FOXL2 is inhibited by progesterone in ruminant endometrium

In mammals, implantation îs critical for the outcome of pregnancy and involves tightly regulated and coordinated interactions between the endometrium and the conceptus (embryo and associated extra-embryonic membranes). The mutual actions of estrogen and progesterone on their uterine receptors are essential for the endometrium receptivity and conceptus implantation. Using bovine endometrium at 20 days post-oestrus (dpo), our microarrays analyses have listed the expression offamilies of transcription factors, including severa!members of the winged-helix/forkhead domain (FOX) transcription factors family. We recently demonstrated that FOXL2 -a member of the FOXL sub­ class considered as a key gene for ovarian differentiation- was regulated during early pregnancy in bovine endometrium, independently of the presence of interferon-tau. In the present study, we have aimed to investigate the contribution of steroids hormones in the regulation of FOXL2 gene expression in mminants using physiological and experimental models derived in cattle and sheep. First, we have confirmed tl1at FOXL2 is expressed in the ovine endometrium across the estrans cycle, starting from day 4 to day 15 post-oestrus (dpo) and in pregnancy, at day 15 post­ oestrus (day of implantation in ewe). fn keeping with our data in the bovine endometrium, FOXL2 endometrial expression in sheep is low and similar during the luteal phase of estrous cycle (day 4 to 12 post-oestnls) white its expression (RNA and protein) significantly increases during the luteolytic phase (day 15 post oestrns in cycle). In pregnant ewcs, inhibition of progesterone production (P4) by trilostane (an inhibitor of 3p-hydroxysteroid dehydrogenase activity) during the 5 16 dpo period prevents the P4 rise and leads to a significant increase of FOXL2 transcript expression compared to the control group (1.4-fold in the canmcular area, P < 0.05). Ovariectomized ewes or cows treated with exogenous P4 for 12 days or 6 days respectively have exhibited a significant inhibition ofFOXL2 gene expression compared to control ovariectomized females (in sheep, transcript: 1.8-fold, P < 0.05; protein: 2.4-fold, P < 0.05; in cattle, transcript: 2.2-fold, P < 0.05). Nevertheless, exogenous 17B-estradiol (E2) treatment for 12 days in sheep or 2 days in cattle did not affect FOXL2 endometrial expression compared to control ovariectomized females. In vitro expcriments based on the transient transfection of bovine FOXL2 promoter are unden.vay in arder to confirm the direct impact of P4 and/or E2 treatments on the activity of FOXL2 promoter. Collectively, our results demonstratc that FOXL2 gene expression is down regulated by progesterone in ruminant endometrium. Determining the biological actions of FOXL2 will be necessary to define the contribution of this transcription factor in the sensor and driver properties of the endometrium.