Morphological features of lipid droplet transition during porcine oocyte fertilisation and early embryonic development to blastocyst in vivo and in vitro

Abstract

Lipid content in mammalian oocytes or embryos differs among species, with bovine and porcine oocytes and embryos showing large cytoplasmic droplets. These droplets are considered to play important roles in energy metabolism during oocyte maturation, fertilisation and early embryonic development, and also in the freezing ability of oocytes or embryos; however, their detailed distribution or function is not well understood. In the present study, changes in the distribution and morphology of porcine lipid droplets during in vivo and in vitro fertilisation, in contrast to parthenogenetic oocyte activation, as well as during their development to blastocyst stage, were evaluated by transmission electron microscopy (TEM). The analysis of semi-thin and ultra-thin sections by TEM showed conspicuous, large, electron-dense lipid droplets, sometimes associated with mitochondrial aggregates in the oocytes, irrespective of whether the oocytes had been matured in vivo or in vitro. Immediately after sperm penetration, the electron density of the lipid droplets was lost in both the in vivo and in vitro oocytes, the reduction being most evident in the oocytes developed in vitro. Density was restored in the pronculear oocytes, fully in the in vivo specimens but only partially in the in vitro ones. The number and size of the droplets seemed, however, to have decreased. At 2- to 4-cell and blastocyst stages, the features of the lipid droplets were almost the same as those of pronuclear oocytes, showing a homogeneous or saturated density in the in vivo embryos but a marbled or partially saturated appearance in the in vitro embryos. In vitro matured oocytes undergoing parthenogenesis had lipid droplets that resembled those of fertilised oocytes until the pronuclear stage. Overall, results indicate variations in both the morphology and amount of cytoplasmic lipid droplets during porcine oocyte maturation, fertilisation and early embryo development as well as differences between in vivo and in vitro development, suggesting both different energy status during preimplantation development in pigs and substantial differences between in vitro and in vivo development.

Fat area and lipid droplet morphology of porcine oocytes during in vitro maturation with trans-10, cis-12 conjugated linoleic acid and forskolin

“…Differences in the gray tones might suggest not only alterations of the composition, amount and morphology of LD but also its aggregation or dispersion in the ooplasm. Several authors confirmed that as maturation progresses, the ooplasm can have different shades of gray caused by uneven distribution of organelles, specifically mitochondria and LD, which reside in close proximity (Kikuchi et al, 2002;Ambruosi et al, 2009). Here it was shown that after 44 to 48 h of culture, t10,c12 CLA oocytes were lighter (dark gray 5 55.6% and light gray 5 44.4%) than those of control and forskolin treatments (dark gray 5 100%).…”

“…Further studies are needed to clarify forskolin positive action on oocyte developmental competence for embryo production and quality. Porcine oocytes present variations in both morphology and amount of cytoplasmic LD during in vivo or in vitro maturation (Kikuchi et al, 2002). In the present study, we investigated the extent of these variations by measuring LD areas and total area occupied by LD, the fat areas, as well as the relationship of fat area with total oocyte area through the fat oocyte index, before and during porcine oocyte maturation.…”

The Leading Blastomere of the 2-Cell Stage Parthenogenetic Porcine Embryo Contributes to the Abembryonic Part First

“…Early porcine embryos showing large cytoplasmic lipid droplets may have different metabolic pathways compared with their murine counterparts. These droplets are considered to play important roles in energy metabolism during oocyte maturation, fertilization and early embryonic development [11]. However, it has also been reported that endogenous triglycerides act as metabolic substrates during in vitro maturation only and not during early embryonic development in pigs [25].…”

“…The direct role of the high lipid content in early porcine embryos remains to be elucidated. In vitro maturation also changes the features of lipid droplets reflecting different energy statuses [11]. Hence, the differences in the contents or features of cytoplasmic lipids between in vivo derived murine oocytes and in vitro matured porcine oocytes might change the patterning of the Em-Ab axis.…”

Immunocytochemistry in Early Mammalian Embryos

“…Studying the ultrastructural organization of the embryonic cells [15][16][17][18][19] Labeling of nascent transcripts…”