CELL-DEATH IN THE AVIAN BLASTODERM - RESISTANCE TO STRESS-INDUCED APOPTOSIS AND EXPRESSION OF ANTI-APOPTOTIC GENES

We investigated the expression of an apoptotic cell death program in b lastodermal cells prior to gastrulation and the susceptibility of thes e cells to stress-induced cell death, A low frequency (3.1%) of apopto tic blastodermal cells was observed in Hoechst 33342-vitally stained c ytological preparations of complete blastoderms from unincubated eggs. These cells showed the stereotypic features of apoptosis including a progression of nuclear changes, cell shrinkage and blebbing, and the f ormation of apoptotic bodies. Prolonged storage of eggs at 12 degrees C induced apoptosis in blastodermal cells (14%). A modest amount of ap optosis (10%) was also induced at the heat shock temperature of 48 deg rees C, but not at 45 degrees C, Etoposide and other potent cytotoxic drugs failed to induce apoptosis in the blastodermal cells after 4 h o f exposure. Progressively more apoptosis was induced at 8 and 24 h, bu t it did not exceed 35% of the cells. We detected transcripts for the anti-apoptotic genes bcl-2, bcl-x(L), and hsp70. The developmental exp ression of these genes, especially hsp70, correlated with the delayed and limited stress-induction of apoptosis. These studies reveal the ca pacity of pre-streak blastodermal cells to engage in apoptosis and the ir relative resistance to stress conditions. This may be due to the pr ominent expression of hsp70 and/or multiple cell death genes which pri marily antagonize cell death.