Expression of high density lipoprotein-binding protein messenger ribonucleic acid in the rat ovary and its regulation by gonadotropin.

The presence of high density lipoprotein-binding protein (HBP) mRNA in rat ovarian cells and its possible regulation by gonadotropin were examined in this study. RNA, isolated from pseudopregnant rat ovaries, was amplified by reverse transcriptase-polymerase chain reaction (PCR) with HBP-specific oligonucleotide primers. A distinct and prominent 576-basepair PCR product was generated. Sequence analysis revealed that the sequence homology of the PCR product and the corresponding human HBP cDNA sequence was greater than 90%. Using Northern blot analysis, we identified two species of HBP mRNA transcripts in the ovarian cells (i.e. a major one of 4.5 kilobases and a minor one of 6.0 kilobases). Cellular localization of HBP mRNA in the ovary was determined by in situ hybridization analysis. Prominent specific hybridization of the labeled antisense probe was observed in all cell types of the follicles and corpora lutea, whereas little hybridization was observed in the stroma and the connective tissues separating corpora lutea and follicles. As hCG has been shown to induce high density lipoprotein-binding activity in the rat ovary, we examined the possible regulation of ovarian HBP mRNA by this hormone. Administration of hCG caused a significant time-dependent increase in the steady state levels of HBP mRNA. The induction of HBP mRNA levels by hCG is specific for the ovary, as pretreatment with hCG had no effect on the HBP mRNA levels of the liver, heart, lung, or kidney. The present study, for the first time, shows conclusively the presence of HBP mRNA in the rat ovary and its induction by hCG, implicating a physiological role for HBP in the ovary.