Prematuration of bovine oocytes with butyrolactone I reversibly arrests meiosis without increasing meiotic abnormalities after in vitro maturation in live and fixed oocytes.

1Elisa M. Ferreira, 1Alessandra A. Vireque, 2Paulo Adona, 1Rui A. Ferriani, 1Marcos F. Silva de Sá, 1Paula A.A.S. Navarro.
1Department of Obstetrics and Gynecology, Ribeirão Preto Medical School, University of São Paulo, Ribeirão Preto, São Paulo, Brazil; 2Department of Basic Sciences, Faculty of Zootechny and Aliments Engeneering, University of São Paulo, Pirassununga, São Paulo, Brazil.

Objective: To investigate the effect of prematuration with the nuclear maturation inhibitor butyrolactone I (BLI) on the meiotic spindle and chromosomal configuration of live and fixed bovine oocytes.

Methods: A morphological study using bovine oocytes submitted to in vitro maturation (IVM) after pretreatment with BLI was performed. Immature oocytes obtained from slaughtered cows were divided into three groups: control, submitted to IVM for 24 h; BLI 18 h, prematured with BLI for 24 followed by 18 h of IVM; and BLI 24 h, prematured with BLI for 24 h followed by 24 h of IVM. Meiotic anomalies were assessed using imunofluorescence microscopy and polarization imaging (Polscope) (OCTAX ICSI GuardTM System, Altdorf, Germany).

Results: Meiotic arrest occurred in 88.8% of the oocytes cultured with BLI. Maturation rates were similar for all groups as analyzed by polarization and immunofluorescence microscopy. There were no differences among control, BLI 18h and BLI 24h groups with respect to the percentage of meiotic spindle visualization by polscope (51%; 41% e 51.1%, respectively). The incidence of meiotic anomalies did not differ between groups (17%, 19%, and 16.9% for the control, BLI 18h and BLI 24h, respectively) according to immunofluorescence microscopy.

Conclusions: Prematuration with butyrolactone I reversibly arrests meiosis without damaging the meiotic spindle or chromosome distribution of bovine oocytes after IVM. Polscope allows visualization of meiotic spindles in approximately 50% of living in vitro matured oocytes prematured with BLI, suggesting this may be a useful tool to identify this important cell structure, with potential different applications.