(a) Comparison of steady-state levels of Nppc mRNA in the ampulla, isthmus, uterotubal junction (junction) and ovulated oocyte-cumulus complexes (OCCs) isolated from mice at diestrus or ovulation. The mean value in the uterotubal junction from mice at diestrus was set as 1. Bars indicate the mean ± SEM of three experiments. *P < 0.05; ***P < 0.001. (b) In situ hybridization showing Nppc mRNA expression in epithelium (arrows) of oviductal ampulla. Frozen sections of ampullae were hybridized with DIG-labeled antisense probe detecting Nppc mRNA (left panels), and the sense probe detecting control group (right panels). Sense probes yielded only background staining. Asterisks (*) indicate the cumulus cell. Scale bars, 50 μm. (c) Comparison of NPPC levels in the ampulla, isthmus, and uterotubal junction of mice at ovulation. Bars indicate the mean ± SEM of three experiments. **P < 0.01. (d) Effect of ovulation on Nppc expression in ampulla. Nppc mRNA levels in the ampullae were increased only in the presence of the ovulated OCCs. In the left panel, the mean value of the ampullae isolated at 0 h post hCG was set as 1. Bars indicate the mean ± SEM of three experiments. **P < 0.01. (e) The effects of OCCs, cumulus cells, oocytes and oocyte-derived paracrine factors on Nppc expression in ampullae. Ampullae isolated from preovulatory mice (at 11 h post hCG) were cocultured with OCCs, oocytectomized (OOX) cumulus cells, denuded oocytes (oocyte; three oocytes/μL), or oocyte-derived paracrine factors human GDF9 (500 ng/mL), human BMP15 (500 ng/mL) and human FGF8B (FGF8, 100 ng/mL), or the combination of the three proteins for 3 h and levels of Nppc mRNA were determined. The mean value in the control (no treatment) group was set as 1. Bars indicate the mean ± SEM; n, number of independent replicates. *P < 0.05; **P < 0.01.