Inherited retinal degeneration and apoptosis in mutant zebrafish

摘要

abstract_textpThe mechanism of retinal cell death was studied in mutant zebrafish (Danio rerio) which undergo inherited degeneration of the retina and the brain. The shrunhen head (shr(m33)) mutation was isolated as part of a large scale mutagenesis screen. The yellow head (yhd) mutation arose spontaneously among inbred wild type zebrafish. Although the mutants share many morphological features, including small eyes, a small brain and an enlarged pericardial sac, crossing shr(m33) and yhd heterozygotes results in phenotypically normal fish./ppThe retinae of both mutant lines of fish begin to develop normally and then undergo massive degenerative changes. Pyknotic cells first appear in the retina of the shr(m33) fish by 3 days post-fertilization and in the yhd fish by 1.5 days post-fertilization. By 5 days post-fertilization the outer nuclear layer containing the photoreceptor cells has largely disappeared in both mutants. The inner nuclear layer and ganglion cell layer are also severely affected. By 6-7 days post-fertilization, the retina has been largely cleared of pyknotic cells by retinal pigment epithelial cells and by rare macrophagelike cells. Both mutations are lethal by 7-8 days post-fertilization./ppTwo independent measures, TdT-mediated dUTP-biotin nick end label (TUNEL) and transmission electron microscopy, indicate that the pyknotic cells in the mutant retinae are apoptotic. Apoptosis is very rarely observed during normal development of the teleost retina and was not observed in age-matched wild type zebrafish retinae examined for comparison. Our results indicate that a genetic defect can induce massive apoptosis in cell populations that do not normally undergo apoptosis during development. Anat Rec 258:145-155, 2000. (C) 2000 Wiley-Liss, Inc./p/abstract_text