Replication of somatic micronuclei in bovine enucleated oocytes

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.

Improved embryo development using high cysteamine concentration during IVM and sperm co-culture with COCs previous to ICSI in bovine

In contrast to other species, intracytoplasmic sperm injection (ICSI) in bovine remains inefficient, resulting in low embryo developmental rates. It is unclear whether such inefficiency is due to the poor response of bovine ooplasms to the injection stimulus, or to the inability of bull sperm to induce oocyte activation. In order to facilitate these events, two strategies were assessed: the use of high concentration of cysteamine [Cys] during IVM; and the selection of sperm attached to cumulus cells after incubation with COCs for ICSI. First, COCs were IVM with increasing [Cys] and subjected to IVF. Zygotes from all groups were cultured under different O₂ tensions and development to blastocyst was evaluated. In a second experiment, sperm were co-cultured for 3 h with COCs and acrosome reaction was studied. Afterwards, the best IVM and IVC conditions determined on Experiment 1 were used for ICSI assay. COCs were matured for 21 h with 1 (Cys 1) or 0.1 mM Cys (Cys 0.1 groups, standard condition). In addition, COCs were incubated for ≥3 h with 16 × 10⁶ sperm/ml and only sperm attached to cumulus cells were selected for ICSI (ICSI + Co-cult groups). After chemical activation, embryos were cultured in SOF medium under low O₂ tension. Cleavage and blastocyst rates were evaluated at days 2 and 7 of IVC, respectively. Finally, the relative expression of eight genes indicators of embryo quality was compared between ICSI and IVF control blastocysts by qPCR. Cleavage rates were higher for Cys 0.1 ICSI + Co-cult and Cys 1 ICSI + Co-cult groups (n = 117, 92% and n = 116, 79%, respectively) compared to their controls (n = 132, 60% for Cys 0.1 ICSI and n = 108, 52% for Cys 1 ICSI) (p ≤ 0.05). Interestingly, the combined treatment (Cys 1 ICSI + Co-cult) showed higher blastocyst rates than all other ICSI groups (23 vs. 11, 18 and 14% for Cys 0.1 ICSI + Co-cult, Cys 1 ICSI, and Cys 0.1 ICSI, respectively) (p ≤ 0.05). Moreover, incubation with COCs increased the rates of live acrosome reacted sperm (p ≤ 0.05). The relative abundance of mRNAs coding for INFτ, CAT, DNMT1, OCT4, and HDAC3 did not differ between treatments (p ≤ 0.05). SOD2, HADC1 and HADC2 expression was higher for Cys 0.1 ICSI than for IVF embryos (p ≤ 0.05). Group Cys 1 ICSI did not differ from IVF for those three genes, neither did Cys 1 ICSI + Co-cult, except for HDAC1 (p ≤ 0.05). In conclusion, the use of 1 mM Cys during IVM and of sperm incubated with mature COCs might be a good strategy to improve ICSI outcomes in cattle.