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Transforming growth factor beta1 and beta2 reduce the number of gonocytes by increasing apoptosis
R Olaso1, C Pairault, B Boulogne
1INSERM-INRA U 418, Université Paris 7, France.
Abstract:
Transforming growth factors beta1 and beta2 (TGFbetas) have recently been detected by immunohistochemistry in the fetal and neonatal rat testis, and the aim of the present study was to determine whether these factors can act as local regulators to control the number of gonocytes. Testes were kept in organ culture, and TGFbeta1 was found to have dose-dependent inhibitory effect on the number of gonocytes in testes explanted on fetal day 13.5. Either TGFbeta1 or beta2 at 10 ng/ml reduced the number of gonocytes by half after 2 days culture. TGFbetas did not decrease the BrdU labeling index of gonocytes or Sertoli cells, whereas these factors significantly increased the DNA fragmentation in gonocytes (TUNEL method). The other testicular cell types showed no positive TUNEL reaction. TGFbeta1 did not reduce the number of gonocytes in testes explanted on fetal day 17.5 (i.e. during the quiescent phase), but it did so in testes explanted on postnatal day 3 (i.e. stage of resumption of mitosis). To determine the potential cell type targets for TGFbetas, type I and type II TGFbeta receptors were immunolocalized in developing testis from fetal day 13.5 to postnatal day 3. Both receptors were present in the gonocytes throughout the whole period studied, and in the Leydig cells from fetal day 16.5 onward, but they were not detected in the Sertoli cells. Taken together, these results suggest that TGFbetas directly increase apoptosis in gonocytes without changing their mitotic activity during the developmental phases of proliferation.
Insights
Transforming growth factors beta (TGFbetas) induce apoptosis in fetal rat gonocytes, reducing their numbers. These factors do not affect mitotic activity but increase DNA fragmentation, suggesting a direct role in gonocyte regulation.
Area of Science:
- Reproductive Biology
- Developmental Biology
- Cell Biology
Background:
- Transforming growth factors beta (TGFbetas) are present in the fetal and neonatal rat testis.
- The role of TGFbetas in regulating gonocyte numbers requires further investigation.
Purpose of the Study:
- To determine if TGFbetas act as local regulators controlling gonocyte numbers in the developing rat testis.
- To investigate the mechanism by which TGFbetas influence gonocyte proliferation and survival.
Main Methods:
- Organ culture of fetal and neonatal rat testes.
- Immunohistochemistry to detect TGFbeta receptors (Type I and II) in testicular cells.
- Analysis of gonocyte proliferation (BrdU labeling) and apoptosis (TUNEL assay).
Main Results:
- TGFbeta1 exhibited a dose-dependent inhibitory effect on gonocyte numbers in testes explanted on fetal day 13.5.
- Both TGFbeta1 and TGFbeta2 significantly increased DNA fragmentation in gonocytes, indicating apoptosis.
- TGFbetas did not affect the proliferation of gonocytes or Sertoli cells but induced apoptosis in gonocytes during specific developmental windows.
- TGFbeta receptors were found in gonocytes and Leydig cells, but not Sertoli cells.
Conclusions:
- TGFbetas directly promote apoptosis in rat gonocytes, contributing to the regulation of their population during development.
- The effect of TGFbetas on gonocyte numbers is dependent on the developmental stage, impacting proliferation phases more significantly.
- Gonocytes are direct targets of TGFbetas, as indicated by the presence of TGFbeta receptors and increased apoptosis.