Differential effects of activin-A and FSH on growth, viability and messenger RNA expression in cultured bovine preantral follicles

This study evaluated the effect of follicle stimulating hormone (FSH) alone or in combination with activin-A on survival, growth and expression of mRNA for follicle stimulating hormone receptor (FSH-R), proliferating cell nuclear antigen (PCNA), activin receptor type I B (ActR-IB), activin receptor type II B (ActR-IIB), hyaluronan synthase-1 (HAS 1) and hyaluronan synthase-2 (HAS 2) in bovine secondary follicles cultured in vitro for 18 days. Preantral follicles (~0.2 mm) were isolated and individually cultured in absence (α-minimum essential medium (α-MEM+): control) or presence of activin-A, FSH in increasing concentrations or both activin-A and FSH. An increase in follicular diameter was observed after 6 days of culture in all culture treatments compared to control medium; after 12 days in treatment with FSH alone or the mixture of FSH and activin-A (P<0.05); and, after 18 days only in the presence of FSH alone (P<0.05). However, in combination with activin-A, FSH-stimulated follicle growth after 18 days was blocked (P<0.05) and, had significantly lower (P<0.05) levels of mRNA for ActR-IB, ActR-IIB, when compared to α-MEM+, and for FSH-R and PCNA, when compared to α-MEM+ supplemented with activin-A only. Moreover, follicles cultured in presence of FSH alone had greater (P<0.05) levels of mRNA for HAS 1 and HAS 2 than those cultured in medium supplemented with both activin-A and FSH. Morphological, immunofluorescence and ultrastructural analysis confirmed the integrity of follicles cultured in FSH after 18 days. In conclusion, activin-A exerts a stimulatory effect on in vitro early follicular development for up to 6 days, has no effect after 12 days of culture and blocks the stimulatory growth effect of FSH after 18 days. The reduced mRNA levels in follicles cultured with both activin-A and FSH suggest a decreased sensitivity of follicles for activin-A and FSH and inhibited follicular cell proliferation after long-term in vitro culture of isolated preantral follicles.