Kim, D. J., Seok, S. H., Baek, M. W., Lee, H. Y., Juhn, J. H., Lee, S., ... & Park, J. H. (2010). Highly expressed recombinant human follicle-stimulating hormone from Chinese hamster ovary cells grown in serum-free medium and its effect on induction of folliculogenesis and ovulation. Fertility and sterility, 93(8), 2652-2660.
doi: 10.1016/j.fertnstert.2009.05.009

In this study, the objective was to develop efficient Chinese hamster ovary (CHO) cells that express recombinant human FSH (rhFSH) in serum-free conditions and to investigate the effect of this newly synthesized rhFSH on folliculogenesis and ovulation. A stable single CHO cell that expresses rhFSH at a high level was obtained by introducing the human chorionic gonadotropin (hCG) alpha-subunit and FSH beta-subunit genes. The ability was confirmed of newly synthesized rhFSH obtained from the serum-free culture medium of CHO cells transfected with the common human FSH a- and b-subunit genes on induction of folliculogenesis in hypophysectomized rats and on ovulation in androgen sterilized mice. And the efficacy of newly synthesized rhFSH in folliculogenesis and ovulation induction was equal to commercially available rhFSH (Gonal-F). 

The cells were cultured in serum-free a-MEM (0.25 mmol/L MTX) as specified in the Materials and Methods, under the heading; Expression and Purification of rhFSH in CHO Cells.