T-3 TREATMENT INCREASES MITOSIS, THEN BAX EXPRESSION AND APOPTOSIS INTHE OPTIC LOBE OF THE CHICK-EMBRYO

We investigated Tg effects on cell proliferation and apoptosis in the optic lobe of the chick embryo between embryonic days (E) 6 and 11. In jection of T-3 into the yolk increased [H-3]thymidine incorporation be tween E7 and E9. This increased mitosis was followed by altered timing and degree of apoptosis during E9-11. In T3-treated embryos a marked increase in apoptosis occurred on E10, coincident with increased level s of mRNA encoding Pax, a pro-apoptotic protein. By E11, the overall m orphology and total number of cells in each layer of the optic lobe we re not different in control and treated embryos. Thus, although T-3 tr ansiently increases cell number, a homeostatic mechanism enters into p lay re-adjusting the balance between cellular proliferation and cell d eath. (C) 1997 Elsevier Science Ireland Ltd.