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Smriti Akshaya Agrawal, Atul Kakrana, Christine Dang, David A Scheiblin, Stephanie Waters, Abhyudai Singh, Hozumi Motohashi, Salil Anil Lachke; Characterization of lens defects in mouse mutants of bZIP transcription factors MafG and MafK. Invest. Ophthalmol. Vis. Sci. 2014;55(13):745.
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© ARVO (1962-2015); The Authors (2016-present)
Function of the large Maf transcription factor MAF (c-Maf), a basic leucine-zipper protein, in fiber cell differentiation and its association with inherited juvenile cataract is well established. However, the function of small Maf proteins in the lens or their connection to cataract has not been investigated. Here, we report on the characterization of mouse mutants carrying null alleles of small Mafs MafG and MafK, and their function in lens homeostasis and maintenance of transparency.
iSyTE (integrated Systems Tool for Eye gene discovery) was used to identify MafG as a highly enriched transcriptional regulator gene in the lens. To validate this prediction, we generated MafG:MafK compound mutant mice for phenotypic and molecular characterization. Immunofluorescence and in situ hybridization were performed to detect small Mafs expression in lens fiber cells. Dark-field and grid- imaging, scanning electron microscopy, and histological analysis were performed to characterize morphological defects in the lens. Gene expression profiling by Illumina Mouse WG-6 microarrays was performed to identify differentially regulated genes in MafG-/-:MafK+/- mutant lens, and candidate genes were validated by qRT-PCR.
MafG-/-:MafK+/- compound mutants exhibit lens abnormalities from P60 and develop cataract marked by severe morphological fiber cell defects at ages 4-7 months. Scanning electron microscopy (SEM)-based analysis demonstrated that membrane protrusions in cortical fiber cells were abnormal in MafG-/-:MafK+/- compound mutant lens. Microarrays-based transcript profiling analysis indicated abnormal expression of stress response genes such as Ddit3, Hsp27 and Hmox1 in MafG-/-:MafK+/- compound mutant lenses. To gain insight into small Maf-mediated gene regulation, we analyzed small Maf binding sites in 2.5kb genomic region upstream of the various differentially regulated genes. We have identified several conserved ARE sites recognized by CNC/Bach and MafG/K heterodimers and are currently validating these regulatory elements.
We have characterized the function of small Maf transcription factors MafG and MafK in the lens. These regulators mediate expression of stress response genes in fiber cells, disruption of which results in cataract. These findings demonstrate that MafG and MafK function in lens homeostasis and suggest their candidacy for investigation in human cataract.
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