RESUMEN
An abundant ovarian protein with a relative mol wt (Mr) of 37K and an apparent pI of 8, associated with the onset of sexual maturity in the rabbit, has been identified. Ovaries from sexually mature (greater than 6 months old) rabbits contain large quantities of this 37K protein, while none can be detected in ovaries of immature (1 and 2 months) animals. Analysis of polyacrylamide gel electrophoresis (PAGE) gels of mature ovarian homogenates demonstrates that this protein is more abundant than actin in these preparations. It appears to be tissue specific, since it was not detected in 16 other rabbit tissues tested. Autoradiographic analysis of proteins labeled with 35S in ovarian organ culture demonstrates that a protein of identical Mr and charge to the 37K protein is synthesized in this tissue. Polyclonal sheep antiserum has been produced to the two-dimensional PAGE-purified protein. Immunoblotting of two-dimensional PAGE gels shows specific recognition of this protein and two slightly more acidic proteins of the same Mr by this antiserum. These three protein species also stain identical colors with a silver-based color stain, further suggesting that these are charge variants of the same protein. This protein is not present in corpora lutea isolated form sexually mature ovaries and is present in interstitial cell-enriched ovaries of rabbits which have been actively immunized with zona pellucida proteins. Immunocytochemical localization studies further demonstrate that this protein is localized in the interstitial gland cells. These findings suggest that this 37K protein is not associated with either follicular or luteal cells, but, rather, is linked with the 20 alpha-hydroxyprogesterone-secreting interstitial gland cell population.