Function of TGF-beta2 in the growth of chicken primordial germ cells and germinal ridge stroma cells during embryonic development

The development of chicken embryonic gonads is locally regulated by the systematic action of growth factors. Recently, we used suppressive subtraction cloning to identify transforming growth factor beta2 (TGF-beta2) as a growth factor gene preferentially expressed in chicken embryonic ovaries and testes during the early periods of development (Hattori et al. 2002a. Prominent expression of transforming growth factor beta2 gene in the chicken embryonic gonad as revealed by suppressive subtraction cloning. Gen Comp Endocrinol 125:311-316). In the present study, the function of TGF-beta2 in chicken embryonic gonads was investigated using a serum-free culture system in the presence of several growth factors, which may behave as mitogenic or survival factors of primordial germ cells (PGCs). Chicken germinal ridges containing PGCs and germinal ridge stroma cells (GRSCs) were collected from six-day embryos. Addition of TGF-beta2 caused a dose-dependent inhibition of the number of co-cultured PGCs and GRSCs in the presence of these growth factors. However, there was no obvious difference between embryonic ovaries and testes in the effects of TGF-beta2. Immunocytochemical analysis using anti-SSEA-1 antibody revealed that TGF-beta2 induced fragmentation of PGCs. Expression of the TGF-beta2 gene was estimated in the co-cultured PGCs and GRSCs by semi-quantitative RT-PCR. The mRNA level of TGF-beta2 was significantly suppressed in the presence of the growth factors. These results suggest that TGF-beta2 is a gonadal regulator preferentially expressed at the early stages of chicken embryonic development and reduces the growth of PGCs and GRSCs by suppressing proliferation. However, expression of TGF-beta2 may be controlled by mitogenic or survival factors of PGCs.