Gene expression differences in oocytes derived from adult and prepubertal Japanese Black cattle during in vitro maturation

Use of assisted reproductive technologies (ARTs) to shorten the generational interval in ruminants: current status and perspectives

The challenges posed by climate change and increasing world population are stimulating renewed efforts for improving the sustainability of animal production. To meet such challenges, the contribution of genomic selection approaches, in combination with assisted reproductive technologies (ARTs), to spreading and preserving animal genetics is essential. The largest increase in genetic gain can be achieved by shortening the generation interval. This review provides an overview of the current status and progress of advanced ARTs that could be applied to reduce the generation time in both female and male of domestic ruminants. In females, the use of juvenile in vitro embryo transfer (JIVET) enables to generate offspring after the transfer of in vitro produced embryos derived from oocytes of prepubertal genetically superior donors reducing the generational interval and acceleration genetic gain. The current challenge is increasing in vitro embryo production (IVEP) from prepubertal derived oocytes which is still low and variable. The two main factors limiting IVEP success are the intrinsic quality of prepubertal oocytes and the culture systems for in vitro maturation (IVM). In males, advancements in ARTs are providing new strategies to in vitro propagate spermatogonia and differentiate them into mature sperm or even to recapitulate the whole process of spermatogenesis from embryonic stem cells. Moreover, the successful use of immature cells, such as round spermatids, for intracytoplasmic injection (ROSI) and IVEP could allow to complete the entire process in few months. However, these approaches have been successfully applied to human and mouse whereas only a few studies have been published in ruminants and results are still controversial. This is also dependent on the efficiency of ROSI that is limited by the current isolation and selection protocols of round spermatids. In conclusion, the current efforts for improving these reproductive methodologies could lead toward a significant reduction of the generational interval in livestock animals that could have a considerable impact on agriculture sustainability.

Effect of food supplementation on in vitro embryo production and growth performance in prepubertal Nelore heifers

In vitro embryos production from prepubertal heifers can help contribute to breeding programs; however, strategies are necessary to increase their embryo production. The aim of this study was to investigate the effects of two nutritional plans on oocyte recovery, embryo production and growth performance of prepubertal Nelore heifers. Thirty-four Nelore heifers with age of 6.5 months were divided into two feeding treatments (NP1 and NP2). The NP1 diets served as the control and NP2 diets were formulated to contain an average of 1.22-fold more energy than NP1. After 3 months of supplementation, the animals underwent follicular aspiration (ovum pick-up, OPU) every 21 d for 3 months and embryos were produced in vitro. Wither height, chest depth, body weight and subcutaneous fat of animals were measured. The number of retrieved and viable oocytes per OPU were 1.49-fold and 1.42-fold greater in NP2 heifers (p = 0.018 and p = 0.049, respectively) than those in NP1 heifers. Heifers administered NP2 produced 29.7% blastocysts, a percentage higher than NP1 animals that produced 24.40% embryos (p < 0.05). Consequently, females in the NP2 treatment showed improved body development. These results indicate a positive effect of a higher energy diet on assisted reproduction and body development in prepubertal heifers.

Dynamics of the Reproductive Changes and Acquisition of Oocyte Competence in Nelore (Bos taurus indicus) Calves during the Early and Intermediate Prepubertal Periods

