Expression of growth and differentiation Factor 9 and cognate receptors during final follicular growth in cattle

ABSTRACT

Mutations in growth and differentiation factor9 (GDF9) gene are associated to sterility or,paradoxically, increased ovulation rate in ewes. Despiteits importance, the exact function of GDF9 in ovarianphysiology is still poorly understood. This study aimedto investigate GDF9 function during dominant folliclegrowth and its regulation in follicular fluid. Theregulation of GDF9 receptors in GnRH/LH-stimulatedgranulosa cells was also investigated. In a firstexperiment, a new follicular wave was induced and theintrafollicular GDF9 treatment into the largest growingfollicle (8.5-9.5 mm) at both 100 (n = 3) and 1000ng/ml(n = 4) had no effect on follicular growth, estrusmanifestation and ovulation compared to control (PBSinjected)follicles (n = 3). In a second experiment,follicles were obtained just after follicular deviation(day 4 after follicular emergence) and the abundance ofGDF9 in follicular fluid did not differ between healthydominant (n = 4) and atretic subordinate follicles (n =4), as assessed by western blot analysis. Finally, mRNAexpression of BMPR2 and TGFBR1 receptors wasevaluated in granulosa cells obtained from preovulatoryfollicles (>12 mm diameter) obtained 0, 3, 6, 12 or 24 hafter i.m. GnRH administration (n = 4-5follicles/moment). Both receptors were significantly upregulated 12 h after GnRH treatment. Present results donot confirm the hypothesis that GDF9 inhibits dominantfollicle growth and suggests a minor role in determiningfollicle fate. In the other hand, GDF9 receptorsregulation in GnRH/LH-stimulated granulosa cellsprovides the first in vivo evidence of its involvement inthe complex cascade of events that culminates inovulation and luteinization in cattle.(AU)