Crk adaptor proteins are necessary for the development of the zebrafish retina

The development of the nervous system requires intricate cell communication to tightly regulate important processes such as cellular migration, cell proliferation, and cell survival, to create the functional adult tissue. The CRK adaptor protein family is known to play an integral role in cell signaling needed for these developmental processes by clustering upstream and downstream signaling molecules to propagate cell communication. The CRK adaptor family consists of two proteins – CRK and CRK-like (or CRKL), and both are implicated in developmental diseases effecting the nervous system. Heterozygous compound deletion of human chromosome 17p13.3, which includes CRK, causes Miller-Dieker syndrome, characterized by lissencephaly (smooth brain), cardiac, renal, and craniofacial defects. Autosomal dominant compound deletion of human chromosome 22q11.2, including CRKL, is the cause of Di George syndrome, a neural crest migratory disease characterized by impaired cardiac development, craniofacial defects, and neurological developmental delay. Both molecules function in Reelin signaling to regulate neuronal migration responsible for patterning laminated tissues such as the cortex, cerebellum, and hippocampus, which could be a contributing factor in the human phenotypes. Due to the role of CRK and CRKL in neuronal migration, we aimed to determine if these proteins are important for development of another laminated central nervous system tissue, the retina. Using Danio rerio, or zebrafish, as a model system, we determined developmental gene expression profiles of crk and crkl and generated stable knockout lines of both genes using CRISPR/Cas9. Embryos lacking both Crk and Crkl have gross phenotypic abnormalities including heart edema, brain edema, and statistically smaller eye size when compared to control embryos. Transverse sections through the forebrain of these embryos reveals lamination defects within the retina, demonstrating that Crk and Crkl play a crucial role in patterning this tissue. Future research will focus on exploring potential cellular migration defects and cell signaling pathways these proteins might be mediating to drive retinal development