Zygote: page 1 of 13 c  Cambridge University Press 2018 doi:10.1017/S0967199418000102 Urea changes oocyte competence and gene expression in resultant bovine embryo in vitro Rasoul Kowsar 1, 3 , Fatemeh Izadi 2 , Nima Sadeghi 4 , Ahmad Riasi 2 , Faezeh Ghazvini Zadegan 5 , Mehdi Hajian 5 , Mohammad Hossein Nasr-Esfahani 1, 6 , Hossein Farrokhpour 7 and Akio Miyamoto 3 College of Agriculture, Isfahan University of Technology, Isfahan, Iran; Obihiro University of Agriculture and Veterinary Medicine, Obihiro, Hokkaido, Japan; FKA, Animal Husbandry and Agriculture Co., Isfahan, Iran; Reproductive Biomedicine Research Center, Royan Institute for Biotechnology, ACECR, Isfahan, Iran; and Department of Chemistry, Isfahan University of Technology, Isfahan, Iran Date submitted: 17.10.2017. Date revised: 28.03.2018. Date accepted: 01.04.2018 Summary Nutrition infuences the microenvironment in the proximity of oocyte and affects early embryonic development. Elevated blood urea nitrogen, even in healthy dairy cows, is associated with reduced fertility and there is high correlation between blood urea levels and follicular fuid urea levels. Using a docking calculation (in silico), urea showed a favorable binding activity towards the ZP-N domain of ZP3, that of ZP2, and towards the predicted full-length sperm receptor ZP3. Supplementation of oocyte maturation medium with nutrition-related levels of urea (20 or 40 mg/dl as seen in healthy dairy cows fed on low or high dietary protein, respectively) dose-dependently increased: (i) the proportion of oocytes that remained uncleaved; and (ii) oocyte degeneration; and reduced cleavage, blastocyst and hatching rates. High levels of urea induced shrinkage in oocytes, visualised using scanning electron microscopy. Urea downregulated NANOG while dose-dependently upregulating OCT4, DNMT1, and BCL2 expression. Urea at 20 mg/dl induced BAX expression. Using mathematical modelling, the rate of oocyte degeneration was sensitive to urea levels; while cleavage, blastocyst and hatching rates exhibited negative sensitivity. The present data imply a novel role for urea in reducing oocyte competence and changing gene expression in the resultant embryos. Keywords: Blastocyst, Bovine oocyte, Molecular docking, Urea 1 All correspondence to: Rasoul Kowsar. Department of Animal Science, College of Agriculture, Isfahan University of Technology, Isfahan,84156-83111, Iran. E-mail: Rasoul_kowsarzar@yahoo.com or Mohammad Hossein Nasr-Esfahani. Department of Reproductive Biotechnology, Reproductive Biomedicine Research Center, Royan Institute for Biotechnology, ACECR, Isfahan, Iran. E-mail: mh.nasr- esfahani@royaninstitute.org 2 Department of Animal Science, College of Agriculture, Isfahan University of Technology, Isfahan, 84156-83111, Iran 3 Graduate School of Animal and Food Hygiene, Obihiro University of Agriculture and Veterinary Medicine, Obihiro, Hokkaido 080–8555, Japan 4 FKA, Animal Husbandry and Agriculture Co, Isfahan, Iran 5 Department of Reproductive Biotechnology, Reproductive Biomedicine Research Center, Royan Institute for Biotechnology, ACECR, Isfahan, Iran Introduction The chemical composition of follicular fuid plays an important role in oocyte fertilizability and also in the resultant embryo development because developing oo- cytes are in direct proximity to this microenvironment (Fortune, 1994; Józwik et al., 2006; Revelli et al., 2009). Urea can be transported by passive diffusion through the blood–follicle barrier (Józwik et al., 2006), indicating a substantial correlation between urea concentration in follicular fuid and plasma in both humans and 6 Department of Embryology, Reproductive Biomedicine Research Center, Royan Institute for Reproductive Biomedicine, ACECR, Tehran, Iran 7 Department of Chemistry, Isfahan University of Technology, Isfahan, 84156-83111, Iran.