title: 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.
authors.affiliation: Department of Life, Health and Environmental Sciences, University of L'Aquila, L'Aquila, Italy.
authors.forename: Maria Grazia
authors.initials: MG
authors.lastname: Palmerini
authors.forename: Monica
authors.initials: M
authors.lastname: Antinori
authors.forename: Marta
authors.initials: M
authors.lastname: Maione
authors.forename: Fabrizio
authors.initials: F
authors.lastname: Cerusico
authors.forename: Caterina
authors.initials: C
authors.lastname: Versaci
authors.forename: Stefania Annarita
authors.initials: SA
authors.lastname: Nottola
authors.forename: Guido
authors.initials: G
authors.lastname: Macchiarelli
authors.forename: Mohammad Ali
authors.initials: MA
authors.lastname: Khalili
authors.forename: Severino
authors.initials: S
authors.lastname: Antinori
mesh_terms: D000328:Adult; D005260:Female; D006801:Humans; D008854:Microscopy, Electron; D008871:Microvilli / Q000648:ultrastructure; D009865:Oocytes / Q000502:physiology / Q000648:ultrastructure*; D058989:Vitrification