Dehydrogenase/D5-D4 Isomerase: Molecular Cloning and Regulation of Their Messenger Ribonucleic Acids in Equine Follicles During the Ovulatory Process1

The preovulatory LH rise is the physiological trigger of follic-ular luteinization, a process during which the synthesis of pro-gesterone is markedly increased. To study the control of follic-ular progesterone biosynthesis in mares, the objectives of this study were to clone and characterize the equine cholesterol side-chain cleavage cytochrome P450 (P450scc) and 3b-hydroxy-steroid dehydrogenase/D5-D4-isomerase (3b-HSD), and describe the regulation and cellular localization of their transcripts in equine follicles during hCG-induced ovulation. Complementary DNA cloning and primer extension analyses revealed that the equine P450scc transcript is composed of a 59-untranslated re-gion (UTR) of 52 nucleotides, an open reading frame (ORF) of 1560 nucleotides, and a 39-UTR of 225 nucleotides, whereas the equine 3b-HSD mRNA consists of a 59-UTR of 61 nucleotides, an ORF of 1119 nucleotides, and a 39-UTR of 432 nucleotides. The equine P450scc and 3b-HSD ORF encode 520 and 373 ami-no acid proteins, respectively, that are highly conserved (68– 79 % identity) when compared to homologs of other mammalian species. Northern blot analyses were performed with preovu