Downregulation of nuclear progestin receptor (Pgr) and subfertility in double knockouts of progestin receptor membrane component 1 (pgrmc1) and pgrmc2 in zebrafish.

The progestin receptor membrane components (Pgrmcs) contain two paralogs, Pgrmc1 and Pgrmc2. Our previous research into single knockout of Pgrmc1 or Pgrmc2 suggests that Pgrmc1 and Pgrmc2 regulate membrane progestin receptor or steroid synthesis and therefore female fertility in zebrafish. Additional roles of Pgrmcs may not be determined in using single Pgrmc knockouts due to compensatory roles between Pgrmc1 and Pgrmc2. To address this question, we crossed single knockout pgrmc1 (pgrmc1-/-) with pgrmc2 (pgrmc2-/-), and generated double knockouts for both pgrmc1 and pgrmc2 (pgrmc1/2-/-) in a vertebrate model, zebrafish. In addition to the delayed oocyte maturation and reduced female fertility, significant reduced ovulation was found in double knockout (pgrmc1/2-/-) in vivo, though not detected in either single knockout of Pgrmc (pgrmc1-/- or pgrmc2-/-). We also found significant down regulation of nuclear progestin receptor (Pgr) protein expression only in pgrmc1/2-/-, which was most likely the cause of reduced ovulation. Lower protein expression of Pgr also resulted in reduced expression of metalloproteinase in pgrmc1/2-/-. With this study, we have provided new evidence for the physiological functions of Pgrmcs in the regulation of female fertility by regulation of ovulation, likely via regulation of Pgr, which affects regulation of metalloproteinase expression and oocyte ovulation.