Expression of Basic Fibroblast Growth Factor-Like Substance in Immature Rat Testis: Immunocytochemical Localization and Detection of mRNA

We have previously described immunoreactive basic fibroblast growth factor (bFGF)-like substance in adult rat testis and have shown that this bFGF-like substance presents in the nucleus of germ cells. In the present study, the distribution of bFGF was examined immunohistochemically in 3 or 12-day-old rat testes. In 3-day-old, immunoreactivity for bFGF was detected in the cytoplasm of gonocytes (prespermatogonia) and fetal Leydig cells. In contrast, in 12-day-old, immunoreactivity for bFGF was detected exclusively in the nucleus of germ cells. Thus, bFGF seems to translocate from the cytoplasm to the nucleus during formation of the first wave of spermatogenesis. Using reverse transcription-polymerase chain reaction (RT-PCR), bFGF mRNA was detected in the 3-day-old rat whole testis. Moreover, in situ hybridization analysis revealed gonocytes and fetal Leydig cells contain mRNA for bFGF. These results indicate that bFGF is synthesized in gonocytes and fetal Leydig cells before the formation of the first wave of spermatogenesis.