CERKL Knockdown Causes Retinal Degeneration in Zebrafish

Abstract

The human CERKL gene is responsible for common and severe forms of retinal dystrophies. Despite intense in vitro studies at the molecular and cellular level and in vivo analyses of the retina of murine knockout models, CERKL function remains unknown. In this study, we aimed to approach the developmental and functional features of cerkl in Danio rerio within an Evo-Devo framework. We show that gene expression increases from early developmental stages until the formation of the retina in the optic cup. Unlike the high mRNA-CERKL isoform multiplicity shown in mammals, the moderate transcriptional complexity in fish facilitates phenotypic studies derived from gene silencing. Moreover, of relevance to pathogenicity, teleost CERKL shares the two main human protein isoforms. Morpholino injection has been used to generate a cerkl knockdown zebrafish model. The morphant phenotype results in abnormal eye development with lamination defects, failure to develop photoreceptor outer segments, increased apoptosis of retinal cells and small eyes. Our data support that zebrafish Cerkl does not interfere with proliferation and neural differentiation during early developmental stages but is relevant for survival and protection of the retinal tissue. Overall, we propose that this zebrafish model is a powerful tool to unveil CERKL contribution to human retinal degeneration.

pVHL interacts with Ceramide kinase like (CERKL) protein and ubiquitinates it for oxygen dependent proteasomal degradation

“…If this holds true, pVHL may put selective pressure on these two duplicated genes, which leads to retain ceramide kinase activity in CERK and acquire antioxidant function in CERKL via gene neofunctionalization. Our present study strengthens the antioxidant (or stress response) function of CERKL [14,15,17,19], it also expands the functional spectrum of RP causative genes.…”

“…Besides control oxygen sensing via degrading HIFs [36], pVHL also involves in other processes [41][42][43][44]. On the other hand, CERKL mutations are responsible for retinitis pigmentosa, it encodes antioxidant protein to maintain photoreceptor survival [14,15,17,19]. Based on our results, we suggest pVHL may modulate photoreceptor survival by targeting CERKL for degradation.…”

“…By this, it enables CERKL to maintain photoreceptor's redox hemostasis timely. This idea is supported by CERKL is required for photoreceptor's daily survival but not its development [17]. Conversely, CERKL mutants which cannot activate TRX 2 will leave the uprising ROS untreated [15], which may induce photoreceptor apoptosis gradually by oxidative damage [4], the ROS induced ceramide [68], endoplasmic reticulum stress (ER stress) [4] and even inflammation [69].…”

“…3.2 Hypoxia regulates CERKL abundance at protein level CERKL acts as an antioxidant protein to maintain photoreceptor survival [14,15,17]. Thus, we hypothesize stress condition may up-regulate CERKL as it happens to A C C E P T E D M A N U S C R I P T…”

“…Additionally, CERKL is an mRNA binding protein and localizes in a cytoplasmic RNA-protein complex called stress granules (SGs), which increases in response to stress conditions [16]. CERKL is critical to photoreceptor survival but not development [17], its deficiency leads to retinal degeneration as a result of oxidative damage in both human [11,18] and animal models [15,17,19]. Although it is pivotal for photoreceptor survival, the regulatory mechanism of CERKL in response to stress remains unclear.…”