Analysis of mechanism of changes in function and size of golden hamster testis with special reference to TGF-β signal transduction

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First, during prespermatogenesis when the testis prominently increases in size, the reproliferation and relocation of gonocytes were examined by BrdU method and electron microscopy. Gonocytes began to move from 17.5dpc and relocated on the basement membrane from 18.5dpc. BrdU-labeled gonocytes were first detected on 1.5dpp. They increased in number abruptly from 2.5dpp and then gradually increased. Secondly, histology and lectin-binding patterns in the testes of two different-body sized bats (Java fruit bat, average b.w. : 567g ; Japanese lesser horseshoe bat, average b.w. : 7g) were investigated. Both testicular morphology and lectin-bindig patterns were almost similar between these two species. Thirdly, the mouse Smad3 cDNA including the open reading frame was cloned from the mouse brain using RACE technique, and its expression pattern was analyzed by northern blot. The predicted amino acid sequences of mouse Smad3 showed a high homology with human Smad3 (99.3%) and mouse Smad2 (85.4%). Northern blot analysis revealed that Smad3 was highly expressed in brain and ovary. In situ hybridization revealed that Smad3 was detected in pyramid cells of hippocampus, granular cells of cerebral cortex, and granulosa cells of ovary. Next, the expression of Smad2 and Smad3 mRNA was examined under the influence of long and/or short photoperiod in hamsters. In situ hybridization detected both Smad2 and Smad3 mRNA in spermatogonia and spermatocytes in both photoperiods. Northern blots showed that Smad2 mRNA was detected at all stages in both photoperiods, whereas Smad3 mRNA was expressed in a short photoperiod. The photoperiodic condition would change the balance between Smad2 and Smad3 transcripts. Moreover, the localization of Smad2 and Smad3 protein was examined in both photoperiods. The Smad2 and Smad3 proteins were localized in spermatocyte cytoplasm in a long photoperiod. They accumulated in spermatocyte nucleus in a short photoperiod.