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B.E. Reese, M.A. Raven, S.B. Stagg; Does Cell Death Improve Mosaic Patterning in the Population of Horizontal Cells in Mouse Retina? . Invest. Ophthalmol. Vis. Sci. 2005;46(13):576.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To determine whether the population of retinal horizontal cells undergoes an increase in mosaic regularity during development, and if so, to determine whether naturally occurring cell loss contributes to this improvement in patterning. Methods: Horizontal cells were labeled with antibodies to neurofilaments or calbindin at different developmental stages, and then visualized in retinal wholemounts using standard indirect immunofluorescence. Multiple fields were sampled from the center and the periphery of each retina to determine horizontal cell density and mosaic regularity. An estimate of total horizontal cell number was calculated for each retina, while the Voronoi domain regularity index and the packing factor were computed for each field. Two strains of mice showing a two–fold difference in the size of their horizontal cell population were sampled, C57BL/6J and A/J, at P–1, P–5 and P–10, largely encompassing the period of naturally occurring cell loss in the developing inner nuclear layer. Results: As in maturity, horizontal cell number in C57BL/6J was approximately twice that observed in A/J at all postnatal stages. The absolute number of horizontal cells in either strain during development never exceeded the value in maturity. Both the Voronoi domain regularity index and the packing factor were significantly higher than those for random, density–matched, distributions of cells at all ages, but were found to be significantly lower at P–1 relative to later developmental stages, in both strains. Conclusions: These results show that naturally occurring cell loss does not play a role in the establishment of the final number of retinal horizontal cells. They also make clear that this mechanism cannot be the cause of the strain difference in total horizontal cell number. Cell death, therefore, cannot be the cause of the increase in mosaic regularity that is observed following the day of birth in both strains. Rather, these results are consistent with the hypothesis that tangential dispersion, normally occurring in the population of horizontal cells after P–1, is the mechanism responsible for the improvement in mosaic patterning during development.
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