PARENT SESSION
Corpus Luteum

DYNAMIC EXPRESSION AND SELECTIVE LOCALIZATION OF mRNA ENCODING THE PGF₂ RECEPTOR IN THE PORCINE CORPUS LUTEUM DURING THE ESTROUS CYCLE.

Boonyaprakob, Ukadej¹, Gadsby, John ², Hedgpeth, Vickie², Routh, Patty¹, Almond, Glen¹, ^{1 2}

ABSTRACT- In the pig, prostaglandin (PG)F₂ mediates regression of the corpus luteum (CL) by means of specific plasma membrane associated PGF₂ (FP) receptors. Changes in the expression and localization of luteal mRNA for this receptor may be critical in determining the luteolytic action of PGF₂. To investigate the expression and cellular localization of mRNA encoding the FP receptor in the porcine CL, a partial cDNA was produced by reverse transcription polymerase chain reaction (RTPCR). This 283-bp cDNA was 92% identical to that of the human FP receptor mRNA. CLs were collected from cycling gilts on days 4, 7, 10, 13 and 15 of the estrous cycle (day 0 = estrus; n = 4 - 5 animals per day). One to two CLs were collected from each animal, embedded in OCT media and frozen at -80°C. The remaining CLs were dissociated and mixed luteal cells were centrifuged on to slides (cytospin) to obtain 20,000 large cells per slide and stored at -80°C. The sections of the frozen CLs (8m) and cytospin slides were subjected to in situ hybridization analysis with ³⁵S labeled riboprobes specific to the porcine FP receptor, and the intensities of the sections for this receptor were quantified using phosphorimage analysis. The results indicated a relatively weak signal on day 4 (9.60 ± 0.44 arbitrary units), day 7 (7.64 ± 0.90) and day 10 (11.38 ± 2.29), respectively, but an approximately two-fold increased on day 13 (22.05 ± 3.87, p<0.05 vs Days 4-10). On day 15, the variation (15.03 ± 4.66) in the expression of FP receptor mRNA was high and thus, day 15 did not differ from other days. In addition, we showed that mRNA for FP receptor was expressed predominantly on the steroidogenic large luteal cell sub-type, although there was some expression of the FP receptor mRNA on small luteal cells. Although the exact small luteal cell type involved cannot be defined at this time, it appears histologically to be the steroidogenic small cell sub-type. Collectively, these data confirm previous receptor binding studies and provide evidence for the expression of FP receptor mRNA during the luteal phase in the pig. (Supported by The Fund for Discovery program, CVM, NCSU)

KEY WORDS: corpus luteum