Kinase pathways in dominant and subordinate ovarian follicles during the first wave of follicular development in sheep

The mechanism by which one or more dominant ovarian follicles continue deve lopment while other subordinate follicles regress is not known. The mitogen activated protein kinases (MAPKs) are a group of kinases that are activate d by hormonal factors and form a cascade of processes that regulate cell gr owth, division and differentiation. The aim of the present experiment was t o characterise the presence of the MAPKs, Erk 1/Erk 2 and Akt in healthy do minant follicles and regressing subordinate follicles. Following in vivo mo nitoring of ovarian follicle development, three ewes were ovariectomised an d the follicular fluid and follicle wail (theca and granulosa cells) saved from the dominant and largest subordinate follicle. The dissected diameter and follicular fluid oestradiol concentration of the the dominant follicle was larger (P < 0.01) than the largest subordinate follicle (6.5 +/- 0.0 mm and 41.3 +/- 4.9 ng/ml versus 4.7 +/- 0.3 mm and 0.6 +/- 0.4 ng/ml). Weste rn blot analyses showed that there was more Akt (202.7 +/- 6.4 versus 59.6 +/- 32.7 units; P < 0.05) and Erk 1/Erk 2 (104.5 +/- 10.6 versus 0.3 +/- 0. 2 units; P < 0.01) present in follicle wall samples from the dominant compa red to the largest subordinate follicles. Phosphorylated forms of Akt and E rk 1/Erk 2 were detected in samples from dominant but not subordinate folli cles. We suggest that signal transduction pathways involving Akt and Erk 1/ Erk 2 may play an important role in determining the outcome of ovarian foll icle growth and development in sheep. (C) 2000 Elsevier Science B.V. All ri ghts reserved.