The purpose of this study was to characterize the reproductive physiology, oocyte competence, and chromatin compaction in Nelore calves in the early-prepubertal period (EPP) and the intermediate-prepubertal period (IPP). Calves aged 2-5 (EPP) and 8-11 months old (IPP) were assigned to Trial 1 (morpho-physiological-endocrine evaluations, n = 8) or Trial 2 (oocyte donors, n = 8) vs. the respective control groups of cows (n = 8, each). All morphological endpoints, except the antral follicle count, increased from the EPP to the IPP. The EPP LH-FSH plasma concentrations were similar to cows, whereas LH was lower and FSH was higher in the IPP than in cows. . Cows produced more Grade I (12.9% vs. 4.1% and 1.7%) and fewer Grade III COC (30.1% vs. 44.5% and 49.0%) than the EPP and IPP calves, respectively. The IPP calves' oocyte diameter was similar to those from cows but greater than those from EPP females (124.8 ± 8.5 and 126.0 ± 7.5 μm vs. 121.3 ± 7.5 μm, respectively). The expression of the chromatin compaction-related gene HDAC3 was downregulated in calves. The proportion of the blastocyst rate to the controls was lower in EPP than in IPP calves (43.7% vs. 78.7%, respectively). Progressive oocyte competence was found during the prepubertal period, which can help to decide whether to recover oocytes from calves.

Bioengineering Approaches to Improve In Vitro Performance of Prepubertal Lamb Oocytes

Juvenile in vitro embryo technology (JIVET) provides exciting opportunities in animal reproduction by reducing the generation intervals. Prepubertal oocytes are also relevant models for studies on oncofertility. However, current JIVET efficiency is still unpredictable, and further improvements are needed in order for it to be used on a large-scale level. This study applied bioengineering approaches to recreate: (1) the three-dimensional (3D) structure of the cumulus–oocyte complex (COC), by constructing—via bioprinting technologies—alginate-based microbeads (COC-microbeads) for 3D in vitro maturation (3D-IVM); (2) dynamic IVM conditions, by culturing the COC in a millifluidic bioreactor; and (3) an artificial follicular wall with basal membrane, by adding granulosa cells (GCs) and type I collagen (CI) during bioprinting. The results show that oocyte nuclear and cytoplasmic maturation, as well as blastocyst quality, were improved after 3D-IVM compared to 2D controls. The dynamic 3D-IVM did not enhance oocyte maturation, but it improved oocyte bioenergetics compared with static 3D-IVM. The computational model showed higher oxygen levels in the bioreactor with respect to the static well. Microbead enrichment with GCs and CI improved oocyte maturation and bioenergetics. In conclusion, this study demonstrated that bioengineering approaches that mimic the physiological follicle structure could be valuable tools to improve IVM and JIVET.

Transcriptome profiles of pre-pubertal and adult in vitro matured ovine oocytes obtained from FSH-stimulated animals

Pre-pubertal females produce more oocytes than adult individuals, but the ability of oocytes to undergo embryonic development and produce viable offspring is less in pre-pubertal animals than in adult animals. Oocyte quality is associated with abnormal gene expression. To date, the transcriptome profiles of 1-month-old lamb oocytes after in vitro maturation (IVM) are poorly reported. This study aimed to identify differentially expressed genes (DEGs) in lamb oocytes with varying competencies, affecting oocyte competence. Using RNA sequencing (RNA developmental -seq) technology, the transcriptome profiles of 1-month-old lamb oocytes after IVM were assessed, and oocytes from adult sheep large follicles were used as controls. We found 11 up-regulated and 39 down-regulated DEGs in lamb oocytes. Gene Ontology analysis of DEGs showed that molecular functions were clustered in catalytic and binding activities, while biological processes were clustered in metabolic process, cellular process, single-organism process and biological regulation. Kyoto Encyclopedia of Genes and Genomes analysis showed that the DEGs were involved in oxidative phosphorylation, transforming growth factor-beta signalling pathway, or DNA replication. In lamb MII oocytes, down-regulation of oxidative phosphorylation genes (ATP5E, NDUFA7 and COX6C), thiol protease inhibitor (CSTB) and 26S proteasome component (SHFM1) and up-regulation of CUL1, MARCH7 and TRIM17 might cause low competence of lamb embryos. In conclusion, this study provided detailed information on mRNA transcriptomes in lamb oocytes after IVM, which offers insights into the reduced developmental potential of lamb oocytes.

