A knock- in mouse model for recessive RP-foveoschisis-optic disc drusen and nanophthamos syndrome due to a mutation in the Mfrp gene

Abstract

Purpose: To characterize the phenotype of a mouse model for retinitis pigmentosa(RP)-foveoschisis-optic disc drusen and nanonophthalmos syndrome due to a single base pair insertion (c498_499insC) in exon 5 of Membrane-type frizzled related protein (MFRP) gene.

Methods: The Mfrp homozygous c498_499insC mutation knock-in (KI) mice were generated on a C57BL/6 background. The ocular phenotype was characterized by fundus imaging, optical coherence tomography (OCT), fundus autofluorescence and measuring axial length. Retinal morphology was evaluated by microscopy. Expression of selected marker genes was measured by RT-PCR and marker proteins were studied by immunohistochemistry and western blot analysis.

Results: The Mfrp c498_499InsC mutation KI mice developed RPE atrophy with, progressive loss of photoreceptors beginning before post-natal day 21. Both retinal histology and OCT revealed a significant decrease in the thickness of the retina by 1 month. The outer nuclear layer (ONL) has about 8 rows of nuclei at 21 days, 2 to 3 rows at two months and just a single row of nuclei by 12 months. Presence of hyperautofluorescent spots throughout the retina was observed starting at age one month. The focal length to the retinal nerve fiber layer (RNFL), a surrogate measure for the axial length of the eye, showed the eyes of Mfrp homozygous KI mice to be significantly smaller compared to age matched wild-type mice (P<0.0001). Expression of Mfrp was noted to be significantly depleted.

Conclusions: Mice carrying the Mfrp c498_499InsC mutation in the homozygous state developed retinal degeneration and microphthalmos mimicking the human phenotype in patients with the same MFRP mutation.

Keywords: 696 retinal degenerations: hereditary • 539 genetics • 695 retinal degenerations: cell biology