Maturation of the reconstructed oocytes by germinal vesicle transfer in rabbits and mice

State of the art of nuclear transfer technologies for assisting mammalian reproduction

The transfer of nuclear genomic DNA from a cell to a previously enucleated oocyte or zygote constitutes one of the main tools for studying epigenetic reprogramming, nucleus-cytoplasm compatibility, pluripotency state, and for genetic preservation or edition in animals. More than 50 years ago, the first experiences in nuclear transfer began to reveal that factors stored in the cytoplasm of oocytes could reprogram the nucleus of another cell and support the development of an embryo with new genetic information. Furthermore, when the nuclear donor cell is an oocyte, egg, or a zygote, the implementation of these technologies acquires clinical relevance for patients with repeated failures in ART associated with poor oocyte quality or mitochondrial dysfunctions. This review describes the current state, scope, and future perspectives of nuclear transfer techniques currently available for assisting mammal reproduction.

Do the Cytoplast and Nuclear Material of Germinal Vesicle Oocyte Support Developmental Competence Upon Reconstruction with Embryonic/Somatic Nucleus

Maturation conditions and oocytes quality have substantial roles on developmental competence of unreconstructed or reconstructed oocytes. Cloning has been reported successfully with low efficiency through embryonic or somatic nuclear transfer into enucleated metaphase II oocytes. It has been suggested that introducing embryonic or somatic nucleus to cytoplast at earlier stage might improve reprogramming of the introduced nucleus. In addition, the synchronization between the donor nucleus and recipient cytoplasts might effect on reprogramming and further embryonic development. Therefore, the question arises; does the cytoplast of germinal vesicle (GV) oocyte containing nuclear sap improve developmental competence upon reconstruction with embryonic/somatic nucleus compared with MII cytoplast. It has been indicated that GV material is essential for remodeling of sperm or embryonic or somatic nucleus in GV oocyte cytoplast and their further embryonic developmental competence. GV cytoplasts could be obtained through micromanipulation. Different micromanipulation techniques of immature oocytes at different stages were adapted in addition to introducing donor nuclei at G0/G1, S and G2/M phase, and enucleolation technique as well. Upon micromanipulation, it could obtain GV cytoplasts; cumulus-free and without GV material, cumulus-complexes and without GV material, cumulus-free and with GV material, and cumulus-complexes and with GV material in addition to enucleolated GV oocytes. Therefore, this short review will address briefly the importance of maturation conditions, cumulus cells, oocyte quality, the techniques of enucleation GV oocyte, the cell cycle stage of the introduced donor cell, or nucleus for oocyte maturation and embryo development.

Cryopreservation of immature bovine oocytes to reconstruct artificial gametes by germinal vesicle transplantation

Joining immature gamete cryopreservation and germinal vesicle transplantation (GVT) technique could greatly improve assisted reproductive technologies in animal breeding and human medicine. The present work was aimed to assess the most suitable cryopreservation protocol between slow freezing and vitrification for immature denuded bovine oocytes, able to preserve both nuclear and cytoplasmic competence after thawing. In addition, the outcome of germinal vesicle transfer procedure and gamete reconstruction was tested on the most effective cryopreservation system. Oocytes, isolated from slaughterhouse ovaries, were stored after cumulus cells removal either by slow freezing or by vitrification in open pulled straws. After thawing, oocytes were matured for 24 h in co-culture with an equal number of just isolated intact cumulus enclosed oocytes, and fixed in order to evaluate the stage of meiotic progression and cytoskeleton organization. Our results showed that after warming, vitrified oocytes reached metaphase II (MII) in a percentage significantly higher than oocytes cryopreserved by slow freezing (76.2% and 36.5% respectively, p < 0.05). Moreover, vitrification process preserved the organization of cytoskeleton elements in a higher proportion of oocytes than slow freezing procedure. Therefore vitrification has been identified as the elective method for denuded immature oocytes banking and it has been applied in the second part of the study. Our results showed that 38.3% of oocytes reconstructed from vitrified gametes reached the MII of meiotic division, with efficiency not different from oocytes reconstructed with fresh gametes. We conclude that vitrification represents a suitable method of GV stage denuded oocyte banking since both nuclear and cytoplasmic components derived from cryopreserved immature oocytes can be utilized for GVT.

Time course of meiotic progression after transferring primary spermatocyte into ooplasm at different stages

This study attempted to investigate the time course of meiotic progression after transferring primary spermatocyte (PS) into ooplasm at different maturing stages. In present experiments, PSs were introduced into maturing ooplasts or oocytes by electrofusion. Higher fusion rate was obtained by phytohemagglutinin (PHA) agglutination than by perivitelline space (PVS) insertion. When the ooplasms prepared at 0, 2, 5, and 8.5 hr of in vitro maturation (IVM) were used as recipients and PSs were used as donors, the reconstructed cells extruded the first polar body (PB1) approximately 8.5, 7, 5.5, and 3 hr after electrofusion, respectively. Especially, when ooplasm cultured for 8.5 hr in vitro after GV removal was fused with PS, the PB1 was emitted 7-11 hr after electrofusion. Additionally, the PB1 extrusions of GV and pro-MI oocytes fertilized with PSs were 2.5 hr earlier than control oocytes. The results suggest that (1) PSs undergo the first meiosis in different time courses when introduced into ooplasm at different maturing stages; (2) GV material plays an important role in determining the timing of PB1 extrusion; and (3) first meiotic division of GV and pro-MI oocytes can be accelerated by introducing PS.