The landscape of circular RNAs and mRNAs in bovine milk exosomes

Unraveling the genetic basis of methane emission in dairy cattle: a comprehensive exploration and breeding approach to lower methane emissions

Ruminant animals, such as dairy cattle, produce CH4, which contributes to global warming emissions and reduces dietary energy for the cows. While the carbon foot print of milk production varies based on production systems, milk yield and farm management practices, enteric fermentation, and manure management are major contributors togreenhouse gas emissions from dairy cattle. Recent emerging evidence has revealed the existence of genetic variation for CH4 emission traits among dairy cattle, suggests their potential inclusion in breeding goals and genetic selection programs. Advancements in high-throughput sequencing technologies and analytical techniques have enabled the identification of potential metabolic biomarkers, candidate genes, and SNPs linked to methane emissions. Indeed, this review critically examines our current understanding of carbon foot print in milk production, major emission sources, rumen microbial community and enteric fermentation, and the genetic architecture of methane emission traits in dairy cattle. It also emphasizes important implications for breeding strategies aimed at halting methane emissions through selective breeding, microbiome driven breeding, breeding for feed efficiency, and breeding by gene editing.

Biomarkers of food intake and their relevance to metabolic syndrome

Metabolic syndrome (MetS) constitutes a prevalent risk factor associated with non communicable diseases such as cardiovascular disease and type 2 diabetes. A major factor impacting the etiology of MetS is diet. Dietary patterns and several individual food constituents have been related to the risk of developing MetS or have been proposed as adjuvant treatment. However, traditional methods of dietary assessment such as 24 h recalls rely greatly on intensive user-interaction and are subject to bias. Hence, more objective methods are required for unbiased dietary assessment and efficient prevention. While it is accepted that some dietary-derived constituents in blood plasma are indicators for certain dietary patterns, these may be too unstable (such as vitamin C as a marker for fruits/vegetables) or too broad (e.g. polyphenols for plant-based diets) or reflect too short-term intake only to allow for strong associations with prolonged intake of individual food groups. In the present manuscript, commonly employed biomarkers of intake including those related to specific food items (e.g. genistein for soybean or astaxanthin and EPA for fish intake) and novel emerging ones (e.g. stable isotopes for meat intake or microRNA for plant foods) are emphasized and their suitability as biomarker for food intake discussed. Promising alternatives to plasma measures (e.g. ethyl glucuronide in hair for ethanol intake) are also emphasized. As many biomarkers (i.e. secondary plant metabolites) are not limited to dietary assessment but are also capable of regulating e.g. anti-inflammatory and antioxidant pathways, special attention will be given to biomarkers presenting a double function to assess both dietary patterns and MetS risk.

Milk-derived small extracellular vesicles: a new perspective on dairy nutrition

Milk contains bioactive compounds that have multiple essential benefits. Milk-derived small extracellular vesicles (M-sEVs) have emerged as novel bioactive milk components with various beneficial biological functions and broad applications. The M-sEVs from different mammalian sources have similar composition and bioactive functions. The digestive stability and biocompatibility of the M-sEVs provide a good foundation for their physiological functions. Evidence suggests that M-sEVs promote intestinal, immune, bone, neural, liver, and heart health and show therapeutic effects against cancer, indicating their potential for use in functional foods. In addition, M-sEVs can be developed as natural delivery carriers owing to their superior structural characteristics. Further studies are needed to elucidate the relationship between the specific components and functions of M-sEVs, standardize their extraction processes, and refine relevant clinical trials to advance the future applications of M-sEVs. This review summarizes the structure and composition of M-sEVs isolated from different milk sources and discusses several common extraction methods. Since the introduction of M-sEVs for digestion and absorption, studies have been conducted on their biological functions. Furthermore, we outline the theoretical industrial production route, potential application scenarios of M-sEVs, and the future perspectives of M-sEV research.

