Figure 1.

Follistatin-like 3 (FSTL3) is important in limiting testicular size and inducing testicular regression in mice. Photographs showing enlarged testes in Fstl3^−/− (FSTL3 knockout [KO]) compared to wild-type (WT) mice at 3 mo (A) and 10 mo (B), respectively. Bar graphs showing epididymal sperm counts from 6-mo-old WT (n = 10) and FSTL3 KO (n = 10) mice (C); serum testosterone levels from age-matched WT (n = 10) and KO (n = 22) animals (D); interlitter interval in days (d) (E) and litter size (F) in WT and KO mating pairs (n = 4 pairs, 3-4 litters). Graph of paired testes weights plotted against mean age of WT and FSTL3 KO mice (G). Testes were significantly larger in KO mice than WT mice at all ages measured. Although WT mice show a decrease in testicular weight with age, such regression is not seen in the FSTL3 KO mice. Error bars = SEM; a, b, *P < .05; c, ** P < .01; *** P < 10⁻⁵.