Dynamics of Ubiquitin Pools in Developing Sea Urchin Embryos |
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Authors: | Cecile M Pickart Robert G Summers Hyunbo Shim Eileen M Kasperek |
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Institution: | Department of Biochemistry, School of Medicine, Biomedical Sciences, SUNY at Buffalo, NY 14214;Department of Anatomical Sciences, School of Medicine, Biomedical Sciences, SUNY at Buffalo, NY 14214 |
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Abstract: | The sea urchin embryo is a closed metabolic system in which embryogenesis is accompanied by significant protein degradation. We report results which are consistent with a function for the ubiquitinmediated proteolytic pathway in selective protein degradation during embryogenesis in this system. Quantitative solid- and solution-phase immunochemical assays, employing anti-ubiquitin antibodies, showed that unfertilized eggs of Strongylocentrotus purpuratus have a high content of unconjugated ubiquitin ( ca . 8 × 108 molecules), and also contain abundant conjugates involving ubiquitin and maternal proteins. The absolute content of ubiquitin in the conjugated form increases about 13-fold between fertilization and the pluteus larva stage; 90% or more of embryonic ubiquitin molecules are conjugated to embryonic proteins in hatched blastulae and later-stage embryos. Qualitatively similar results were obtained with embryos of Lytechinus variegatus . The results of pulse-labeling and immunoprecipitation experiments indicate that synthesis of ubiquitin in S. purpuratus is developmentally regulated, with an overall increase in synthetic rate of 12-fold between fertilization and hatching. Regulation is likely to occur at the level of translation, since others have shown that levels of ubiquitin-encoding mRNA remain virtually constant in echinoid embryos during this developmental interval. The sea urchin embryo should be a useful system for characterizing the role of ubiquitination in embryogenesis. |
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