Epistasis between Pax6Sey and genetic background reinforces the value of defined hybrid mouse models for therapeutic trials

Jack W Hickmott,Kimberly Jensen,Andrea J Korecki,Elizabeth M Simpson,Uvini Gunawardane

doi:10.1038/s41434-018-0043-6

Jack W Hickmott, Kimberly Jensen + Show 3 more

Open Access

https://doi.org/10.1038/s41434-018-0043-6

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Abstract

The small eye (Sey) mouse is a model of PAX6-aniridia syndrome (aniridia). Aniridia, a congenital ocular disorder caused by heterozygous loss-of-function mutations in PAX6, needs new vision saving therapies. However, high phenotypic variability in Sey mice makes development of such therapies challenging. We hypothesize that genetic background is a major source of undesirable variability in Sey mice. Here we performed a systematic quantitative examination of anatomical, histological, and molecular phenotypes on the inbred C57BL/6J, hybrid B6129F1, and inbred 129S1/SvImJ backgrounds. The Sey allele significantly reduced eye weight, corneal thickness, PAX6 mRNA and protein levels, and elevated blood glucose levels. Surprisingly, Pax6Sey/Sey brains had significantly elevated Pax6 transcripts compared to Pax6+/+ embryos. Genetic background significantly influenced 12/24 measurements, with inbred strains introducing severe ocular and blood sugar phenotypes not observed in hybrid mice. Additionally, significant interactions (epistasis) between Pax6 genotype and genetic background were detected in measurements of eye weight, cornea epithelial thickness and cell count, retinal mRNA levels, and blood glucose levels. The number of epistatic interactions was reduced in hybrid mice. In conclusion, severe phenotypes in the unnatural inbred strains reinforce the value of more naturalistic F1 hybrid mice for the development of therapies for aniridia and other disorders.

Highlights

In humans, aniridia is a penetrant monogenic disorder with high phenotypic variability, even between family members with the same mutation [1]
Exclusively in bkgds: C57BL/6J (B6) mice, a subset of Het mice presented with severe microphthalmia, where the eye was so small that it resembled anophthalmia, as no eye was externally visible, and the eyelids were closed
Two-way analysis of variance (ANOVA) confirmed that Pax6 genotype and bkgd (p < 0.001 for both) both influenced eye weight, where B6 eyes were found to be significantly lighter than F1 and 129 eyes (p < 0.001 for both) (Fig. 1b and Fig. S1)

Summary

Introduction

Aniridia is a penetrant monogenic disorder with high phenotypic variability, even between family members with the same mutation [1]. The result of PAX6 haploinsufficiency, aniridia is a rare genetic disorder predominantly affecting the eyes, central nervous system, and pancreas [3,4,5,6,7,8,9,10,11,12,13]. In addition to congenital fovea hypoplasia and lens abnormalities that often reduce vision from birth, cataracts, glaucoma, corneal keratopathy, and pannus can progressively obscure vision. The consequence of such progressive visual impairments is often blindness in young adulthood [14, 15], necessitating the development of new vision saving therapies. While environmental factors are likely to contribute to the reported variability, epistasis, the non-additive interaction between genetic loci, may be a factor influencing how the disorder presents, and how it should be treated [16, 17]

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