The mechanism of oocyte activation influences the cell cycle-related genes expression during bovine preimplantation development

Nobiletin enhances the development and quality of bovine embryos in vitro during two key periods of embryonic genome activation

In vitro culture can alter the development and quality of bovine embryos. Therefore, we aimed to evaluate whether nobiletin supplementation during EGA improves embryonic development and blastocyst quality and if it affects PI3K/AKT signaling pathway. In vitro zygotes were cultured in SOF + 5% FCS (Control) or supplemented with 5, 10 or 25 µM nobiletin (Nob5, Nob10, Nob25) or with 0.03% dimethyl-sulfoxide (C_DMSO) during minor (2 to 8-cell stage; MN_EGA) or major (8 to 16-cell stage; MJ_EGA) EGA phase. Blastocyst yield on Day 8 was higher in Nob5 (42.7 ± 1.0%) and Nob10 (44.4 ± 1.3%) for MN_EGA phase and in Nob10 (61.0 ± 0.8%) for MJ_EGA phase compared to other groups. Mitochondrial activity was higher and lipid content was reduced in blastocysts produced with nobiletin, irrespective of EGA phase. The mRNA abundance of CDK2, H3-3B, H3-3A, GPX1, NFE2L2 and PPARα transcripts was increased in 8-cells, 16-cells and blastocysts from nobiletin groups. Immunofluorescence analysis revealed immunoreactive proteins for p-AKT forms (Thr308 and Ser473) in bovine blastocysts produced with nobiletin. In conclusion, nobiletin supplementation during EGA has a positive effect on preimplantation bovine embryonic development in vitro and corroborates on the quality improvement of the produced blastocysts which could be modulated by the activation of AKT signaling pathway.

Endoplasmic reticulum distribution during bovine oocyte activation is regulated by protein kinase C via actin filaments

Fertilization-induced [Ca²⁺ ]_i oscillations generally depend on the release of calcium ions from the endoplasmic reticulum (ER). Since ER is the main store of calcium ions, it plays an important role in oocyte fertilization. However, the mechanism of ER organization at oocyte activation is unknown. Here, we show that protein kinase C (PKC) is involved in ER distribution during bovine oocyte activation, but not involved in cell cycle resumption and spindle organization. Actin filaments were affected by PKC pharmacological inhibition. In addition, similar to PKC results, the actin-depolymerizing drug cytochalasin B affected the ER distribution during oocyte activation. Specifically, we have demonstrated that ER organization during bovine oocyte activation is regulated by PKC possibly through its action on actin filaments regulation. Taken together, the results presented here provide further information on the pathway involved in the regulation of ER organization during oocyte activation and new insight into the functional role of PKC and actin filaments during this process.

Expression of miRNAs in Bull Spermatozoa Correlates with Fertility Rates

Bull spermatozoa are rich in active miRNAs, and it has been shown that specific spermborne miRNAs can be linked to fertility. Thus, expression profiling of spermatozoa could be helpful for understanding male fertility and the ability of spermatozoa to initiate and sustain zygotic, embryonic and foetal development. Herein we hypothesized that bulls with moderate to high fertility can be identified by differences in amounts of certain miRNAs between their ejaculates. RNA samples from spermatozoa of eight brother pairs (one bull with high and one with moderate NRR in each pair) of the Holstein breed were prepared. miRNA was isolated, and the expression of 178 miRNAs was determined by RT-qPCR. Important findings were that highly expressed miRNAs, not linked to NRR status, were identified in the bull sperm samples, which indicate that these miRNAs have an important role in early embryogenesis. A large fraction of the targets genes were phosphoproteins and genes involved in the regulation of transcription. Seven miRNAs (mir-502-5p, mir-1249, mir-320a, mir-34c-3p, mir-19b-3p, mir-27a-5p and mir-148b-3p) were differentially expressed between bulls with moderate and high NRR with a strong tendency towards a higher expression of miRNAs in bulls with moderate fertility. Thus, bulls with a moderate NRR negatively regulate the expression of protein-coding genes, which leads to problems during the pregnancy.