Cryosurvival of Ex Situ and In Situ Feline Oocytes

Abstract

Contents Cryosurvival of feline oocytes preserved as isolated cells (ex situ) or enclosed in ovarian follicles (in situ) has been demonstrated, and significant advances have recently been achieved. However, an ideal protocol for oocyte cryopreservation has not been established to date because of extreme sensitivity of the structural complex to chilling injury. Several factors, such as stage of maturation, membrane permeability and plasticity of the cytoskeleton, affect cryosurvival of the oocyte. Also, intercellular communications between cumulus cells and oocyte are compromised after freezing or vitrification of ex situ or in situ cumulus–oocyte complexes, which has a detrimental effect on oocyte maturational competence. Despite these issues, embryo development, pregnancies and live kittens have been obtained after in vitro fertilization (by ICSI) and transfer of embryos derived from cryopreserved oocytes. It is a general belief that the efficiency of cryopreservation would increase through a better understanding of oocyte responses to cryoprotectants, cooling rates and all the physical events occurring during the exposure of feline oocytes to low temperatures. Cryobanking of feline oocytes would significantly contribute to the preservation of rare genotypes and to the maintenance of a valuable source of genetic material for research applications.

Assisted Reproductive Techniques on South American Wild Mammals

“…The rescue and manipulation of matured oocytes represent an important genetic source from wild species; nevertheless, it faces many obstacles, particularly the limited knowledge on the species reproductive physiology [82]. Thus, the use of immature oocytes from antral follicles or PFs allows the recovery of gametes from prepubertal, pregnant, old, or even dead animals [83,84] The characteristics of the ovarian follicles population in various South American wild mammals are described in Table 2 and illustrated in Figure 2.…”

Meiotic Status Does Not Affect the Vitrification Effectiveness of Domestic Cat Oocytes

“…Studies conducted on other species such as pig or cattle suggest the outcome of cryopreservation is influenced by the stage of meiotic maturation of oocytes [ 15 , 16 ], but no appropriate data is available for the vitrified oocytes of domestic cats [ 17 , 18 ]. Recently the cryosurvival rate of in-vitro matured oocytes immediately after thawing was reported to be >60%, while parthenogenetic activation of warmed vitrified oocytes resulted in a cleavage rate of 22% [ 19 ], whereas the IVM rate of immature cat oocytes after vitrification was reported by another author [ 20 ] to be about 20% and half of them cleaved after fertilization To our best knowledge, there is no published evidence comparing vitrification of immature and in vitro matured oocytes of this species under identical lab conditions.…”

Effects of vitrification and a Rho-associated coiled-coil containing protein kinase 1 inhibitor on the meiotic and developmental competence of feline oocytes

“…As a result, freezing and thawing frequently result in irreversible cryodamage at the cellular and subcellular levels. Although several types of cryoinjuries have been identified, such as disruption of cell organelles [ 3 , 4 ], the cytoskeleton [ 5 , 6 , 7 , 8 ], and the plasma membrane [ 7 , 9 , 10 ], the exact mechanisms that cause cell injury remain largely unknown. Freezing techniques including controlled-rate cryopreservation and vitrification are frequently used for oocyte cryopreservation.…”

“…Freezing techniques including controlled-rate cryopreservation and vitrification are frequently used for oocyte cryopreservation. However, extensive intracellular ice formation renders irreversible cell damage to mammalian oocytes during cooling at a suboptimal rate [ 2 , 3 , 6 , 9 ]. Therefore, a novel approach for ice-free cryopreservation by means of vitrification has been increasingly used.…”

“…However, high cryoprotectant concentrations and extremely high rates of freezing are required for this method [ 2 , 3 , 11 ]. These factors contribute to the poor quality of oocytes after vitrification, as the high cryoprotectant concentration is frequently toxic and can cause excessive osmotic stress [ 6 , 11 ]. This method of cryopreservation has also been reported to activate apoptotic pathways, including intrinsic and extrinsic mechanisms [ 7 ].…”