Differential Expression of IGF Family Members in Heat-Stressed Embryos ProducedIn Vitrofrom OPU-Derived Oocytes of Nelore (Bos indicus) and Holstein (Bos taurus) Cows

Heat Stress as a Barrier to Successful Reproduction and Potential Alleviation Strategies in Cattle

In recent decades, the adverse effects of global warming on all living beings have been unanimously recognized across the world. A high environmental temperature that increases the respiration and rectal temperature of cattle is called heat stress (HS), and it can affect both male and female reproductive functions. For successful reproduction and fertilization, mature and healthy oocytes are crucial; however, HS reduces the developmental competence of oocytes, which compromises reproduction. HS disturbs the hormonal balance that plays a crucial role in successful reproduction, particularly in reducing the luteinizing hormone and progesterone levels, which leads to severe problems such as poor follicle development with a poor-quality oocyte and problems related to maturity, silent estrus, abnormal or weak embryo development, and pregnancy loss, resulting in a declining reproduction rate and losses for the cattle industry. Lactating cattle are particularly susceptible to HS and, hence, their reproduction rate is substantially reduced. Additionally, bulls are also affected by HS; during summer, semen quality and sperm motility decline, leading to compromised reproduction. In summer, the conception rate is reduced by 20-30% worldwide. Although various techniques, such as the provision of water sprinklers, shade, and air conditioning, are used during summer, these methods are insufficient to recover the normal reproduction rate and, therefore, special attention is needed to improve reproductive efficiency and minimize the detrimental effect of HS on cattle during summer. The application of advanced reproductive technologies such as the production of embryos in vitro, cryopreservation during the hot season, embryo transfer, and timed artificial insemination may minimize the detrimental effects of HS on livestock reproduction and recover the losses in the cattle industry.

Effects of Heat Stress on Bovine Oocytes and Early Embryonic Development-An Update

Heat stress is a major threat to cattle reproduction today. It has been shown that the effect of high temperature not only has a negative effect on the hormonal balance, but also directly affects the quality of oocytes, disrupting the function of mitochondria, fragmenting their DNA and changing their maternal transcription. Studies suggest that the induction of HSP70 may reduce the apoptosis of granular layer cells caused by heat stress. It has been shown that the changes at the transcriptome level caused by heat stress are consistent with 46.4% of blastocyst development disorders. Cows from calves exposed to thermal stress in utero have a lower milk yield in their lifetime, exhibit immunological disorders, have a lower birth weight and display a shorter lifespan related to the expedited aging. In order to protect cow reproduction, the effects of heat stress at the intracellular and molecular levels should be tracked step by step, and the impacts of the dysregulation of thermal homeostasis (i.e., hyperthermy) should be taken into account.

Heat stress on cattle embryo: gene regulation and adaptation

Global warming has been affecting animal husbandry and farming production worldwide via changes in organisms and their habitats. In the tropics, these conditions are adverse for agriculture and animal production in some areas, due to high temperatures and relative humidity, affecting competitiveness related to economic activities. These environments have deteriorated livestock production, due to periods of drought, reduction in forage quality and heat stress, eliciting negative effects on reproduction, weight gain, and reduced meat and milk production. However, the use of animals adapted to tropics such as breeds derived from subspecies Bos primigenius indicus and native breeds from tropical countries or their crossings, is an alternative to improve production under high-temperature conditions. Therefore, physiological adaptation including gene expression induced by heat stress have been studied to understand the response of animals and to improve cross-breeding between cattle breeds to maintain high productivity in adverse weather conditions. Heat stress has been associated with lower reproductive performance in cows, due to the impact on blastocyst production, decreased implantation and increased embryonic death. Thus, for decades, in vitro fertilization and embryo transfer techniques have focused on studying the optimal conditions for production of high-quality embryos to transfer. The aim of this review is to discuss the effects of heat stress in bovine embryos, and their physiological and genetic modulation, focusing on the genes that are related with major adaptability to heat stress conditions and their relationship with different embryonic stages.

Thermoprotective molecules to improve oocyte competence under elevated temperature

Heat stress is an environmental factor that challenges livestock by disturbing animal homeostasis. Despite the broad detrimental effects of heat stress on reproductive function, the germline and the early preimplantation embryo are particularly prone. There is extensive evidence that elevated temperature reduces oocyte developmental competence through a series of cellular and molecular damages. Further research revealed that the oocyte respond to stress by activating cellular mechanisms such as heat shock response, unfolded protein response and autophagy to improve survival under heat shock. Such knowledge paved the way for the identification of thermoprotective molecules that alleviate heat-induced oocyte oxidative stress, organelle damage, and apoptosis. Therefore, this review depicts the deleterious effects of heat shock on oocyte developmental competence, heat-induced cellular and molecular changes, outlines pro-survival cellular mechanisms and explores thermoprotective molecules to improve oocyte competence.

