Analysis of the retinal neuroepithelium in young mutants. (A) Transverse retinal sections of 32 hpf wild-type (left) and young (right) embryos probed for rx2 transcript expression. No differences in expression patterns or levels were detected between wild-type and mutants at 32 hpf or earlier. (B) Immunoreactivity for γ-tubulin localizing the centrioles in the retina (arrowheads) and brain (arrows) of two embryos at 24 hpf. Centrioles were found to localize to apical positions in all embryos resulting from young heterozygous matings. At 24 hpf, mutant and wild-type embryos could not be consistently distinguished. (C) BrdU incorporation (red) from 62 hpf until 74 hpf when embryos were fixed for assessment of zn-12 expression. Sagittal sections, anterior up, dorsal right, of wild type (left) and young (right). In sagittal section the wave of retinal cell birthdating can be viewed in the ventral to dorsal sweep as well as from inside to outside. Note that cell proliferation has nearly ceased by 62 hpf in the wild type, while significant numbers of mutant cells destined for the outer retina, particularly in the dorsal region, continue to divide. (D). BrdU incorporation (74 hpf injection, 96 hpf fixation; red label) and zn-12 immunoreactivity (green label) in transverse sections reveal that only marginal zone cells are proliferating. Young retinoblasts (right) have exited the cell cycle similar to those in wildtype siblings (left).
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