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K.S. Wang, L. Zahn, J. Favor, D. Stambolian; Refinement in Mapping of the Mouse Tcm Mutation; an Animal Model for Microphthalmia / Anophthalmia . Invest. Ophthalmol. Vis. Sci. 2003;44(13):1087.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Tcm (total cataract with microphthalmia) is an autosomal dominant mouse mutation recovered from an X-irradiated mouse. Initial characterization of the heterozygous Tcm mouse revealed total lens opacity, microphthalmia, iris dysplasia, and ventral coloboma. We have now characterized the homozygous Tcm phenotype which results from a failure of ventral retinal development, leading to retinal dysplasia and subsequent anophthalmia. We also present the use of a mouse backcross breeding strategy with analysis of over 270 resultant progeny to provide a refinement in mapping of the Tcm locus. Methods: Tcm heterozygous mice were outcrossed to strain C57BL/6. Resultant Tcm +/- were backcrossed to strain C57BL/6. Backcross progeny were examined and typed by slit lamp examination. PCR of genomic DNA samples was carried out for D4Mit microsatellite markers polymorphic between the two strains. Reaction products were electrophoresed and analyzed for recombinations. Recombination fractions between the Tcm locus and each of the D4Mit markers were determined by counting the number of recombinations over the number of progeny analyzed. For histopathology studies, whole embryos or brains of postnatal mice were fixed, serially sectioned, stained, and analyzed using standard methods for light microscopic examination. Results: Using a mouse backcross breeding strategy to analyze microsatellite markers D4Mit101, D4Mit106, D4Mit235, D4Mit263, and D4Mit264, we have localized Tcm to a 1.3 Mb region on mouse chromosome 4. This region is delineated by D4Mit235 and D4Mit101 with Tcm mapping approximately 0.36 cM and 0.4 cM from each marker, respectively. The homozygous Tcm eye phenotype can be seen as early as day E10 as a delay in optic cup formation and later as a failure in ventral patterning of the optic cup. Tcm homozygous adult mice are uniformly anophthalmic. Approximately 1 in 30 Tcm mice also display hydrocephalus, cerebellar defects, white matter cysts, and absence of the septum pellucidum. Conclusions: An anatomical and histological survey of the homozygous Tcm mouse indicates that severe abnormalities occur in the developing Tcm eye as early as day E10. Future experiments will aim to further clarify the natural history and pathology of this mutation. We have narrowed the Tcm locus to a 1.3 Mb region on mouse chromosome 4. Known and predicted candidate genes that map to the Tcm locus are now being analyzed by sequencing and gene expression techniques.
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