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 necrosis factor-alpha-cross-reactive proteins (TNF alpha-CRPs) in a developmentally regulated manner, thus implicating these proteins in programmed cell death and in tissue remodeling. In this study, cells undergoing DNA fragmentation have been identified, using terminal deoxynucleotide transferase (TdT) mediated dUTP-biotin nick-end-labeling (TUNEL), during the embryonic development of the chick, between stages 18 and 29. DNA fragmentation is indicative of cells undergoing programmed cell death. TUNEL-positive cells were identified in several well documented areas of programmed cell death, including the limb buds, the heart, spinal motoneurons, dorsal root ganglia, and the ventral horn of the neural tube. In addition, other areas of cell death were identified including the floor plate and the mesonephros. In several locations, a close 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 wall, and the mesonephros. In addition, using the TNF alpha-sensitive L929-8 bioassay it was shown that homogenate of stage 18 chick embryos is cytotoxic to L929-8 cells and that this toxicity can be reduced using neutralizing antibodies to mouse TNF alpha. This bioassay allowed us to estimate the mean concentration of TNF alpha-like activity in embryo homogenate, which is within the range of physiological (pg/ml) levels of TNF alpha found in other systems. These results suggest that proteins with TNF alpha-like activity may have a role in programmed cell death in some tissues during early chick embryo development.