Ej. Sanders et al., CELL-DEATH IN THE GASTRULATING CHICK-EMBRYO - POTENTIAL ROLES FOR TUMOR-NECROSIS-FACTOR-ALPHA (TNF-ALPHA), Cell death and differentiation, 4(3), 1997, pp. 188-199
We have examined the expression of TNF-alpha and its receptors, TNFR1
and TNFR2, during gastrulation in the chick embryo, and have investiga
ted the possible role of this factor in the control of cell death at t
his early stage of development. TNF-alpha, immunoreactive at approxima
tely 17 kD, was found both in vivo and in vitro, most intensely associ
ated with the cell surface and cytoskeleton of endoderm cells. TNFR2 w
as especially immunoreactive in endoderm cells of the marginal zone. T
NFR1 was found in nuclei throughout the embryo. Embryos also showed wi
despread expression of both the bcl-2 and Bar gene products, which are
both associated with cell death pathways. Intact embryos in culture w
ere sensitive to the addition of TNF-alpha (approx. 110 ng/ml), respon
ding by significantly increasing the incidence of DNA fragmentation in
cells from all tissues of the embryo. This effect was abrogated by im
munological pre-absorption of the cytokine. Cultured cells from these
embryos also responded to the addition of agonistic antibodies to TNF-
alpha receptors by increasing DNA fragmentation. A similar response to
TNF-alpha antiserum by cultured cells appeared to be related to a con
comitant decrease in cell-substratum adhesion caused by the antibody.
Decreased cell adhesion, induced non specifically with antiintegrin an
tiserum, also resulted in increased DMA fragmentation. TNF-alpha, synt
hesized and secreted by the embryo itself, may be able to exert a para
crine effect on the incidence of cell death in tissues of the embryo,
and the cell death process may be related to the expression of bcl-2 a
nd Bax gene products. The influence of TNF-alpha may be exerted by the
activation of cell death signalling pathways directly, or indirectly
through perturbation of the cytoskeleton or of integrin mediated cell
adhesion.