title: Freeze/thaw stress induces organelle remodeling and membrane recycling in cryopreserved human mature oocytes.
abstract: OBJECTIVE
  Our aim was to evaluate the ultrastructure of human metaphase II oocytes subjected to slow freezing and fixed after thawing at different intervals during post-thaw rehydration.
  
  
  METHODS
  Samples were studied by light and transmission electron microscopy.
  
  
  RESULTS
  We found that vacuolization was present in all cryopreserved oocytes, reaching a maximum in the intermediate stage of rehydration. Mitochondria-smooth endoplasmic reticulum (M-SER) aggregates decreased following thawing, particularly in the first and intermediate stages of rehydration, whereas mitochondria-vesicle (MV) complexes augmented in the same stages. At the end of rehydration, vacuoles and MV complexes both diminished and M-SER aggregates increased again. Cortical granules (CGs) were scarce in all cryopreserved oocytes, gradually diminishing as rehydration progressed.
  
  
  CONCLUSIONS
  This study also shows that such a membrane remodeling is mainly represented by a dynamic process of transition between M-SER aggregates and MV complexes, both able of transforming into each other. Vacuoles and CG membranes may take part in the membrane recycling mechanism.
authors: Department of Anatomy, Histology, Forensic Medicine and Orthopaedics, Sapienza University, Rome, Italy. stefania.nottola@uniroma1.it.
authors: Stefania Annarita
authors: SA
authors: Nottola
authors: Humanitas Research Hospital, Department of Gynecology, Division of Gynecology and Reproductive Medicine, Humanitas Fertility Center, Rozzano, Milan, Italy.
authors: Elena
authors: E
authors: Albani
authors: Tecnobios Procreazione, Centre for Reproductive Health, Bologna, Italy.|Biogenesi, Reproductive Medicine Centre, Monza, Italy.
authors: Giovanni
authors: G
authors: Coticchio
authors: Department of Life, Health and Environmental Sciences, University of L'Aquila, L'Aquila, Italy.
authors: Maria Grazia
authors: MG
authors: Palmerini
authors: Department of Life, Health and Environmental Sciences, University of L'Aquila, L'Aquila, Italy.
authors: Caterina
authors: C
authors: Lorenzo
authors: CNESPS, National Health Institute, Rome, Italy.
authors: Giulia
authors: G
authors: Scaravelli
authors: Tecnobios Procreazione, Centre for Reproductive Health, Bologna, Italy.
authors: Andrea
authors: A
authors: Borini
authors: Humanitas Research Hospital, Department of Gynecology, Division of Gynecology and Reproductive Medicine, Humanitas Fertility Center, Rozzano, Milan, Italy.
authors: Paolo Emanuele
authors: PE
authors: Levi-Setti
authors: Department of Life, Health and Environmental Sciences, University of L'Aquila, L'Aquila, Italy.
authors: Guido
authors: G
authors: Macchiarelli
mesh_terms: D002462:Cell Membrane / Q000648:ultrastructure*; D015925:Cryopreservation; D018871:Endoplasmic Reticulum, Smooth / Q000648:ultrastructure*; D005260:Female; D005615:Freezing / Q000009:adverse effects; D006801:Humans; D008677:Metaphase; D046529:Microscopy, Electron, Transmission; D008928:Mitochondria / Q000648:ultrastructure; D009865:Oocytes / Q000648:ultrastructure*; D014617:Vacuoles / Q000648:ultrastructure
keywords: Cryopreservation; Human; Oocyte; Organelles; Ultrastructure; Vacuoles