The Characteristic Function of Blood-Derived Exosomes and Exosomal circRNAs Isolated from Dairy Cattle during the Dry Period and Mid-Lactation

Exosomes are key mediators of intercellular communication. They are secreted by most cells and contain a cargo of protein-coding genes, long noncoding RNAs (lncRNAs), and circular RNAs (circRNAs), which modulate recipient cell behavior. Herein, we collected blood samples from Holstein cows at days 30 (mid-lactation) and 250 (dry period) of pregnancy. Prolactin, follicle-stimulating hormone, luteinizing hormone, estrogen, and progesterone levels showed an obvious increase during D250. We then extracted exosomes from bovine blood samples and found that their sizes generally ranged from 100 to 200 nm. Further, Western blotting validated that they contained CD9, CD63, and TSG101, but not calnexin. Blood-derived exosomes significantly promoted the proliferation of mammary epithelial cells, particularly from D250. This change was accompanied by increased expression levels of proliferation marker proteins PCNA, cyclin D, and cyclin E, as detected by EdU assay, cell counting kit-8 assay, and flow cytometric cell cycle analysis. Moreover, we treated mammary epithelial cells with blood-derived exosomes that were isolated from the D30 and D250 periods. And RNA-seq of two groups of cells led to the identification of 839 differentially expressed genes that were significantly enriched in KEGG signaling pathways associated with apoptosis, cell cycle and proliferation. In bovine blood-derived exosomes, we found 12,747 protein-coding genes, 31,181 lncRNAs, 9374 transcripts of uncertain coding potential (TUCP) candidates, and 460 circRNAs, and 32 protein-coding genes, 806 lncRNAs, 515 TUCP candidates, and 45 circRNAs that were differentially expressed between the D30 and D250 groups. We selected six highly expressed and four differentially expressed circRNAs to verify their head-to-tail splicing using PCR and Sanger sequencing. To summarize, our findings improve our understanding of the key roles of blood-derived exosomes and the characterization of exosomal circRNAs in mammary gland development.

Multifunctional Milk-Derived Small Extracellular Vesicles and Their Biomedical Applications

In recent years, small extracellular vesicles (sEVs) have been regarded as the next generation of novel delivery systems after lipid nanoparticles because of their advantages and huge prospects in drug delivery. Studies have shown that sEVs are abundant in milk and therefore can be a large and economical source of sEVs. Natural milk-derived small extracellular vesicles (msEVs) have important functions such as immune regulation, anti-bacterial infection, anti-oxidative, etc., and play a beneficial role in human health at multiple levels, including intestinal health, bone/muscle metabolism, and microbiota regulation. In addition, because they can pass the gastrointestinal barrier and have low immunogenicity, good biocompatibility, and stability, msEVs are considered a crucial oral drug delivery vehicle. Moreover, msEVs can be further engineered for targeted delivery to prolong the circulation time or enhance local drug concentrations. However, msEVs separation and purification, complex contents, and quality control hinder their application in drug delivery. This paper provides a comprehensive review of the biogenesis and characteristics, isolation and purification, composition, loading methods, and function of msEVs, based on which their applications in biomedical fields are further explored.

Emerging Roles of Noncoding RNAs in Bovine Mastitis Diseases

Non-coding RNAs (ncRNAs) are an abundant class of RNA with varying nucleotide lengths. They have been shown to have great potential in eutherians/human disease diagnosis and treatments and are now gaining more importance for the improvement of diseases in livestock. To date, thousands of ncRNAs have been discovered in the bovine genome and the continuous advancement in deep sequencing technologies and various bioinformatics tools has enabled the elucidation of their roles in bovine health. Among farm animals' diseases, mastitis, a common inflammatory disease in cattle, has caused devastating economic losses to dairy farmers over the last few decades. Here, we summarize the biology of bovine mastitis and comprehensively discuss the roles of ncRNAs in different types of mastitis infection. Based on our findings and relevant literature, we highlighted various evidence of ncRNA roles in mastitis. Different approaches (in vivo versus in vitro) for exploring ncRNA roles in mastitis are emphasized. More particularly, the potential applications of emerging genome editing technologies, as well as integrated omics platforms for ncRNA studies and implications for mastitis are presented.

