Proto-oncogenes play an important role in the regulation of cellular growth and differentiation. C-Jun activity has been studied in the testis of a non mammalian vertebrate, the lizard Podarcis s. sicula, during two different periods: winter stasis and the breeding season. C-Jun protein was localized by immunocytochemistry in the cytoplasm of the spermatogonia (SPG) and stage I and II spermatocytes (SPC) during the winter stasis (from December until March), while the protein was present in the nuclei of the same cells during the active spermatogenic period (April/May). The different localization of c-Jun has been confirmed by Western blot and immunoprecipitation analysis. In addition, when Jun is present in the nuclear compartment, it is phosphorylated on Ser-63 and is complexed with Fos protein.These data suggest that the nuclear localization of the Jun protein in the SPG and stage I and II SPC, with strong phosphorylation on Ser-63 during the breeding period, could be the signal of increasing transcriptional activity in the lizard testis.

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