Posttranslational modifications as a cause of gonadal polypeptide diversity in the rat

The testicular and ovarian protein patterns of prepubertal rats were studied by two-dimensional gel electrophoresis after both in vivo and in vitro translation. Analysis of the approximately 750 polypeptide spots detectable in gonadal extracts (in vivo translated polypeptides) revealed 14 testis-specific, and 2 ovary-specific spots. Conversely, only 4 testis- and 2 ovary-specific polypeptide spots (of a total of about 600) were detected after in vitro translation of the respective polyadenylated RNAs using the reticulocyte lysate system. Simultaneous in vitro translation plus microsome-mediated cotranslational modification increased the number (of testicular spots to 8, and of ovarian spots to 3 (of a total of 600). The polypeptides synthesized in vitro were well comparable with respect to molecular weight and isoelectric point to those synthesized in vivo. Therefore, testicular polypeptide diversity is mainly the result of co/posttranslational modifications. Many of these proteins appeared to be glycosylated as indicated by their specific binding to Concanavalin A. The system used demonstrates that co/posttranslational modifications play a role in the establishment of polypeptide and thus organ diversity.