genes to prevent pre-mRNA splicing and block translation. Injection of the abcc6a morpholinos into 1-4 cell zebrafish embryos decreased gene expression by 54-81%, and induced a phenotype, pericardial edema and curled tail associated with death at around 8 d.p.f. Microinjecting zebrafish embryos with full-length mouse Abcc6 mRNA together with the morpholino completely rescued this phenotype. No phenotypic changes were observed when the abcc6b gene morpholino was injected into embryos with knock-down efficiency of 100%. These results suggest that abcc6a is an essential gene for normal zebrafish development and provide insight into the function of ABCC6, the gene mutated in PXE.