Fibroblast growth factor-16 is a growth factor for embryonic brown adipocytes

In rat embryos, fibroblast growth factor (FGF)-16 is predominantly expresse d in brown adipose tissue. To elucidate the role of FGF-16, we examined the expression of FGF-16 mRNA in rat embryonic brown adipose tissue at differe nt developmental stages by Northern blotting analysis and in situ hybridiza tion. FGF-16 mRNA was expressed abundantly in brown adipose tissue during e mbryonic day 17.5, embryonic days 17.5-19.5, and thereafter at lower levels into the neonatal period. The expression profile of FGF-16 mRNA well corre sponds to the proliferative profile of embryonic brown adipose tissue repor ted. We also examined the mitogenic activity of recombinant rat FGF-16 for primary brown adipocytes prepared from rat embryonic brown adipose tissue. FGF-16 showed significant mitogenic activity for primary brown adipocytes. The mitogenic activity was found to be exerted by binding and activating FG F receptor-4 in the brown adipose tissue. As a great induction of prolifera tion of rat brown adipose tissue during cold acclimation was reported, we a lso examined the expression of FGF-16 mRNA in the brown adipose tissue duri ng cold acclimation by Northern blotting analysis. The expression of FGF-16 mRNA was not increased, but rather decreased. The expression profile of FG F-16 mRNA and the mitogenic activity of FGF-16 reported here indicate that FGF-16 is a unique growth factor involved in proliferation of embryonic bro wn adipose tissue.