The steroid progesterone induces the resumption of maturation in oocytes via a nongenomic pathway through binding to a novel membrane progestin receptor (mPR). This pathway inhibits adenylyl cyclase and reduces intracellular cAMP, and also activates mitogen-activated protein kinase to effect signal transduction pathways. Five distinct groups, designated Alpha, Beta, Gamma, Delta, comprise the mPR gene family. mPR Alpha, also designated progestin and adipo Theta receptor family member VII (PAQR7), consists of an extracellular N-terminus, an intracellular C-terminus and seven transmembrane domains. mPR Alpha is expressed in ovary, testis, placenta, uterus and bladder. mPR Beta, or progestin and adipo Theta receptor family member VIII (PAQR8), consists of eight putative transmembrane regions and an intracellular N-terminus that contains a leucine-rich motif. mPR Beta is a 354 amino acid protein expressed in brain and spinal cord. Both mPR Alpha and mPR Beta may be G protein-coupled receptors and may be involved in oocyte maturation.