Synthesis of Proteins Enriched in Li

Sea urchin embryos were vegetalized by a pulse treatment with 60 mM Li+ between 2.5 hr and 6 hr after fertilization at 20°C. Normal and Li+ -treated embryos were exposed to [35 S]-methionine for 2 hr at various stages and [35 S]-labeled proteins were analyzed by two-dimensional polyacrylamide gel electrophoresis (2D-PAGE). On fluorograph of 2D-PAGE at the pre-hatching blastula stage, significant difference of labeled proteins between normal and vegetalized embryos was not observed in the range from neutral to acidic pH, but pls of several proteins were found to be shifted toward alkaline pH. At the mesechyme blastula stage, five major proteins [M.W. 36 K, 43 K (two species), 71 K and 150 K] were enriched in Li+ -treated embryos among a few hundreds of synthesized proteins. At the late gastrula stage, the labeling intensities of these proteins except for one of 43 K proteins increased remarkably in Li+ -treated embryos. Furthermore, two proteins (M.W. 105 K and 135 K) were also enriched in Li+ -treated embryos at this stage. At the prism stage, these proteins enriched in Li+ -treated embryos became hardly detectable, and the synthesis of at least four proteins (M.W. about 20 K, 41 K, 43 K and 200 K<) appeared to increase in normal embryos, but not in Li+ -treated embryos. Synthesis of proteins eniched in Li+ -treated embryos probably support endodermal cell differentiation.