CHORIONIC-GONADOTROPIN ALPHA-SUBUNIT AND BETA-SUBUNIT RNAS ARE PRESENT IN EQUINE PLACENTAL MEMBRANES BY DAY 30 OF PREGNANCY

Northern analysis was used to investigate timing of transcription of t he genes for alpha and beta subunits of chorionic gonadotropin (CG) by equine conceptuses. Two conceptuses were collected on each of days 26 , 28, 30 and 32 after ovulation. Conceptus membranes and embryos were separated and frozen immediately on dry ice. Total RNA was extracted, electrophoretically separated on agarose gels, and RNA was transferred to nitrocellulose membranes by osmotic blotting. Total RNA from equin e liver, pituitary, testis and from a day 32 embryo served as controls . The alpha and beta subunits were both first detected in RNA extracte d from day 30 conceptus membranes. The alpha subunit was detected in p lacental membrane RNA from both samples at day 30 and in both samples at day 32. The beta subunit was detected in RNA in only one sample at day 30 and in both samples at day 32. Both alpha and beta subunits wer e detected in equine pituitary RNA, but neither was detected in embryo , liver or testis RNA. These results indicate that transcription of th e genes for alpha and beta subunits of CG has begun by day 30 of gesta tion. This is well before the chorionic girdle cells invade the endome trium to form endometrial cups, and earlier than has been reported for presence of the hormone in serum or for in vitro production by girdle cells.