Sequence variation and evaluation of inhibin alpha-subunit and steroidogenic acute regulatory protein for reproductive traits in swine.

Source/description: Ovulation rate is an important trait influencing litter size in swine and contributes to reproductive success in pig production. Several quantitative trait loci (QTL) for ovulation rate have been identified in the pig. One region on chromosome 15 was associated with ovulation rate in a Meishan cross and in lines selected for components of litter size. The porcine inhibin a-subunit (INHA) and steroidogenic acute regulatory protein (STAR) genes were previously mapped to this region by polymerase chain reaction-restriction fragment length polymorphism. Inhibin a-subunit is a gonadal glycoprotein that binds to the inhibin bA and bB subunits to form heterodimer complexes known as inhibin A or inhibin B respectively; it also regulates the secretion of pituitary follicle stimulating hormone (FSH). Plasma inhibin is correlated with higher ovulation rates in pigs. The transportation of cholesterol from the outer to the inner mitochondrial membrane is the rate-limiting step for steroidogenesis, is conducted by STAR in testis, ovary and adrenal and is regulated by FSH and insulinlike growth factor 1 (IGF1). Therefore, we considered INHA and STAR as positional candidates for this QTL and evaluated their sequence for potential causative genetic variation.