Ultrastructure of immature and mature human oocytes after cryotop vitrification

Abstract

In vitro maturation of vitrified immature germinal vesicle (GV) oocytes is a promising fertility preservation option. We analyzed the ultrastructure of human GV oocytes after Cryotop vitrification (GVv) and compared it with fresh GV (GVc), fresh mature metaphase II (MIIc) and Cryotop-vitrified mature (MIIv) oocytes. By phase contrast microscopy and light microscopy, the oolemmal and cytoplasmic organization of fresh and vitrified oocytes did not show significant changes. GVv oocytes showed significant ultrastructural alterations of the microvilli in 40% of the samples; small vacuoles and occasional large/isolated vacuoles were abnormally present in the ooplasm periphery of 50% of samples. The ultrastructure of nuclei and mitochondria-vesicle (MV) complexes, as well as the distribution and characteristics of cortical granules (CGs), were comparable with those of GVc oocytes. MIIv oocytes showed an abnormal ultrastructure of microvilli in 30% of the samples and isolated large vacuoles in 70% of the samples. MV complexes were normal, but mitochondria-smooth endoplasmic reticulum aggregates appeared to be of reduced size. CGs were normally located under the oolemma but presented abnormalities in distribution and matrix electron density. In conclusion, Cryotop vitrification preserved main oocyte characteristics in the GV and MII stages, even if peculiar ultrastructural alterations appeared in both stages. This study also showed that the GV stage appears more suitable for vitrification than the MII stage, as indicated by the good ultrastructural preservation of important structures that are present only in immature oocytes, like the nucleus and migrating CGs.

Effect of vitrification on the mRNA transcriptome of bovine oocytes

“…The former is required for energy metabolism (Nagai et al., ) and the latter for intracellular Ca 2+ signalling (Lowther, Weitzman, Maier, & Mehlmann, ), which are required for oocyte activation and early embryonic development. Our results partially explain the degenerated mitochondria (Gualtieri et al., ) and insufficient ER reorganization (Kim et al., ; Palmerini et al., ) in vitrified oocytes.…”

Ultrastructural markers of quality are impaired in human metaphase II aged oocytes: a comparison between reproductive and in vitro aging

“…These aggregates, typical of mature ooplasm, are likely involved in the energy production and storage at fertilization and during first embryo cleavages. M-SER aggregates and MV complexes presumably belong to the same system of interconnected membranes [24,26,33]. In fact, SER membranes appear capable of shifting into each other, as suggested by the detection of intermediate features between tubules and vesicles by TEM [33].…”

“…Undoubtedly, transmission electron microscopy (TEM) and confocal microscopy cannot be used proactively in ART. However, TEM is effective in evaluating ooplasmic quality [17][18][19][20][21][22][23][24] and confocal microscopy is a technique of choice to assess nuclear (spindle) impairment [25]. Up to date, only rare reports described the ultrastructure of human, mature, metaphase II (MII), IvA oocytes [26,27].…”

Chromosomal meiotic segregation, embryonic developmental kinetics and DNA (hydroxy)methylation analysis consolidate the safety of human oocyte vitrification

“…The information available on the neonatal outcome and the long-term follow-up of children conceived after oocyte cryopreservation is limited (Chian et al, 2008(Chian et al, , 2014Noyes et al, 2009;Wennerholm et al, 2009;Cobo et al, 2014) and only small studies have specifically addressed the safety of oocyte vitrification (Coticchio et al, 2009;Bonetti et al, 2011;Chen et al, 2012;Forman et al, 2012;Khalili et al, 2012;Monzo et al, 2012;Dominguez et al, 2013;Gugliemo et al, 2014;Konc et al, 2014;Nohales Có rcoles et al, 2014;Palmerini et al, 2014).…”