Use of pregnancy-associated plasma protein-A during oocyte in vitro maturation increases IGF-1 and affects the transcriptional profile of cumulus cells and embryos from Nelore cows

Insulin-like growth factor 1 (IGF-1) activity is established by the regulation of IGF binding protein activity, which blocks IGF-1 functions, whereas pregnancy-associated plasma protein-A (PAPP-A) improves IGF-1 bioavailability and facilitates binding to IGF receptors. To further extend our understanding of the effect of exogenous PAPP-A on bovine embryo production, we added this protein during in vitro maturation of cumulus-oocyte complexes (COCs); moreover, we assessed its effects on IGF-1 quantity in the maturation medium, embryonic yield and postwarming survival, blastocyst quality, and transcript abundance. Bovine COCs were matured in a serum-free medium, either with PAPP-A supplementation (100 ng/ml) or without (control). The treatment group produced higher IGF-1 concentrations in the maturation medium; however, showed no difference on cleavage, blastocysts rates, and embryonic survival 3 and 24 hr postcryopreservation. Regarding gene expression, VNN1 was upregulated, whereas AGPAT9, FASN, EGFR, HAS2, and IMPDH1 were downregulated in PAPP-A treated. PAPP-A treated, CPT2, DNMT3A, and TFAM were upregulated, whereas ATF4 and IFITM3 were downregulated. We concluded that although the addition of PAPP-A did not affect embryo yield and blastocyst survival, higher IGF-1 levels may affect embryo competence through differential expression of genes involved in lipid metabolism, oocyte competence, and mitochondrial function.

Extracellular vesicles of follicular fluid from heat-stressed cows modify the gene expression of in vitro-matured oocytes

The effect of heat stress (HS) on cattle reproduction is deleterious with respect to ovarian follicular development and oocyte quality. The objective of this study was to investigate the effect of follicular fluid extracellular vesicles (EVs) obtained from cows maintained in thermoneutral (TN) or HS conditions on in vitro oocyte maturation. Nonlactating cows were estrous synchronized. Immediately after ovulation day (D1), the cows were randomly assigned to TN or HS environments. Follicular fluid from all follicles from each treatment was pooled, and EVs were obtained. Pools of 20 cumulus oocyte-complexes (COCs), were allocated to the following treatments: Control (n = 4 COC pools): matured in base medium; TN (n = 4 COC pools): matured in base medium supplemented with TN EV suspension; and HS (n = 4 COC pools): matured in base medium that was supplemented with the HS EV suspension. All treatments were conducted at 38.5 °C for 24 h in a humid atmosphere with 5% CO2. After maturation, the COCs were evaluated for meiotic progression, DNA integrity and oocyte quality-related gene expression. When the experimental groups were compared with the control group, a treatment effect was not observed for meiotic progression and DNA integrity. In the cumulus cells of TN group, there was relatively lesser expression of the IGFBP4 gene. In the oocytes of the TN as compared with the HS group, the IGFBP2, BMP15, GDF9, CDCA8, HAS2, RPL15, STAT3 and PFKP genes were expressed to a lesser extent. The findings indicated that oocytes matured in the presence of EVs from the follicular fluid of cows collected when there were TN conditions, however, there was a lesser expression of genes related to oocyte quality.

Signatures of selection and environmental adaptation across the goat genome post-domestication

BACKGROUND

Since goat was domesticated 10,000 years ago, many factors have contributed to the differentiation of goat breeds and these are classified mainly into two types: (i) adaptation to different breeding systems and/or purposes and (ii) adaptation to different environments. As a result, approximately 600 goat breeds have developed worldwide; they differ considerably from one another in terms of phenotypic characteristics and are adapted to a wide range of climatic conditions. In this work, we analyzed the AdaptMap goat dataset, which is composed of data from more than 3000 animals collected worldwide and genotyped with the CaprineSNP50 BeadChip. These animals were partitioned into groups based on geographical area, production uses, available records on solid coat color and environmental variables including the sampling geographical coordinates, to investigate the role of natural and/or artificial selection in shaping the genome of goat breeds.

RESULTS

Several signatures of selection on different chromosomal regions were detected across the different breeds, sub-geographical clusters, phenotypic and climatic groups. These regions contain genes that are involved in important biological processes, such as milk-, meat- or fiber-related production, coat color, glucose pathway, oxidative stress response, size, and circadian clock differences. Our results confirm previous findings in other species on adaptation to extreme environments and human purposes and provide new genes that could explain some of the differences between goat breeds according to their geographical distribution and adaptation to different environments.

CONCLUSIONS

These analyses of signatures of selection provide a comprehensive first picture of the global domestication process and adaptation of goat breeds and highlight possible genes that may have contributed to the differentiation of this species worldwide.

Genetic variation in resistance of the preimplantation bovine embryo to heat shock

Reproduction is among the physiological functions in mammals most susceptible to disruption by hyperthermia. Many of the effects of heat stress on function of the oocyte and embryo involve direct effects of elevated temperature (i.e. heat shock) on cellular function. Mammals limit the effects of heat shock by tightly regulating body temperature. This ability is genetically controlled: lines of domestic animals have been developed with superior ability to regulate body temperature during heat stress. Through experimentation in cattle, it is also evident that there is genetic variation in the resistance of cells to the deleterious effects of elevated temperature. Several breeds that were developed in hot climates, including Bos indicus (Brahman, Gir, Nelore and Sahiwal) and Bos taurus (Romosinuano and Senepol) are more resistant to the effects of elevated temperature on cellular function than breeds that evolved in cooler climates (Angus, Holstein and Jersey). Genetic differences are expressed in the preimplantation embryo by Day 4–5 of development (after embryonic genome activation). It is not clear whether genetic differences are expressed in cells in which transcription is repressed (oocytes >100 µm in diameter or embryos at stages before embryonic genome activation). The molecular basis for cellular thermotolerance has also not been established, although there is some suggestion for involvement of heat shock protein 90 and the insulin-like growth factor 1 system. Given the availability of genomic tools for genetic selection, identification of genes controlling cellular resistance to elevated temperature could be followed by progress in selection for those genes within the populations in which they exist. It could also be possible to introduce genes from thermotolerant breeds into thermally sensitive breeds. The ability to edit the genome makes it possible to design new genes that confer protection of cells from stresses like heat shock.