Membrane progesterone receptor gamma: tissue distribution and expression in ciliated cells in the fallopian tube

Non-genomic, rapid actions of steroids have long been known, suggesting the possible presence of non-classical steroid receptors. A membrane receptor for progestins (mPR) was recently described in the spotted seatrout, and transcripts of three related receptors (alpha, beta, and gamma) were subsequently identified in other species including human and mouse. To begin exploring the roles of mPRgamma in mammals, we have generated an antibody against this receptor. The specificity of the antibody was demonstrated by both overexpression and RNA interference experiments. Using the antibody, we show that mPRgamma is expressed in female mouse reproductive tissues such as ovary and fallopian tube, and also in the lung and liver of both sexes. Immunohistochemical studies revealed that mPRgamma is associated with the apical membrane of ciliated cells facing the lumen of the fallopian tube. The presence of mPRgamma in ciliated cells of the fallopian tube was also demonstrated in human samples. Rapid effects of progesterone on ciliary beat frequency in the fallopian tube have recently been reported. Together, this suggests a common role for mPRgamma in the regulation of ciliary activity in the fallopian tube and thus gamete transport in mammals. The presence of mPRgamma in lung and liver of mice suggests that the receptor mediates the actions of progesterone outside the reproductive tract as well.