DISTRIBUTION OF TNF-ALPHA-LIKE PROTEINS CORRELATES WITH SOME REGIONS OF PROGRAMMED CELL-DEATH IN THE CHICK-EMBRYO

Early chick embryos have previously been shown to express tumor necros is factor-alpha-cross-reactive proteins (TNF alpha-CRPs) in a developm entally regulated manner, thus implicating these proteins in programme d cell death and in tissue remodeling. In this study, cells undergoing DNA fragmentation have been identified, using terminal deoxynucleotid e transferase (TdT) mediated dUTP-biotin nick-end-labeling (TUNEL), du ring the embryonic development of the chick, between stages 18 and 29. DNA fragmentation is indicative of cells undergoing programmed cell d eath. TUNEL-positive cells were identified in several well documented areas of programmed cell death, including the limb buds, the heart, sp inal motoneurons, dorsal root ganglia, and the ventral horn of the neu ral tube. In addition, other areas of cell death were identified inclu ding the floor plate a nd the mesonephros. In several locations, a clo se correlation was noted between the presence of TUNEL-positive cells and regions of TNF alpha-immunoreactivity. These regions included the ventral horn and marginal zone of the neural tube, spinal motoneurons, paravertebral ganglia, parts of the myotome, mesenchyme of the body w all, and the mesonephros. In addition, using the TNF alpha-sensitive L 929-8 bioassay it was shown that homogenate of stage 18 chick embryos is cytotoxic to L929-8 cells and that this toxicity can be reduced usi ng neutralizing antibodies to mouse TNF alpha. This bioassay allowed u s to estimate the mean concentration of TNF alpha-like activity in emb ryo homogenate, which is within the range of physiological (pg/ml) lev els of TNF alpha found in other systems. These results suggest that pr oteins with TNF alpha-like activity may have a role in programmed cell death in some tissues during early chick embryo development.