PARENT SESSION
BIOLOGY OF THE FEMALE REPRODUCTIVE TRACT
Harborside C
7:30 AM-10:00 AM

(538) TEMPORAL AND SPATIAL REGULATION OF ESTROGEN RECEPTOR (ER) AND PROGESTERONE RECEPTOR (PR) EXPRESSION IN THE ENDOMETRIUM OF NONPREGNANT AND EARLY PREGNANT MARES.

Hartt, Leslie¹, Joyce, Margaret¹, Sinor, Stacy¹, Liu, Hongzhi¹, Johnson, Greg¹, Vanderwall, Dirk¹, Ott, Troy¹, ¹ Department of Animal and Veterinary Science, Moscow, Idaho

ABSTRACT- ER and PR are nuclear transcription factors that mediate cellular functions of estrogen and progesterone in the uterus during the estrous cycle and pregnancy. Temporal and spatial distribution of ER and PR in the uterine endometrium during the cycle and early pregnancy remains poorly characterized in the mare. The present study examined the temporal and spatial distribution of ER and PR mRNA in the endometrium of nonpregnant and pregnant mares. Endometrial biopsies were taken on days (D) 0 (ovulation), and 8 from nonmated mares and on D 11, 14, 17, and 20 from nonmated and pregnant mares (n = 4-6 mares/day/status). Tissues were either fixed and embedded in paraffin or subjected to total RNA extraction. Slot-blot analysis was used to quantify steady-state levels of ER and PR mRNA in the endometrium. Steady-state levels of ER and PR were highest on D 0, 17 and 20 in nonpregnant mares and lowest on D 11 and 14 (p<0.01). In contrast, on D 17 and 20 pregnant mares exhibited low levels of ER and PR compared to corresponding days of the cycle (p<0.01). In situ hybridization analysis was consistent with results from slot-blots. In nonpregnant mares, high levels of ER mRNA were detected throughout the endometrium on D 0 and 20, with highest expression in the glandular (GE) and luminal epithelium (LE). In pregnant mares, ER mRNA remained at a constant low level in GE, with some mares demonstrating relatively higher expression in the deep GE than in the shallow GE on D 11 and 14. Differences in level of expression of ER were detected on D 17 and 20 between pregnant and nonpregnant mares. PR expression throughout the endometrium was low during the cycle with highest expression in GE on D 0 and 20. PR expression was suppressed in all cell types at D20 of pregnancy compared to D 20 of the cycle. Results are consistent with the temporal and spatial regulation of ER and PR in other domestic farm species; namely pregnancy suppresses the cyclic increases of ER and PR expression in the uterine endometrium. These results offer a framework for further investigation of steroid receptor regulation in establishment and maintenance of pregnancy in the mare.

KEY WORDS: horse, uterus , estrogen receptor, progesterone receptor