Temporal gene expression in equine corpora lutea based on serial biopsies in vivo1

A biopsy procedure was developed to enable repeated sampling of a single equine corpus luteum (CL) over the course of an estrous cycle. The tissue collected was utilized in characterizing mRNA levels for genes involved in luteal formation, function, and regression in the cyclic mare. Serial biopsies of CL in cyclic mares (2.7 to 27.5 mg per biopsy) were collected using an ultrasound-guided transvaginal technique. Biopsies were collected from each mare on d 2 and 5 (d 0 = ovulation) of the estrous cycle, and every other day from d 12 through luteolysis. Samples were obtained from 4 mares with normal estrous cycles and 1 mare with a retained CL. The biopsy procedure did not adversely affect luteal size or function, as measured by luteal area and serum concentrations of progesterone. Real time RT-PCR was used to quantify steady state mRNA concentrations in each tissue sample obtained. Mean levels of steroidogenic acute regulatory protein (StAR) mRNA were not different on any of the sampling dates, but a trend for mRNA encoding StAR to decrease between d 12 and 14 (P = 0.10) was observed. Values for mRNA encoding StAR were positively correlated to serum concentrations of progesterone on d 5 (R = 0.95; P = 0.05) and 14 (R > 0.99; P < 0.01). Steady state levels of mRNA for 3β-hydroxysteroid dehydrogenase, Δ 5-Δ 4 isomerase (3β-HSD) declined between d 12 and 14 (P = 0.15). There were positive correlations between mRNA for 3β-HSD and concentrations of progesterone on d 5 (R = 0.94; P = 0.06) and 12 (R > 0.99; P = 0.05). No difference was detected in levels of mRNA encoding cyclooxygenase-2 (cox-2) or caspase-3 between any of the sampling dates. A successful luteal biopsy procedure was developed that did not negatively affect luteal function, and levels of mRNA encoding StAR, 3β-HSD, cox-2 and caspase-3 were characterized in luteal biopsy tissue collected on d 2, 5, 12, and 14 of the estrous cycle in the mare. [PUBLICATION ABSTRACT]