Association between three glycosidases activity A - mannosidase ( A-ΜΑΝ ), B-Ν-acetyloglucosaminidase (NAGASE) and B - galactosidase (B-GAL) andin vitro fertilization of bovine oocytes collected from different-sized follicles

ABSTRACT

We studied the role of three glycosidases (α-mannosidase - α-ΜΑΝ, β-N-acetyloglucosaminidase -NAGASE and β-galactosidase - β-GAL) in follicularfluid (FF) and in fertilization medium (FM) of bovineoocytes. Oocytes were allocated into 3 groups accordingto the follicular size (controls - CF 2-8 mm, smallfollicle group - SF 2-5 mm, large follicle group - LF>5-8 mm). Bovine embryos were produced in vitroeither in groups (experiment 1, n = 2099 oocytes) orindividually (experiment 2, n = 79 oocytes). In bothexperiments, the activity of all glycosidases in the FF oflarge follicles was significantly lower than in the FF ofsmall follicles group. In the FM of LF-group oocytes, α-MAN and NAGASE were significantly higher comparedto SF- and CF-group oocytes (experiment 1) and β-GALwas significantly higher in SF- compared to CF-groupoocytes (experiment 2). Cleavage rate was similar amongall groups in both experiments; however significantlyhigher blastocyst formation was noted in CF-groupcompared to LF- (days 7, 8, 9) and SF- (days 8, 9) groups(experiment 1). In follicular fluid of small follicle group,β-GAL was associated positively with degeneratingoocytes’ number and negatively with blastocyst rate atdays 7, 8 (P = 0.065) and 9 (experiment 1). In fertilizationmedium of control group, α-MAN related negatively tocleavage rate (P < 0.05) and β-GAL to blastocyst rate atday 8 (P = 0.089) or day 9 (P = 0.072) (experiment 1).During fertilization, in experiment 1 all oocytesconsumed β-GAL and only control or small follicleoocytes consumed α-MAN; in experiment 1, only largefollicle oocytes released NAGASE, whereas all oocytesreleased all three glycosidases in experiment 2. Inconclusion, glycosidases affect the developmentalcompetence of oocytes collected from different sizedfollicles during in vitro fertilization, performed either ingroups or individually; their role in follicular fluid isdifferent from that in fertilization medium.