Beneficial Effects of Bovine Milk Exosomes in Metabolic Interorgan Cross-Talk

Extracellular vesicles are membrane-enclosed secreted vesicles involved in cell-to-cell communication processes, identified in virtually all body fluids. Among extracellular vesicles, exosomes have gained increasing attention in recent years as they have unique biological origins and deliver different cargos, such as nucleic acids, proteins, and lipids, which might mediate various health processes. In particular, milk-derived exosomes are proposed as bioactive compounds of breast milk, which have been reported to resist gastric digestion and reach systemic circulation, thus being bioavailable after oral intake. In the present manuscript, we critically discuss the available evidence on the health benefits attributed to milk exosomes, and we provide an outlook for the potential future uses of these compounds. The use of milk exosomes as bioactive ingredients represents a novel avenue to explore in the context of human nutrition, and they might exert important beneficial effects at multiple levels, including but not limited to intestinal health, bone and muscle metabolism, immunity, modulation of the microbiota, growth, and development.

Non-Coding RNAs in Human Breast Milk: A Systematic Review

Breast milk is the primary source of nutrition and hydration for the newborn infant but also plays an important role in the child’s first immune defense. Additionally, several breast milk factors have been implicated in immune-related health outcomes later in life, including immunoglobulins, cytokines, chemokines, growth factors and, more recently, non-coding RNA (ncRNA) species. In this systematic review, we provide a comprehensive summary of the current literature on endogenous ncRNAs found in human breast milk. Thirty (30) relevant studies were identified and, whilst the majority studies focused on microRNAs (miRNAs), there is evidence that breast milk contains high quantities of RNA which also include long-coding RNAs, circular RNAs, as well as other short RNAs and fragmented tRNA and rRNAs. Among studies investigating miRNAs, miR-148a-3p, miR-30a/d-5p, miR-22-3p, miR-146b-5p, miR-200a/c-3p, and the 5p end of the let-7 miRNAs were commonly reported among the top 10 miRNAs in the cell, lipid, and skim milk fractions of breast milk. Methodological difference and small sample sizes limit the possibility of conclusively identifying which maternal and infant characteristics affect the miRNA profile. The highly expressed miRNAs were generally reported to be similar across lactational stage, milk fraction, maternal and infant characteristics, or infant growth and health. All the same, individual studies identify potential differences in miRNA expression levels which should be confirmed by future studies. Stability, uptake, and physiological functions of miRNAs were also considered in several studies. Breast milk miRNAs are relatively resistant to a range of harsh conditions and uptake experiments suggest that extracellular vesicles containing miRNAs and circular RNAs can be taken up by intestinal epithelial cells. Although the evidence regarding the functional effect of breast milk miRNAs is limited, the predicted functions range from metabolic and biosynthetic processes to signaling pathways, cellular adhesion, communication, growth, and differentiation. Finally, this systematic review highlights some of the methodological challenges and knowledge gaps which can help direct future research in this field. In particular, it is important to further investigate the bioavailability of miRNAs in different milk fractions, and to characterize other ncRNAs which are largely unstudied.

Construction and evaluation of liraglutide delivery system based on milk exosomes: a new idea for oral peptide delivery

BACKGROUND

Increasing the bioavailability of peptide or protein drugs has always been an essential topic in pharmacy. Milk exosomes as a carrier for oral drug delivery systems have begun to attract attention in recent years. The application of oral milk exosomes carriers to peptide drugs such as liraglutide is worth trying.

OBJECTIVE

Milk-derived exosomes are used in this study to encapsulate the GLP-1 receptor agonist liraglutide. It also explored the feasibility of using this drug delivery system for oral biomolecules delivery in the future.

METHODS

The size and morphology of milk exosomes were characterized. The gastrointestinal stability of milk exosomes was evaluated in a dialysis bag. The cellular uptake of milk exosomes in an intestinal cell was observed. Six drug loading methods have been evaluated and compared preliminarily, and they are the incubation method, sonication method, extrusion method, freeze-thaw cycles method, saponin-assisted method, and electroporation method.

