EXPRESSION OF TUMOR-NECROSIS-FACTOR-ALPHA (TNF-ALPHA)-CROSS-REACTIVE PROTEINS DURING EARLY CHICK-EMBRYO DEVELOPMENT

We have investigated the expression of tumor necrosis factor-alpha (TN F alpha)cross-reactive proteins during the early development of the ch ick embryo from day 1 to day 6 (H-H stages 5-29) using a polyclonal an tibody and two monoclonal antibodies to recombinant mouse TNF alpha. W e have confirmed the cross-reactivity of the antibodies with chicken t issue in Western blotting studies. Proteins of 50 kDa and 70 kDa, show ing anti-TNF alpha cross-reactivity, have been identified during early chick development. In addition, both monoclonal antibodies recognize a 120 kDa protein. These molecules probably represent cytosolic or tra nsmembrane TNF-alpha-like proteins, similar to those previously identi fied on the surface of cytotoxic T-lymphocytes. We show by ultrastruct ural cytochemistry that immunoreactivity can be detected at the surfac es of some cells, suggesting that at least some of the antigen is memb rane-associated. The proteins are shown to have a widespread tissue di stribution during this period of development. Immunoreactivity is firs t detected in the gastrulating embryo, in the mesoderm and the endoder m. By day 2, expression is confined to the ectoderm and the endoderm, while at day 3 expression appears in the myotome, the notochord, and i n nervous tissue. At day 4 the distribution of reactivity is more exte nsive and includes the notochord, the sclerotome, and the myotome, whi le the cranial and spinal nerves also become intensely immunoreactive. Also at this stage, neural tube reactivity becomes localized to the m arginal neuroepithelial zone, and the lens fibers become positive. Thi s distribution of staining then persists until 6 days of development. We hypothesize that the expression of TNF alpha-cross-reactive protein s in early development could be indicative of a role for them in progr ammed cell death (apoptosis) during differentiation of the notochord, the lens, and the nervous system, and in tissue remodeling. (C) 1993 W iIey-Liss, Inc.