Maturation system affects lipid accumulation in bovine oocytes

This study evaluated the effects of three maturation systems, namely in vitro (MatV) and in vivo (MatS) systems, as well as intrafollicular transfer of immature oocytes (IFIOT; MatT), on the accumulation of lipid droplets in bovine oocytes. Lipids were evaluated using confocal microscopy and transmission electron microscopy. The expression of genes related to lipid metabolism, namely acyl-CoA synthetase short chain family member 2 (ACSS2), ELOVL fatty acid elongase 1 (ELOVL1) and fatty acid binding protein 3 (FABP3), was quantified by quantitative polymerase chain reaction. The mean (+/- s.d.) area occupied by lipids in immature oocytes (13 +/- 2%) was similar to those matured in vivo (MatS, 16 +/- 2%; MatT, 12 +/- 2%). However, there was a significant increase in lipids in oocytes in the MatV group (24 +/- 2%) compared with all other groups (P < 0.001). In the ultrastructural evaluations, MatV oocytes also showed the highest lipid content. The expression of ELOVL1 and FABP3 was similar in the MatS and IFIOT groups. However, transcript levels of ACSS2 were lower in IFIOT than MatV oocytes. These results indicate, for the first time, that oocytes matured by IFIOT are similar to those matured in vivo with regard to lipid accumulation, which indicates better quality than those matured in vitro.