RESULTS

As demonstrated in this study, milk exosomes showed significant stability in the gastrointestinal environment and excellent affinity with intestinal cells, indicating their unique benefits used for oral drug delivery. Effective drug loading method for exosomes is challenging. Among the six drug loading methods used in this study, the liraglutide-Exo prepared by the extrusion method obtained the most significant drug load, which was 2.45 times the direct incubation method. The liraglutide-Exo obtained by the freeze-thaw cycles method has the slightest morphological change.

CONCLUSION

The study showed milk exosome-based oral drug delivery systems are promising.

Characterization and comparative analysis of transcriptional profiles of porcine colostrum and mature milk at different parities

BACKGROUND

Porcine milk is a complex fluid, containing a myriad of immunological, biochemical, and cellular components, made to satisfy the nutritional requirements of the neonate. Whole milk contains many different cell types, including mammary epithelial cells, neutrophils, macrophages, and lymphocytes, as well nanoparticles, such as milk exosomes. To-date, only a limited number of livestock transcriptomic studies have reported sequencing of milk. Moreover, those studies focused only on sequencing somatic cells as a proxy for the mammary gland with the goal of investigating differences in the lactation process. Recent studies have indicated that RNA originating from multiple cell types present in milk can withstand harsh environments, such as the digestive system, and transmit regulatory molecules from maternal to neonate. Transcriptomic profiling of porcine whole milk, which is reflective of the combined cell populations, could help elucidate these mechanisms. To this end, total RNA from colostrum and mature milk samples were sequenced from 65 sows at differing parities. A stringent bioinformatic pipeline was used to identify and characterize 70,841 transcripts.

RESULTS

The 70,841 identified transcripts included 42,733 previously annotated transcripts and 28,108 novel transcripts. Differential gene expression analysis was conducted using a generalized linear model coupled with the Lancaster method for P-value aggregation across transcripts. In total, 1667 differentially expressed genes (DEG) were identified for the milk type main effect, and 33 DEG were identified for the milk type x parity interaction. Several gene ontology (GO) terms related to immune response were significant for the milk type main effect, supporting the well-known fact that immunoglobulins and immune cells are transferred to the neonate via colostrum.

CONCLUSIONS

This is the first study to perform global transcriptome analysis from whole milk samples in sows from different parities. Our results provide important information and insight into synthesis of milk proteins and innate immunity and potential targets for future improvement of swine lactation and piglet development.

Biological Properties of Milk-Derived Extracellular Vesicles and Their Physiological Functions in Infant

Extracellular vesicles (EVs) are released by all cells under pathological and physiological conditions. EVs harbor various biomolecules, including protein, lipid, non-coding RNA, messenger RNA, and DNA. In 2007, mRNA and microRNA (miRNA) carried by EVs were found to have regulatory functions in recipient cells. The biological function of EVs has since then increasingly drawn interest. Breast milk, as the most important nutritional source for infants, contains EVs in large quantities. An increasing number of studies have provided the basis for the hypothesis associated with information transmission between mothers and infants via breast milk-derived EVs. Most studies on milk-derived EVs currently focus on miRNAs. Milk-derived EVs contain diverse miRNAs, which remain stable both in vivo and in vitro; as such, they can be absorbed across different species. Further studies have confirmed that miRNAs derived from milk-derived EVs can resist the acidic environment and enzymatic hydrolysis of the digestive tract; moreover, they can be absorbed by intestinal cells in infants to perform physiological functions. miRNAs derived from milk EVs have been reported in the maturation of immune cells, regulation of immune response, formation of neuronal synapses, and development of metabolic diseases such as obesity and diabetes. This article reviews current status and advances in milk-derived EVs, including their history, biogenesis, molecular contents, and biological functions. The effects of milk-derived EVs on growth and development in both infants and adults were emphasized. Finally, the potential application and future challenges of milk-derived EVs were discussed, providing comprehensive understanding and new insight into milk-derived EVs.

