Synthesis of a posterior indicator protein in normal embryos and double abdomens of Smittia sp

In embryos of the chironomid midge Smittia, synthesis of a posterior indicator protein designated PI1 forecasts development of an abdomen as opposed to head and thorax. In normal embryos at early blastoderm stages, synthesis of PI1 is restricted to posterior embryonic fragments but not to pole cells. In double-abdomen embryos, a mirro-image duplication of the abdomen is formed by cells that would otherwise develop into head and thorax. Embryos were prorammed for double-abdomen development by uv irradiation of the anterior pole, and half of them were reprogrammed for normal development by subsequent exposure to visible light (photoreversal). Correspondingly, PI1 was synthesized in anterior fragments of uv-irradiated embryos but not after photoreversal. The identity of PI1 was revealed by two-dimensional gel electrophoresis and limited proteolysis. Suppression of PI1 synthesis in anterior fragments of normal embryos is ascribed to the activity of cytoplasmic ribonucleoprotein particles thought to act as anterior determinants