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Thanh T. Tran, Gregoy Y. Bedecarrats, Vivian Choh; Examination of retinal cell type degeneration in embryonic Smoky Joe chickens. Invest. Ophthalmol. Vis. Sci. 2012;53(14):3957.
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© ARVO (1962-2015); The Authors (2016-present)
A genetic mutation in the pigmented White-Leghorn strain of chicken called Smoky Joe (first describe Salter et al, 1997:J Vet Diagn Invest,9: 407-9), causes inherited ocular anomalies showing varying levels of retinal degeneration and blindness at hatch. By 8 weeks post-hatch all homozygous birds are completely blind. The purpose of this study is to determine the characteristics of retinal cell degeneration in embryonic Smoky Joe (SJ) chickens.
Embryos were obtained at 5 time points: embryonic day 4 (E4), E6, E8, E14, and E18. Parent phenotypes and genotypes were used to predict sight and blindness of embryos. Entire embryos, entire globes or eyeycups were processed for sectioning. Immunohistochemistry using cell type-specific markers (Ap2α, Lim1+2, Brn3a, protein kinase Cα, glutamine synthetase, visinin, lectin wheat germ agglutinin) was used to label cells of interest (amacrine, horizontal, ganglion, bipolar, Müller, cone and rod cells, respectively), while DAPI was used to counterstain cell nuclei. Deconvolution microscopy-imaged retinas were obtained and the various cell types in the neuroblastic (outer neuroblastic [ONBL] and inner neuroblastic [INBL]) layers or nuclear (ganglion cell [GCL], inner nuclear [INL], and outer nuclear [ONL]) layers were counted.
Comparisons of the total means of cells showed significantly lower numbers in blind SJ embryos than sighted across all time points (p<0.0001; E4, blind vs sighted: 19555 ± 9347 vs 211019 ± 14285 cells/mm²; E18, blind vs sighted: 309157 ± 4,075 vs 384986 ± 18651 cells/mm²). Nuclear layers were formed at E14, and by E18 were clearly distinguishable in both blind and sighted. No differences in cell numbers were observed in the ONL or GCL across all time points but starting at E14, the number of cells in the INL was significantly lower in blind embryos (p=0.0047: blind vs sighted: 235926 ± 18162 vs 280185 ± 12534 cells/mm²). The percentages of amacrine, bipolar, and ganglion cells were on average slightly lower in blind embryos compared to sighted but no significant differences in numbers of any retinal cell types were detected across all time points (p>0.0958). Interestingly, amacrine cells developed at a later stage (E14) in blind embryos than in sighted.
Blind SJ embryos have significantly less cells during development and the INL was the site for significant cell loss. Percentages of the different retinal cells were lower in blind embryos suggesting incomplete development or possibly degeneration of these cells. This work is consistent with the finding that cell numbers in the INL are lower at hatch in blind birds than in sighted birds (Tran et al, 2010: ARVO E-Abstract 1817). It remains to be determined how these cells are affected in post-hatch birds.
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