CRISPR-derived mouse model of North Carolina Macular Dystrophy reveals in trans tissue-specific upregulation of PRDM13

Abstract

Purpose : For fuller understanding of the disease mechanisms in North Carolina Macular Dystrophy (NCMD), we set out (i) to create a mouse model carrying the duplication of the non-coding region on chromosome 5p (linked to MCDR3); (ii) to identify further causative variants in unsolved cases of macular dystrophies (MD).

Methods : (i) CRISVar (CRISPR/Cas-induced structural variants) technology was used to reproduce the duplication of a non-coding region between IRX1 and ADAMTS16 (chr5) recurrently identified in NCMD families. Selective gene expression analysis was performed on the developing eye and limb-bud, two tissues expressing the flanking genes, from mutant and control mice. Chromosome conformation capture (c-HI-C) and chromatin immunoprecipitation (ChIP-seq) were also carried out on the same tissues to map architectural folding of chromatin and histone marks decorating regulatory elements.
(ii) Unsolved families with congenital MD were subjected to genomic sequence studies including whole genome sequencing.

Results : (i) Expression of PRDM13 was substantially elevated in eye but not limb-bud tissue in the mouse model versus control. c-Hi-C at the MCDR3 locus showed unique chromatin interactions in developing wild-type eye versus limb-bud, suggesting distinct tissue-specific use of regulatory regions.
(ii)The canonical 43kb duplication, identified as an ancestral allele in 9 of 10 published duplication cases of NCMD, was also observed in two further cases: in the MCDR4 family, with NCMD plus hearing loss, and in one of the recently described Benign Yellow dot Maculopathy families. 9 MD families remain unsolved.

Conclusions : The observed eye-specific over-expression of PRDM13, a previously suggested candidate gene for NCMD located in 6q, provides the first molecular evidence that elevated PRDM13 expression may be the main cause of the NCMD phenotype. It also represents the first molecular evidence to link the two loci biologically. The mechanism of interaction between the MCDR3-putative element and downstream PRDM13 expression control remains to be elucidated. Further molecular phenotyping of the created mouse model may advance our knowledge. The chromatin organization studies highlight the importance of tissue specific DNA contacts in development and disease. Exploration of the unsolved cases may uncover additional molecular targets for NCMD.

This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.