Abstract

CRISPR-Cas is a novel tool that may pinpoint the underlying cause of eye diseases. Here, we introduce the different types of CRISPR-Cas systems with an emphasis on type II and present its applications in eye diseases based on previous reports. The CRISPR microbiome is perhaps bigger than the universe. Bacteria contain a self-defense adaptive immune system known as CRISPR (clustered regularly interspaced short palindromic repeats)-Cas (CRISPR-associated genes) which inactivates invading phages, plasmids, or foreign DNA sequences. CRISPR is an array of repeats separated by spacers along with cas genes. In bacteria CRISPR-array and cas genes together form a cascade complex to destroy the invading foreign DNA. The two important components, the Cas9 nuclease, and the short guide RNA are introduced for a targeted genetic event. The short guide-RNA is the fingerprint of the target DNA. CRISPR-Cas has been successfully demonstrated in RHO, CRYAA, tyr, gol, ddx19, and mitfa genes in zebrafish, mice, and rabbits. The nuclear homeoprotein Six3 mutations by CRISPR-Cas showed eye and anterior head defects in zebrafish. Moreover, CRISPR-Cas has been successfully shown in Crygc gene repair in the cataract mice model carrying 1bp deletion in exon3 of Crygc. The transcription factors like Rx, Six3, Pax6, Sox2, and signaling factors involved in eye formation can be further studied by CRISPR-Cas. The first patient ever to receive CRISPR-Cas9 construct for fixing mutations in a centrosomal protein of 290 kDa, CEP290, is for the blindness caused by a rare disorder in the retina, Leber’s congenital amaurosis 10 (LCA10). It is injected directly into the eye near photoreceptor cells and is a landmark clinical trial. The present CRISPRCas technology opens a new perspective for new treatments of cataract, retinitis pigmentosa, refractive index error, and any other eye diseases.

Keywords: CRISPR-Cas, CRISPR-array, Cas9 endonuclease, crRNA, sgRNA, Protospacer, PAM