Impact of oxidative stress on oocyte competence for in vitro embryo production programs

Producing high-competent oocytes during the in vitro maturation (IVM) is considered a key step for the success of the in vitro production (IVP) of embryos. One of the known disruptors of oocyte developmental competence on IVP is oxidative stress (OS), which appears due to the imbalance between the production and neutralization of reactive oxygen species (ROS). The in vitro conditions induce supraphysiological ROS levels due to the exposure to an oxidative environment and the isolation of the oocyte from the follicle protective antioxidant milieu. In juvenile in vitro embryo transfer (JIVET), which aims to produce embryos from prepubertal females, the oocytes are more sensitive to OS as they have inherent lower quality. Therefore, the IVM strategies that aim to prevent OS have great interest for both IVP and JIVET programs. The focus of this review is on the effects of ROS on oocyte IVM and the main antioxidants that have been tested for protecting the oocyte from OS. Considering the importance that OS has on oocyte competence, it is crucial to create standardized antioxidant IVM systems for improving the overall IVP success.

Dynamic changes in the global transcriptome of bovine germinal vesicle oocytes after vitrification followed by in vitro maturation

This study was conducted to investigate the effect of vitrification on the dynamics of the global transcriptome in bovine germinal vesicle (GV) oocytes and their in vitro-derived metaphase II (MII) oocytes. The GV oocytes were vitrified using the open-pulled straw method. After warming, GV oocytes and the resulting MII-stage oocytes were cultured in vitro for 2h and 24h respectively and were then collected. The fresh GV oocytes and their in vitro-derived MII oocytes were used as controls. Then, each pool (fresh GV, n=3; vitrified GV, n=4; fresh MII, n=1 and MII derived from vitrified GV, n=2) from the different stages was used for mRNA transcriptome sequencing. The results showed that the in vitro maturation rates of GV oocytes were significantly decreased (32.36% vs 53.14%) after vitrification. Bovine GV oocyte vitrification leads to 12 significantly upregulated and 19 downregulated genes. After culturing in vitro, the vitrification-derived MII oocytes showed 47 significantly upregulated and six downregulated genes when compared with those from fresh GV oocytes. Based on molecular function-gene ontology terms analysis and the Kyoto encyclopaedia of genes (KEGG) pathway database, the differentially expressed genes were associated with the pathways of cell differentiation and mitosis, transcription regulation, regulation of actin cytoskeleton, apoptosis and so on, which potentially result in the lower in vitro development of GV bovine oocytes.

Age-related changes in gene expression patterns of immature and aged rat primordial follicles

Women are born with millions of primordial follicles which gradually decrease with increasing age and this irreversible supply of follicles completely exhausts at menopause. The fertility capacity of women diminishes in parallel with aging. The mechanisms for reproductive aging are not fully understood. We have observed a decline in Brca1 mediated DNA repair in aging rat primordial follicles. To further understand the age-related molecular changes, we performed microarray gene expression analysis using total RNA extracted from immature (18 to 20 day old) and aged (400 to 450 day old) rat primordial follicles. The results of current microarray study revealed that there were 1,011 (>1.5 fold, p<0.05) genes differentially expressed between two groups in which 422 genes were up-regulated and 589 genes were down-regulated in aged rat primordial follicles compared to immature primordial follicles. The gene ontology and pathway analysis of differentially expressed genes revealed a critical biological function such as cell cycle, oocyte meiosis, chromosomal stability, transcriptional activity, DNA replication, and DNA repair were affected by age. This considerable difference in gene expression profiles may have an adverse influence on oocyte quality. Our data provide information on the processes that may contribute to aging and age-related decline in fertility.

