PubMed · 3713761
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U C Dräger. 1986-06-19. Albinism and visual pathways.. https://doi.org/10.1056/nejm198606193142508
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The central retina in albino mammals is poorly developed. There is a general reduction in ganglion cell density compared with the normal animal, and there are irregularities in the center to periphery gradient in ganglion cell density. It is not known whether, and if so to what extent, this abnormality is associated with deficits in other retinal layers. In this study the distribution of cells in the ganglion cell layer has been determined in horizontally sectioned eyes from pigmented and albino ferrets. This was undertaken to define the location of the region of highest cell density and the relative cell gradients around it. Detailed counts and measurements were then undertaken to determine the cell density within, and thickness of, the inner and the outer nuclear layers in these animals. All the albino animals had an abnormal distribution of cells in the ganglion cell layer in the central retina when compared with pigmented animals. The extent of this abnormality was variable. No differences between pigmented and albino animals could be found in the packing density of cells within the inner or the outer nuclear layer. However, in the pigmented animals there was a clear increase in the thickness of these layers associated with the region of highest density in the ganglion cell layer. This feature was absent in the albino animals, where the gradient in layer thickness was less marked and frequently contained irregularities. These abnormalities were most obvious in the outer nuclear layer.
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Several overlapping chromosomal deletions spanning the albino locus in the mouse cause perinatal lethality when homozygous and a block in the transcriptional induction of various unlinked hepatocyte-specific genes. Studies of such lethal albino deletion homozygotes in perinatal stages revealed a deficiency in the transcriptional inducibility of the tyrosine aminotransferase (TAT) gene by glucocorticoids; yet, glucocorticoid receptor and hormone levels were shown to be unaffected. To identify a molecular defect underlying the failure of inducible expression, we examined the chromatin structure of the TAT gene. Whereas in wild-type animals the TAT promoter becomes DNase I hypersensitive at birth, such hypersensitivity fails to develop in lethal albino deletion homozygotes. By contrast, the deletions do not affect the appearance of three DNase I-hypersensitive sites upstream of the TAT promoter in the liver, nor do they affect two hypersensitive sites upstream of the expressed alpha-fetoprotein gene. These findings demonstrate that the abnormality of chromatin structure identified in lethal albino deletion homozygotes occurs on a highly selective basis. Specifically, normal differentiation of the TAT promoter chromatin appears to depend directly or indirectly on the action and product of a gene mapping within the deleted region.