Novel Cataractous Mouse Mutants

Abstract

Abstract: : Purpose: To identify cataractous mouse mutants from an ENU induced mouse mutagenesis program in C57BL/6J strain and to characterize the mouse mutations that develop different types of cataracts. Methods: A slit-lamp and an indirect ophthalmoscope were used to examine for lens phenotypes in mice. Identified mutants were crossed with C3H mice for mapping the chromosome location of the mutant allele. Mutant mice were characterized morphologically and biochemically for their lens phenotypes at different developmental stages. Results: Several mutants have been identified from the screening of the ENU induced mutagenesis mice. They developed different types of cataracts : nuclear cataract and posterior polar cataract etc. The first identified mutant, BEML1, is a semi-dominant mutation. These mice developed microphthalmia with nuclear cataracts. Histological data showed vacuoles, and /or enlarged intercellular spaces between lens epithelium and fibers. Some of the mutants also developed posterior ruptured lens. No obvious changes of alpha, beta-, and gamma- crystallins in the mutant lens. However, a decreased level of phosphorylated forms of alpha3 connexin were detected in the homogenates of the mice with severe cataracts by western blotting. Primary mapping data suggested the mutation was likely to be located in chromosome 3. We are in the process to identify whether it is a novel mutation of alpha8 connexin ( Gja8) since Gja8 is not only located in chromosome 3 but also one of the hottest allele for the ENU-induced mutations. However, additional analysis of more mutant mice will be necessary to determine a precise position of mutation in the near future. We are sequencing the coding exon of alph8 connexin gene of this mutant. Conclusion: Generation and identification of cataractous mouse mutants from ENU induced mutagenesis is one of the most powerful ways to identify genes that play an essential role in the lens development and in maintaining lens transparency. The BEML1 is likely to be a novel mutation that controls the lens osmotic balance. The function of the mutant protein might be related to the regulation of connexins in the lens. Identification of this mutation and other mutations that we have identified will provide us additional insights into the lens biology. 1A authors equally contributed to this study.

Keywords: cataract • animal model • genetics