Molecular markers for oocyte competence in bovine cumulus cells

This study aimed to quantify the expression of candidate genes in cumulus cells (CCs) from cumulus-oocyte complexes (COCs) with high and low potential for in vitro development up to the blastocyst stage. First, the effects of individual culture and biopsy on embryo development were evaluated. Individuals cultured using the well of the well system were compared with individuals cultured in 20 μL droplets (microdroplets) and those cultured in groups (control). Blastocyst rates were lower for the individual culture systems (P < 0.05; well of the well = 17.9%, n = 95; microdrop = 26.3%, n = 95) than for the control group (45.0%, n = 209). Second, the effects of biopsy on embryo production were compared between the control and microdroplet cultures, and no effects (P > 0.05) were observed for either group. Finally, the expression profiles of glypican 4 (GPC4), IGF4-binding protein, follicle-stimulating hormonereceptor, growth hormone receptor, epidermal growth factor receptor, fibroblast growth factor 11, solute carrier family 2 member 1, solute carrier family 2 member 3,sprouty homolog 1, versican, and keratin protein 8 in CCs obtained by biopsy were quantified by real-time polymerase chain reaction. Cumulus cells were categorized on the basis of the fates of the COCs: expanded blastocyst, cleaved and arrested, and uncleaved. The GPC4 gene was overexpressed (P = 0.007) in CCs from oocytes that formed embryos compared with those that produced cleaved and arrested embryos. We concluded that individual culture reduced blastocyst production; however, biopsy did not affect embryo development. The profile of GPC4 expression can be used as a marker to distinguish COCs with potential for embryo development from those with limited developmental potential.

An integrated approach to bovine oocyte quality: from phenotype to genes

In cattle, early embryonic failure plays a major role in the limitation of reproductive performance and is influenced by genetic effects. Suboptimal oocyte quality, including an inadequate store of maternal factors, is suspected to contribute to this phenomenon. In the present study, 13 Montbeliarde cows were phenotyped on oocyte quality, based on their ability to produce viable embryos after in vitro maturation, fertilisation and culture for 7 days. This discriminated two groups of animals, exhibiting developmental rates below 18.8% or above 40.9% (relative to cleaved embryos). Using microarrays, transcriptomic profiles were compared between oocytes collected in vivo from these two groups of animals. The difference in oocyte development potential was associated with changes in transcripts from 60 genes in immature oocytes and 135 genes in mature oocytes (following Bonferroni 5% correction). Of these, 16 and 32 genes were located in previously identified fertility quantitative trait loci. A subset of differential genes was investigated on distinct samples by reverse transcription-quantitative polymerase chain reaction. For SLC25A16, PPP1R14C, ROBO1, AMDHD1 and MEAF6 transcripts, differential expression was confirmed between high and low oocyte potential animals. Further sequencing and searches for polymorphisms will pave the way for implementing their use in genomic selection.

Application of Top-Down and Bottom-up Systems Approaches in Ruminant Physiology and Metabolism

Systems biology is a computational field that has been used for several years across different scientific areas of biological research to uncover the complex interactions occurring in living organisms. Applications of systems concepts at the mammalian genome level are quite challenging, and new complimentary computational/experimental techniques are being introduced. Most recent work applying modern systems biology techniques has been conducted on bacteria, yeast, mouse, and human genomes. However, these concepts and tools are equally applicable to other species including ruminants (e.g., livestock). In systems biology, both bottom-up and top-down approaches are central to assemble information from all levels of biological pathways that must coordinate physiological processes. A bottom-up approach encompasses draft reconstruction, manual curation, network reconstruction through mathematical methods, and validation of these models through literature analysis (i.e., bibliomics). Whereas top-down approach encompasses metabolic network reconstructions using ‘omics’ data (e.g., transcriptomics, proteomics) generated through DNA microarrays, RNA-Seq or other modern high-throughput genomic techniques using appropriate statistical and bioinformatics methodologies. In this review we focus on top-down approach as a means to improve our knowledge of underlying metabolic processes in ruminants in the context of nutrition. We also explore the usefulness of tissue specific reconstructions (e.g., liver and adipose tissue) in cattle as a means to enhance productive efficiency.