| Abstract: | The transforming growth factor β (TGF‐β) superfamily members are important molecules that regulate many ovarian functions under normal physiological and pathological conditions. TGF‐β1 and its receptors are highly expressed in the ovarian cells of many species. However, the effect of TGF‐β1 on the capacity of the avian germ cell reservoir remains unknown. In this study, 5‐day‐old chicks were injected with TGF‐β1 (2.5, 12.5, and 62.5 μg/kg body weight) for 3 days to assess the effect of TGF‐β1 on early follicle development. Morphological analysis showed that treatment with TGF‐β1 (12.5 μg/kg) increased the number of germ cell cysts and reduced the number of primordial and growing follicles. The diameter and area of oocytes and follicles were decreased after TGF‐β1 treatment. Immunohistochemical staining of the proliferating cell nuclear antigen revealed that the ratios of the positive somatic and granulosa cells were decreased by 16.2% and 2.48%, respectively. Furthermore, more apoptotic cells were observed in the TGF‐β1 group than those of the control by terminal deoxynucleotidyl transferase dUTP nick end labeling assay. In addition, we cultured the 5d chicken ovaries for 3 days in vitro and found that treatment with TGF‐β1 (10 ng/mL) manifested similar results as the in vivo experiment. However, the negative effect of TGF‐β1 on early ovary development was rescued by treatment with a TGF‐βR1 inhibitor SD208, resulting in increased expression of steroidogenic enzymes and cell cycle‐regulating proteins. In conclusion, TGF‐β1 could maintain the germ cell reservoir by restraining follicle activation involving reduced cell proliferation and steroidogenic enzymes gene expression at the early stage of ovarian development. |
