Nephronophthisis-related ciliopathies (NPHP-RC) are recessive disorders featuring dysplasia or degeneration preferentially in kidney, retina, and cerebellum. Here we combine homozygosity mapping with candidate gene analysis by performing “ciliopathy candidate exome capture” followed by massively-parallel sequencing. We detect 12 different truncating mutations of SDCCAG8 in 10 NPHP-RC families. We demonstrate that SDCCAG8 is localized at both centrioles and directly interacts with NPHP-RC-associated OFD1. Depletion of sdccag8 causes kidney cysts and a body axis defect in zebrafish and induces cell polarity defects in 3D renal cell cultures. This work identifies SDCCAG8 loss of function as a novel cause of a retinal-renal ciliopathy and validates exome capture analysis for broadly heterogeneous single-gene disorders.

Malignant melanomas often harbor activating mutations in BRAF (V600E) or, less frequently, in NRAS (Q61R). Intriguingly, the same mutations have been detected at higher incidences in benign nevi, which are largely composed of senescent melanocytes. Overexpression of BRAFV600E or NRASQ61R in human melanocytes in vitro has been shown to induce senescence, although via different mechanisms. How oncogene-induced senescence is overcome during melanoma progression remains unclear. Here, we report that in the majority of analysed BRAFV600E- or NRASQ61R-expressing melanoma cells, C-MYC depletion induced different yet overlapping sets of senescence phenotypes that are characteristic of normal melanocytes undergoing senescence due to overexpression of BRAFV600E or NRASQ61R, respectively. These senescence phenotypes were p16INK4A- or p53-independent, however, several of them were suppressed by genetic or pharmacological inhibition of BRAFV600E or phosphoino-sitide 3-kinase pathways, including rapamycin-mediated inhibition of mTOR-raptor in NRASQ61R-expressing melanoma cells. Reciprocally, overexpression of C-MYC in normal melanocytes suppressed BRAFV600E-induced senescence more efficiently than NRASQ61R-induced senescence, which agrees with the generally higher rates of activating mutations in BRAF than NRAS gene in human cutaneous melanomas. Our data suggest that one of the major functions of C-MYC overexpression in melanoma progression is to continuous suppress BRAFV600E- or NRASQ61R-dependent senescence programs.

Primary cilia regulate polarized protein trafficking in photoreceptors, which are dynamic and highly compartmentalized sensory neurons of retina. The ciliary protein Cep290 modulates cilia formation and is frequently mutated in syndromic and non-syndromic photoreceptor degeneration. However, the underlying mechanism of associated retinopathy is unclear. Using the Cep290 mutant mouse rd16 (retinal degeneration 16), we show that Cep290-mediated photoreceptor degeneration is associated with aberrant accumulation of its novel interacting partner Rkip (Raf-1 kinase inhibitory protein). This effect is phenocopied by morpholino-mediated depletion of cep290 in zebrafish. We further demonstrate that ectopic accumulation of Rkip leads to defective cilia formation in zebrafish and cultured cells, an effect mediated by its interaction with the ciliary GTPase Rab8A. Our data suggest that Rkip prevents cilia formation and is associated with Cep290-mediated photoreceptor degeneration. Furthermore, our results indicate that preventing accumulation of Rkip could potentially ameliorate such degeneration.