Cumulus-oocyte complexes in vitro maturation from Holstein cows with pregnancy-associated plasm protein-A: effects on embryo production and quality

Abstract

Growth factors are widely studied in the composition of the maturation medium, including, the like growth factor similar to insulin (IGF), as predicted as positive in embryonic development and oocyte maturation in vivo and in vitro. The IGF bioactivity is regulated by two mechanisms: IGFBPs (IGF binding-proteins) and PAPPA (Pregnancy-associated serum protein-A), the second being able to cleave IGF linked to the IGFBPs, increasing the bioavailability of free IGF. Recent studies have demonstrated the differential expression of members of this system in immature oocytes or embryos produced in vitro comparing Nelore females (Bos taurus indicus) and Holstein (Bos taurus taurus). In this sense, deserves the highest expression of PAPPA found in immature oocytes from Nelore cows, which could imply in better ability in the bioavailability of IGF-1 by these oocytes derived females and positively impact on embryo production in vitro. A lot of studies have investigated the effects of adding IGF-1 exogenous to the maturation medium, however, recent data obtained by our group demonstrated the positive effect of the addition of PAPPA during IVM slaughterhouse oocytes (mostly Bos taurus indicus females) on meiotic progression and an increase in the expression of quality reference genes in vitro produced embryos. If such modulation is already showing positive effects in slaughterhouse ovaries, hypothesize that this effect is more evident in cow oocytes Holstein, improving the rate and quality of embryos. The aim of this study is to investigate the effects of adding the PAPPA during IVM of cow oocytes Holstein on oocyte production and quality embryo. For this complex cumulus-oocyte (COCs) bovine from ovum pick up (OPU) of Holstein cow ovaries will be matured or not with PAPPA (0 and 100 ng/ml, more effective dosage in previous experiments), and cultured until the blastocyst stage. At D7 (7p day embryo in vitro culture), the rate of production will be checked and blastocysts obtained submitted to relative quantification in embryonic competence genes and differential count of inner cell mass cells (ICM) and trophoectoderm (TE): ICM/ TE ratio. It is expected that the addition of PAPPA during IVM, modulates the bioavailability of IGF and consequently the positive effects of this system reflect a greater oocyte quality, increase production efficiency and embryo quality in Holstein females. (AU)