APOPTOSIS DURING MACROPHAGE-DEPENDENT OCULAR TISSUE REMODELING

We have characterized the nature and pattern of cell death during regr ession of the pupillary membrane, a developmentally transient capillar y network found in the anterior chamber of the eye. This analysis has revealed that the cellular components of the pupillary membrane includ e vascular endothelial cells in an intricate network of fine capillari es as well as attendant macrophages. The capillaries are situated on t he anterior surface of the lens and held in relative position by a cob web-like meshwork of extracellular matrix fibres that regress along wi th the cellular components of this structure, Cell death during regres sion of the pupillary membrane is characteristic of apoptosis, Specifi cally, apoptotic bodies containing condensed chromatin can be observed in vascular endothelial cells and genomic DNA isolated from the pupil lary membrane shows the nucleosomal fragmentation pattern typical of a poptotic cells. Using a method for labelling fragmented DNA in tissue preparations (TUNEL), we have assessed the overall pattern of apoptoti c cell death during pupillary membrane regression, We find that apopto sis occurs either in single cells in healthy vessels or synchronously along the entire length of a capillary segment, Both morphological and TUNEL analysis indicate that capillary regression occurs from junctio n to junction one segment at a time, We propose a model to explain the pattern of capillary regression observed and conclude from these and previous experiments (Lang and Bishop (1993) Cell 74, 453-462), that d uring regression of the pupillary membrane, the macrophage elicits tar get cell death by inducing apoptosis,