Expression of tumor necrosis factor‐α (TNFα)‐cross‐reactive proteins during early chick embryo development

We have investigated the expression of tumor necrosis factor‐α (TNFα)‐cross‐reactive proteins during the early development of the chick embryo from day 1 to day 6 (H‐H stages 5–29) using a polyclonal antibody and two monoclonal antibodies to recombinant mouse TNFα. We have confirmed the cross‐reactivity of the antibodies with chicken tissue in Western blotting studies. Proteins of 50 kDa and 70 kDa, showing anti‐TNFα 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 transmembrane TNF‐α‐like proteins, similar to those previously identified on the surface of cytotoxic T‐lymphocytes. We show by ultrastructural cytochemistry that immunoreactivity can be detected at the surfaces of some cells, suggesting that at least some of the antigen is membrane‐associated. The proteins are shown to have a widespread tissue distribution during this period of development. Immunoreactivity is first detected in the gastrulating embryo, in the mesoderm and the endoderm. By day 2, expression is confined to the ectoderm and the endoderm, while at day 3 expression appears in the myotome, the notochord, and in nervous tissue. At day 4 the distribution of reactivity is more extensive and includes the notochord, the sclerotome, and the myotome, while the cranial and spinal nerves also become intensely immunoreactive. Also at this stage, neural tube reactivity becomes localized to the marginal neuroepithelial zone, and the lens fibers become positive. This distribution of staining then persists until 6 days of development. We hypothesize that the expression of TNFα‐cross‐reactive proteins in early development could be indicative of a role for them in programmed cell death (apoptosis) during differentiation of the notochord, the lens, and the nervous system, and in tissue remodeling. © 1993 Wiley‐Liss, Inc.