Lipids are among the most abundant and essential cell components. Specifically, cytoplasmic lipid droplets (LDs) play crucial roles in cellular energy homeostasis. The foci of this review are (1) the composition and roles of lipids during oocyte maturation and early embryonic development, (2) possible causes of cryoinjuries in lipid-rich oocytes/embryos, and (3) ways to overcome these detrimental effects. Recent reports show that LDs in oocytes and embryos are not only energy depots but also are active organelles, possessing many other functions. In addition, analysis of the current literature confirms that lipid phase transition followed by phase separation during cryopreservation is one of the major causes of cryodamage in lipid-rich oocytes and embryos. While LDs and cell membranes are sensitive to chilling and freezing conditions, recent advances in vitrification and delipidation of lipid-rich oocytes and embryos partly mitigate cryodamage. The multidisciplinary approach is critical to reveal mechanisms underlying cryodamage and provides a theoretical basis for optimal cryopreservation of lipid-rich oocytes/embryos.

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The Far-Eastern wildcat (Prionailurus bengalensis euptilurus) is a rare and poorly investigated nondomestic felid species. An attempt of freezing and cryopreserving Far-Eastern wildcat spermatozoa in CaniPlus Freeze (CPF) medium is reported. Sperm was collected by electroejaculation from five adult Far-Eastern wildcat captive-born males. Epididymal spermatozoa from five adult randomly bred domestic cat males were used as a reference. The viability of frozen-thawed spermatozoa evaluated by double staining with SYBR Green I and PI followed by the subsequent confocal laser scanning microscopy (CLSM) was 38.2% ± 3.0% for the domestic cat and 38.0% ± 10.2% for the Far-Eastern wildcat. The motility of frozen-thawed spermatozoa was 30.8% ± 9.8% for the domestic cat and 33.7% ± 15.1% for the Far-Eastern wildcat. Sperm morphology was assessed by light microscopy. The total percentage of normal spermatozoa after freezing and thawing was 51.9 ± 5.9 for the domestic cat and 55.0% ± 6.4% for the Far-Eastern wildcat. Defects of flagella were the most frequently observed abnormalities in both species (32.2% ± 4.8% and 30.8% ± 4.4% of all reported anomalies for the domestic cat and Far-Eastern wildcat, respectively). Domestic cat epididymal and Far-Eastern ejaculatory spermatozoa fertilized in vitro-matured oocytes of the domestic cat (30.0% ± 5.5% and 35.5% ± 15.0%, respectively). Taken together, these results suggest that the freezing of Far-Eastern wildcat spermatozoa with CPF medium is a suitable method for Felidae cryopreservation.