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M.R. Fischette, X. MA, C.–C. Chan, R. Adelstein; Abnormalities in the retinas of mice with a single amino acid mutation in nonmuscle myosin II–B . Invest. Ophthalmol. Vis. Sci. 2004;45(13):3545.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Nonmuscle myosin II proteins, the conventional form of myosin present in most eukaryotic cells, are active in the contractile process during embryonic development as well as later life. These proteins contribute to the mechanisms by which cells migrate, change their shape and undergo cytokinesis. To study the in vivo function of the three isoforms of the nonmuscle myosin heavy chain (NMHC), II–A, II–B, and II–C, we have generated mice that have been ablated for the NMHC II–B gene product, as well as mice harboring a single amino acid mutation in NMHC II–B. This mutation, in which Arg709 was replaced by Cys (R709C) was introduced to produce a putative mouse model for human retinal disease. Previous work from this laboratory showed that ablation of NMHC II–B resulted in rosette formation in the retina just prior to birth (J Comp Neurol 433:62–74. ) Here we report on the C/C and R/C mice. Methods: Transgenic mice were generated by homologous recombination. The point mutation R709C was introduced into exon 17. After generation of heterozygous ES cells the mutation was confirmed by nucleotide sequencing and positive ES cell clones were injected into blastocysts from C57BJ/6 mice. Eyes were enucleated from newborn myosin–IIB knockout mice, and from adult R/R and R/C knockin mice. Embryos were obtained at day E14 from knockout, R/R, and C/C knockin mice as well as from adult R/C mice. All specimens were formalin–fixed and paraffin embedded for routine histology. Immunohistochemistry was performed using antibodies to nonmuscle myosin–IIA, –IIB, –IIC, GFAP and NSE. Results: Eyes taken from embryos of R/R and C/C mice showed no morphological differences; however C/C mice die at E14.5 due to cardiac and brain defects, preventing further study. The retinas from adult R/C mice showed an increase in the number of nuclei in the inner plexiform layer as well as retarded migration of the ganglion cells. This suggests a possible arrest in retinal cell migration. Immunohistochemistry demonstrated similar levels and patterns of staining for nonmuscle myosin–IIA on vessels and a low expression of nonmuscle myosin–IIC in the retina. Conclusions: Adult R/C mice with a single amino acid mutation in NMHC II–B show abnormalities in neuronal cell migration in the adult retina. The significance of these findings has yet to be determined, but since it is likely that, similar to mice, only humans that are heterozygous for this mutation will survive, it will be of interest to see if humans bearing a mutation in NMHC II–B manifest similar abnormalities in their retinas.
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