The human hyaloid system: Cell death and vascular regression

The present study had investigated the roles of apoptosis and necrosis in t he regression of the human fetal hyaloid vasculature. Normal human fetal hy aloid specimens (n = 67) ranging from 10 to 20 weeks' gestation were studie d. Specimens were either immunolabeled with anti-non Willebrand factor and major histocompatibility complex class I antibodies or in investigated usin g the terminal-deoxyribonucleotidyl transferase-mediated dUTP-biotin DNA ni ck-end labeling technique. A fluorescent DNA-binding dye acridine orange/et hidium bromide mixture was also applied to unfixed flat mounts of hyaloid v asculature and some specimens were processed for transmission electron micr oscopy. Vascular regression including cell loss in the connecting vessels, stretching and thinning of the vasa hyaloidea propria, tunica vasculosa len tis and the pupillary membrane was clearly evident after 13 weeks' gestatio n. Cresyl violet staining revealed condensed cells and pyknotic bodies thro ughout the hyaloid system; cell death occurred either in single cells or al ong small capillary segments associated with vascular regression. Acridine orange/ethidium bromide staining showed DNA condensation at early and late stages of cell death. Similarly, DNA nick-end labeling was positive in endo thelial cells, pericytes and vessel and non-vessel associated hyalocytes. T he observation of hyalocytes juxtaposed to cytolysed endothelial cells may indicate a role for these cells in Vascular regression. Features of apoptos is were more evident during early vascular regression whilst necrosis was i ncreasingly evident at later stages. (C) 2000 Academic Press.