A Spontaneous Mutation in Rat Disrupts Early Development of the Lens Leading to Congenital Cataract and Microphthalmia

Abstract

Abstract: : Purpose: To describe the ocular phenotype, histopathology and the initial results from gene linkage analysis of a novel congenital cataract with microphthalmia(Nuc1) in the Sprague Dawley rat. Methods: Glycol methacrylate sections of embryonic and post-natal stages of wild-type, heterozygote, homozygote lenses were stained with standard hematoxylin and eosin for morphological analysis. Paraffin sections were used for staining nuclei using DAPI and for TUNEL staining for apoptotic cells. Homozygous cataract males (SD) were crossed to Wild-type Lewis females (Lew) and the resulting heterozygous (SD/Lew) F1 animals, all of which had the nuclear cataract phenotype were backcrossed to Wild-type Lewis rats. PCR-based Short Tandem Repeat Polymorphism genotype analysis is underway on the backcross progeny. We have also compared crystallins in lenses from Nuc1 and Wild-type rats by 2-D gel electrophoresis. Results:Heterozygotes exhibit dense nuclear opacity at birth, while all homozygotes have bilateral microphthalmia and severely disrupted lenses. As heterozygotes age, the morphological damage to the lens becomes progressively more severe, resulting in smaller lenses with ruptured posterior capsules. Repeated backcross matings to Wild-type Sprague Dawley rats are consistent with a single autosomal locus. DAPI staining shows retention of nuclei in fiber cells in heterozygotes; in homozygotes, nuclei are present throughout the disorganized lens material. Low levels of apoptosis in Nuc1 mutants are observed. Embryonic lenses(Nuc1/Nuc1 E16/E17)show retention of nuclei at the center of the lens and are smaller than wild-type controls. This is in stark contrast to the massive disruption of lens structure that is apparent in the Nuc1/Nuc1 animals four days later, at birth. 2D-gel data indicate that mutation of a crystallin gene is probably not the cause of Nuc1 and initial linkage data suggest no linkage to the region of chromosome 9 where some crystallins are localized. Conclusions:The Nuc1 mutant rat may be a particularly useful model system for studying the differentiation process during development of the lens, for probing molecular and cellular mechanisms involved in the maintenance of lens transparency and for analysis of organelle loss during maturation of fiber cells.

Keywords: animal model • cataract • genetics