Embryo

Developmental Regulation of Hyaluronan-Binding Protein (RHAMM/IHABP) Expression in Early Bovine Embryos

Abstract

Hyaluronan or hyaluronic acid (HA) is a normal component of mammalian follicular, oviduct and uterine fluids. Granulosa and expanding cumulus cells secrete large amounts of HA, and added in maturation and culture media HA improved developmental potential of oocytes and embryos. HA regulates gene expression, signaling, proliferation, motility, adhesion, and morphogenesis. Many of these biological activities of HA are mediated through binding to receptor for hyaluronic acid mediated motility/intracellular HA-binding protein (RHAMM/IHABP). We evaluated the presence and dynamics of RHAMM/IHABP mRNA and protein expression in different stages of in vitro produced bovine embryos using quantitative RT-real time-PCR and immunohistochemistry. Additionally, we analyzed the effects of different culture systems on the relative abundance of RHAMM/IHABP transcripts. RHAMM/IHABP mRNA levels decreased from the 2-cell to the 16-cell stage, increasing again at morula stage, reaching the highest level at expanded blastocyst stage. RHAMM/IHABP mRNA abundance was significantly (P < 0.05) lower in embryos recovered in serum-containing medium than in embryos from serum-free media. Immunohistochemistry revealed presence of RHAMM/IHABP first in 8-cell stages. Whereas the RHAMM staining in 8-cell and morula stages was very intensive, it was weaker in blastocysts. Embryonic secretion of HA increased from 2-cell stage until 8-cell stage and then decreased in 16-cell embryo. After this, secretion of HA increased in expanded and hatched blastocyst stages. These data suggest that the positive effects of HA on in vitro produced bovine embryos may, at least in part, be mediated by RHAMM/IHABP.