Cc2d2a is required for cilia axoneme development

Abstract

Purpose: Meckel syndrome is an embryonic lethal syndromic ciliopathy with pleiotropic clinical features like retinal dystrophy, mental retardation, polydactyly, liver fibrosis, and polycystic kidney. Meckel syndrome patients were reported to have mutations in CC2D2A (Coiled-Coil & C2 Domain containing 2A). CC2D2A protein was localized to the cilia basal body. The patient derived fibroblasts have basal body but they failed to develop cilia suggesting a mechanistic disconnect in the basal body due to CC2D2A mutation. To elucidate this mechanistic disconnect we have generated Cc2d2a loss of function diseases models in the zebrafish and mouse.

Methods: We used anti-sense splice blocking and translational blocking morpholinos (MOs) to knockdown the zebrafish cc2d2a. The splice blocking MO mimicked a disease-associated splicing defect in the patient. The Cc2d2a-knockout (Cc2d2a-/-) mouse was produced by targeted deletion of exons 6 to 8 relying on homologous recombination.

Results: The cc2d2a knockdown in the zebrafish embryos led to dose-dependent developmental defects in the brain and eye. The Cc2d2a-/- mouse exhibits embryonic lethality, with extensive developmental defects that include situs inversus, heterotaxy, polydactyly, anophthalmia, hydrocephalus and liver fibrosis. Occasionally, the Cc2d2a-/- mouse survived for a month but was with severe hydrocephalus and retinal dystrophy. Analysis of the embryonic node, embryonic fibroblasts, and kidney tubules showed that cilia biogenesis was disrupted in the Cc2d2a-/- mouse. Further analysis of the cilia markers revealed that gamma tubulin was normal but Arl13b was absent in Cc2d2a-/- fibroblasts.

Conclusions: Our studies suggest that Cc2d2a function is critical for normal body plan and organ development that involve cilia-mediated signaling pathways. We propose that Cc2d2a functioning at basal body is required for cilia axoneme development.

Keywords: 539 genetics • 696 retinal degenerations: hereditary • 695 retinal degenerations: cell biology