Disruption of the Gene for Lens Intrinsic Membrane Protein–2 Triggers Cataract in Mice

Abstract

Abstract: : Purpose: The mouse gene for lens intrinsic membrane protein 2 (Lim2) encodes a distant relative of the peripheral myelin protein (PMP)/claudin sub–family of the tetraspanin superfamily of integral membrane proteins. Mutations in Lim2 and its human counterpart (LIM2) have been linked with autosomal dominant and recessive forms of cataract, respectively. To gain further insights about Lim2 loss–of–function we have generated Lim2–deficient mice and begun to characterize their lens development. Methods and Results: Mice were derived from a bank of gene–trap embryo stem cells and genomic DNA was prepared from tail–snips using spin–columns. Total RNA and membrane proteins were isolated from lenses using guanidinium thiocyanate and urea/detergent extraction, respectively. Genomic PCR amplification and sequencing showed that the gene–trap vector had disrupted intron 3 of Lim2 resulting in a null allele as verified by reverse–transcript (RT)–PCR amplification and sequencing, RNA blotting and immunoblotting. Mice homozygous for the gene–trap (Lim2^Gt/Gt) presented with congenital cataract when the eyes opened on postnatal day 14 (P14). At three weeks of age (P21), Lim2^Gt/Gt lenses displayed a discrete opacity centered in the fetal nuclear region. In contrast, heterozygous lenses (Lim2^+/Gt) did not develop similar opacities until around 24 weeks of age, however at P21, Lim2^+/Gt lenses displayed an optically disturbed nuclear region centered along the optical axis. Conclusions: These results suggest that heterozygous loss of Lim2 is sufficient to induce cataract in mice and that this functionally enigmatic tetraspanin plays a dosage–dependent role in establishing the refractive architecture of the crystalline lens.

Keywords: transgenics/knock–outs • cataract • gene/expression