Distribution and content of lipid droplets and mitochondria in pig parthenogenetically activated embryos after delipation

The present study examines the effect of delipation on developmental competence and the distribution pattern of lipid droplets (LDs) and mitochondria in parthenogenetically activated (PA) pig embryos. Mature oocytes were delipated by centrifugation after partial digestion of the zonae pellucidae, subjected to parthenogenetic activation after total removal of zonae pellucidae by pronase, and then cultured in vitro up to the blastocyst stage. The contents and distributions of LDs and mitochondria in the oocytes and/or embryos were observed by staining with Oil Red O and MitoTracker Red CMXRos, respectively. The LD and mitochondrial contents were significantly reduced by the delipation process, and only smaller LDs remained in the delipated oocytes and/or embryos. Their content remained constant from the metaphase II oocyte to the blastocyst stage, but they became gradually smaller as the oocytes and/or embryos developed. The distribution pattern of the LDs in the delipated embryos changed over time and in a manner different to that seen in the controls. In the early developmental stages (1- to 4-cell stages), they were distributed peripherally and formed a ring around the nucleus. However, by the blastocyst stage, a homogeneous distribution of LDs was observed in both the inner cell mass and trophectoderm. The distribution pattern of mitochondria also changed with the development of the delipated PA embryos and again, in ways different to those seen in the controls. In the early 1- to 4-cell stages, a peripheral distribution of mitochondrial foci was observed in each blastomere. However, in blastocysts, the mitochondria were homogeneously distributed throughout the inner cell mass and trophectoderm. Although the cleavage rate at the 2- and 4-cell stages of the PA embryos was not affected by delipation (95.83 ± 2.25% vs. 97.44 ± 0.67%; 79.17 ± 4.47% vs. 84.62 ± 1.19%), it was reduced significantly in the blastocyst compared with the controls (21.67 ± 3.78% vs. 49.36 ± 1.77%). The distribution pattern of the LDs in oocytes and/or embryos at different developmental stages, and that of the mitochondria in metaphase II oocytes, was affected by delipation. The developmental competence of porcine PA embryos would appear to be affected by delipation.