Small Size Hyluronan Promotes Bovine Oocyte Maturation and Embryo Development In Vitro.

Abstract

The ability of the oocyte to develop to the blastocyst stage following in vitro fertilisation and subsequently a good quality embryo is affected by the microenvironment in which it is cultured. Hyaluronic acid (HA) is an important component of the extracellular matrix which is important for cumulus cells expansion and is present in the follicular oviductal and uterine fluids and is expressed in bovine oocytes and embryos. Hyaluronidase (Hyal) is an enzyme present in the oviduct and uterus and cleaves the HA into biologically active small fragments, facilitating its uptake or degradation. Bovine oocytes or cleaved embryos were matured in vitro in the presence or absence of HA, Hyal-2 or 4-Methylumbelliferone (4-MU), a HA synthesis inhibitor. The rates of oocyte nuclear maturation to the metaphase II stage and development of embryos to blastocyst stage and blastocyst quality were recorded. Large size HA and also Hyal-2 inhibited cumulus cells expansion without affecting oocyte maturation. 4-Mu at 1mM reduced cumulus cells expansion and oocytes maturation rate. Supplementation of embryo culture media with 300 Units/ml Hyal-2 significantly improved the blastocysts yield, and quality by increasing the total cell number and number of cells in the Inner Cell Mass (ICM). Fewer blastocysts were produced when 4-MU was added to the culture medium (P < 0.01). This data suggests that intrinsic HA production is critical for oocyte maturation and blastocyst development and also has an effect on embryo quality. This study therefore provides evidence for critical role of small HA fragments on improving embryo quality and development. (poster)