PARENT SESSION
COMPARATIVE ASPECTS OF REPRODUCTION
Harborside C
7:30 AM-10:00 AM

(395) A FETAL INFLUENCE ON RELAXIN GENE EXPRESSION IN THE CORPUS LUTEUM OF THE TAMMAR WALLABY.

Parry, Laura^1,2, Gehring, Helen^1,2, ¹ Howard Florey Institute, Parkville, Victoria, Australia² Department of Zoology, Parkville, Victoria, Australia

ABSTRACT- In the tammar wallaby, the lifespan of the corpus luteum (CL) is not extended by the presence of a conceptus and the luteal phase in unmated animals is similar in duration to the 26-day gestation. Moreover, the oestrous cycle is not interrupted by pregnancy. Regardless of whether or not the animal is pregnant, there is a CL on one ovary, whereas the other ovary has a developing follicle throughout the luteal phase. The important difference between the two reproductive cycles is the absence of a conceptus in the nonpregnant cycle. The peptide hormone relaxin (RLX) is synthesized in the tammar CL from day 6 of gestation until term but its expression in unmated animals is not known. The aim of this study was to measure RLX mRNA levels in the CL of pregnant and unmated tammar wallabies to determine if the conceptus influences RLX gene expression. Tissues were obtained from 5 equivalent stages of the pregnant and nonpregnant cycle (n=4 per stage). Real time PCR with tammar specific RLX primers and a FAM-labelled probe in an ABI PRISM 7700 Sequence Detector was used to quantify RLX mRNA levels. Relaxin gene expression was significantly (P<0.01: ANOVA) upregulated in the CL of both pregnant and unmated tammars on day 10 of each cycle. In pregnant animals, RLX mRNA levels remained high until day 26, one day before expected births. In contrast, RLX mRNA levels in unmated animals decreased from day 18, and were significantly (P<0.05) lower compared with pregnant animals at all remaining stages of the nonpregnant cycle. As the yolk placenta forms between days 18-19 in pregnant animals, it is likely that a placental factor is influencing RLX gene expression. Interestingly, removal of the conceptus on day 20 gestation did not significantly affect RLX mRNA levels compared with sham operated controls, which suggests that the critical signalling phase is between days 18-20 gestation. Our data show that the onset of ovarian RLX gene expression is not dependent on the presence of a conceptus but that a placental factor may be important for maintenance of RLX synthesis.

KEY WORDS: relaxin, corpus luteum, fetectomy, marsupial