Qualitative comparison of protein production at different stages of hamster preimplantation embryo development

The developmental pattern of protein production in hamster preimplantation embryos was investigated as a preliminary to studying the regulation of gene expression. Optimal radiolabelling of embryonic proteins was achieved by culturing a minimum of 40 embryos in 50 μl of Hamster Embryo Culture Medium-2 for 2 h with 10 μCi of freshly lyophilized [³⁵S]methionine. Proteins synthesized in vitro by different stages of hamster preimplantation embryos were analysed by one- and two-dimensional polyacrylamide gel electrophoresis followed by autoradiography. There were striking changes in the protein profile following the first cleavage division and also lesser changes after the second cleavage division. There were no detectable qualitative changes in the protein profiles of 4-cell, 8-cell, morula and blastocyst stages although some quantitative difference existed between morula and blastocyst stages. These comparisons of protein profiles during different stages of embryo development indicate that in hamsters the onset of embryonic gene activation occurs during the 2-cell stage.