Programmed cell death in extraocular muscle tendon/sclera recursors

Purpose: This study was designed to examine the occurrence of natural cell death in the periocular mesenchyme of mouse embryos. Methods: Vital staining with LysoTracker Red and Nile blue sulfate as well as terminal nick end labeling (TUNEL) were utilized to identify apoptotic c ell death in whole and histologicaly sectioned gestational day 10.5 to 14 m ouse embryos. Laser scanning confocal microscopy was used to provide a thre e dimensional representation of the cell death pattern. Immunohistochemical staining for neural crest and myoblast populations was utilized to indicat e the cell population undergoing apoptosis. Results: Programmed cell death was evident in the developing rectus muscle tendons/sclera on gestational days 11 through 12.5 (corresponding to the we eks 5-6 of human development). Although each of these peripheral periocular condensations has readily apparent amounts of apoptosis, the pattern of ce ll death varied among them. Cell death was most apparent in the superior re ctus tendon primordium, while that for the lateral rectus had the least evi dence of apoptosis. Conclusions: Although apoptosis was readily evident in the periocular mesen chyme in distinct regions located medial and distal to the developing rectu s muscles, programmed cell death in these sites has not previously been rep orted. New imaging techniques coupled with stains that evidence apoptotic c ell death have made it possible to define this tissue as a prominent region of programmed cell death. Although neuronal tissues, including particular regions of the developing eye, are well recognized as sites of programmed c ell death, description of this phenomenon in the extraocular tendon/sclera precursors is novel.