A brief history of oocyte cryopreservation: Arguments and facts

Preservation of female genetic resources in feline species

The development of assisted reproduction techniques (ART) specifically for felids has been propagated for two main reasons: (i) most felids are threatened and faced with extinction in all or part of their native habitats (IUCN Red List of Threatened Species, www.catsg.org), and (ii) the domestic cat (Felis catus) can serve as a research model for the implementation of advanced assisted reproductive techniques (ART) to be applied in exotic cats. Domestic cat ovaries can be freshly obtained from veterinary clinics and are frequently used for research on preservation of genetic resources in feline species. The presented review will summarize recent advances and obstacles in biobanking of female genetic resources and discuss alternative approaches which are under investigation.

Fertility preservation for young adults, adolescents, and children with cancer

Options for fertility preservation (FP) through cryopreservation methods are currently available for young adults, adolescents, and children. Guidelines for FP have been provided by international clinical societies, and emergency procedures aimed at FP have been implemented into clinical practice worldwide. In this article, we review the current data on clinical standards of emergency FP in patients who are facing gonadotoxic effects of cancer treatment, and we also describe the methods that are still under development, usually denoted as experimental. In Sweden, programmes for FP have been established at large university hospitals, thus covering the whole country. The Swedish publicly financed health care covers both assisted reproduction for treatment of infertility and the cryopreservation of gametes or gonadal tissue when there is a medical indication, such as the risk to become infertile due to oncologic treatment; hence the access to FP is ensured for the whole population. At our centre at Karolinska University Hospital in Stockholm, methods for FP have been offered since 1988. In this article, we also review the oncologic indications for FP in our patient cohort of >3000 individuals during the period 1988-2018.

DNA fragmentation index (DFI) as a measure of sperm quality and fertility in mice

Although thousands of genetically modified mouse strains have been cryopreserved by sperm freezing, the likelihood of cryorecovery success cannot be accurately predicted using conventional sperm parameters. The objective of the present study was to assess the extent to which measurement of a sperm DNA fragmentation index (DFI) can predict sperm quality and fertility after cryopreservation. Using a modified TUNEL assay, we measured and correlated the DFI of frozen-thawed sperm from 83 unique mutant mouse strains with sperm count, motility and morphology. We observed a linear inverse correlation between sperm DFI and sperm morphology and motility. Further, sperm DFI was significantly higher from males with low sperm counts compared to males with normal sperm counts (P < 0.0001). Additionally, we found that viable embryos derived using sperm from males with high DFI (62.7 ± 7.2% for IVF and 73.3 ± 8.1% for ICSI) failed to litter after embryo transfer compared to embryos from males with low DFI (20.4 ± 7.9% for IVF and 28.1 ± 10.7 for ICSI). This study reveals that measurement of DFI provides a simple, informative and reliable measure of sperm quality and can accurately predict male mouse fertility.

Raman spectroscopy-based approach to study the female gamete

In the last years, an increasing interest has emerged on the development of new non-invasive methods for the assessment of oocyte quality in order to improve outcomes of assisted reproductive technologies (ARTs) either in medical or veterinary fields. Raman microspectroscopy (RMS) has been proposed as a promising tool for the examination of the mammalian female gamete and identification of markers of its developmental competence. This technique provides a unique spectral fingerprint indicative of molecular composition of the cell and allows probing subcellular compartments. Studies have been carried out analysing by RMS fixed or living oocytes derived from different animal models. RMS imaging has been successfully applied to discriminate the biochemical changes of the global molecular architecture of mouse oocytes at different stages of maturation and those occurring in different conditions of maturation and oocyte aging. RMS can also detect modifications of specific structural components, including the oocyte zona pellucida and F-actin subcortical cytoskeleton in fresh sheep oocytes and those underwent to vitrification procedures. Finally, the recent application of Coherent anti-Stokes Raman scattering (CARS) microscopy for examination of oocyte lipid component will be briefly discussed. CARS overcomes some limits of RMS providing vibrational and spectral information with higher sensitivity, spatial resolution which is ideal to study living oocytes. This review summarizes the research on RMS approaches for oocyte evaluation showing the high potential use, current limitations and new improvements.

Morphological features and microtubular changes in vitrified ovine oocytes

Cryobanking of oocytes collected from prepubertal donors may supply a virtually unlimited number of female gametes for both basic research and commercial applications. Prepubertal oocytes show some structural and functional limitations compared to the adult ones that may impair their ability to recover damages from cryopreservation. In oocytes, the meiotic spindle is acutely sensitive to temperature deviation, but capable of regeneration following cryopreservation. In the present work, we studied the effects of vitrification and post-warming incubation on the microtubular cytoskeleton and the tubulin post-translational modifications (tyrosination and acetylation) in prepubertal and adult oocytes. Obtained results showed that prepubertal oocytes are more affected by vitrification-induced injuries than adult ones. In fact, prepubertal oocytes showed more severe alterations of the meiotic spindle conformation and a higher percentage of parthenogenetic activation compared to adult ones. Moreover, in the adult oocytes the equilibrium between tyrosinated and acetylated α-tubulin was restored after 4 h of post-warming incubation. Diversely, in prepubertal oocytes the imbalance between tyrosinated and acetylated α-tubulin was increased during post-warming incubation. Our study shows that prepubertal oocytes react differently to the insults provoked by vitrification compared to adult oocytes, showing an impaired ability to recover from vitrification-induced injuries. In the evaluation of oocyte ability to recover from vitrification-induced injuries, tubulin post-translational modifications represent an important indicator for assessing oocyte quality.