Drosophila models of SNRNP200-retinitis pigmentosa exhibit retinal apoptosis and loss of photoreceptor function
Authors: Sara Mayer; Quinton Christensen; Arlene Drack; Lori Wallrath
Affiliation: University of Iowa
Keywords: x. other (Retinal degeneration); q. vision
Retinitis pigmentosa (RP) represents a collection of genetic eye disorders that cause gradual loss of photoreceptors. The initial phases of RP involve loss of rod photoreceptor function, which leads to loss of cone photoreceptor function and eventual blindness. RP affects 1:4,000 people worldwide and is either syndromic or non-syndromic. RP33 is a non-syndromic form of RP caused by mutations in the SNRNP200 gene, which encodes a core component of the spliceosome. SNRNP200 possesses helicase activity that plays a critical role in pre-mRNA splicing. SNRNP200 is expressed in nearly every cell type, yet defects are only observed in the retina. To understand the function of SNRNP200 in vision, we turned to Drosophila. The Drosophila orthologue of human SNRNP200 is lethal(3)72Ab (or Brr2), which we refer to as dSNRNP200. Human SNRNP200 and fly dSNRNP200 have 74% amino acid identity and 89% similarity. Null mutations in dSNRNP200 are homozygous lethal. RNAi knock-down of dSNRNP200 in the developing eye leads to increased apoptosis in the larval eye/antennal imaginal discs and an adult rough eye phenotype. To understand human disease mechanisms, we generated patient based CRISPR mutant alleles encoding single amino acid substitutions in the first helicase domain. The CRISPR alleles showed no obvious physical defects; however, upon investigation they had increased apoptosis in larval eye/antennal imaginal discs relative to controls. Furthermore, electroretinograms performed on young adults bearing the CRISPR mutant alleles exhibited abnormal waveforms indicative of loss of phototransduction and synaptic transmission that progressed with age, similar to the human disease condition. In addition, loss of prolonged action potential indicated that the “rod-like” cells of the retina, were defective. By contrast, the cone-like cells, appeared functional, recapitulating early stages of the human disease. Collectively, we found that globally expressed dSNRNP200 is essential for Drosophila photoreceptor function and modeling RP33 mutations in the fly recapitulates many aspects of the human disease, allowing for a molecular genetic dissection of disease mechanisms.