Circular RNA as a Potential Biomarker for Melanoma: A Systematic Review

Circular RNAs (circRNAs) are newly discovered RNAs with covalently looped structures. Due to their resistance to RNAase degradation and tissue-specific expression, circRNAs are expected to be potential biomarkers in early diagnosis and target treatment of many diseases. However, the role of circRNAs in melanoma still needs to be systematically reviewed for better understanding and further research. Based on published articles in PubMed, Embase, Cochrane Library, and Web of Science database, we systematically reviewed the implications and recent advances of circRNAs in melanoma, focusing on function, mechanism, and correlation with melanoma progression. According to inclusion and exclusion criteria, a total of 19 articles were finally included in this systematic review. Of the 19 studies, 17 used human samples, including melanoma tissues (n = 16) and blood serum of patients with melanoma (n = 1). The sample size of the study group ranged from 20 to 105 based on the reported data. Several studies explored the association between circRNAs and clinicopathological characteristics. circRNA dysregulation was commonly observed in melanoma patients. circRNAs function in melanoma by miRNA sponging and interaction with RNA binding proteins (RBP), ultimately controlling several important signaling pathways and cancer-related cellular processes, including proliferation, migration, invasion, metastasis, apoptosis, and glucose metabolism. circRNA expression could be associated with prognostic factors and drug responses, consolidating the potential clinical value in melanoma. Herein, we clarified the functional, prognostic, and predictive roles of circRNAs in melanoma in this systematic review, providing future directions for studies on melanoma-associated circRNAs.

Noncoding RNAs: Regulatory Molecules of Host-Microbiome Crosstalk

Recent emerging evidence has revealed that regulatory noncoding RNAs (microRNAs, circular RNAs) modulate host-microbe interactions and they have been proposed as potential biomarkers of the host's response to microbiome-linked pathologies such as cancers, obesity, and neurodegenerative diseases. Interactions between microRNAs and circular RNAs, however, increase the complexity of the mechanisms that modulate host-microbe interactions. Current knowledge on these noncoding RNAs (ncRNAs) is mainly generated from well controlled germ-free or knockout (small) animal models. Application of such knowledge to effective modulation outcomes in humans (and livestock) is challenging due to the complex nature of microbiome-linked pathologies in larger outbred animals that constantly interact with the changing environment. This review critically discusses the findings of regulatory noncoding RNAs and their roles in microbiome-linked pathologies in small and large animals and provides insights on their roles as potential therapeutic agents to improve human (and livestock) health.

Biological Characteristics and Roles of Noncoding RNAs in Milk-Derived Extracellular Vesicles

Extracellular vesicles (EVs) have diverse roles in the transport of proteins, lipids, and nucleic acids between cells, and they serve as mediators of intercellular communication. Noncoding RNAs (ncRNAs) that are present in EVs, including microRNAs, long noncoding RNAs, and circular RNAs, have been found to participate in complex networks of interactions and regulate a wide variety of genes in animals. Milk is an important source of nutrition for humans and other mammals. Evidence suggests that milk-derived EVs contain abundant ncRNAs, which are stable and can be transported to the offspring and other consumers. Current data suggest a strong link between milk EV ncRNAs and many biological processes, and these ncRNAs have been drawing increasing attention and might play an epigenetic regulatory role in recipients, though further research is still necessary to understand their precise roles. The present review introduces basic information about milk EV ncRNAs, summarizes their expression profiles, biological characteristics, and functions based on current knowledge, and discusses their biological roles, indeterminate issues, and perspectives. Our goal is to provide a deeper understanding of the physiological effects of milk EV ncRNAs on offspring and to provide a reference for future research in this field.

Exploration of Long Non-coding RNAs and Circular RNAs in Porcine Milk Exosomes

RNA in milk exosomes can be absorbed in the mammalian intestinal tract and function in gene expression regulations. Our previous work demonstrated that porcine milk exosomes (PME) contain large amounts of miRNAs and mRNAs. Increasing evidence suggests that long non-coding RNAs (lncRNAs) and circular RNAs (circRNAs) are of particular interest, given their key role in diverse biological processes of animals. However, the expression profiles and the potential functions of lncRNAs and circRNAs in PME are still unknown. In the present study, we isolated PME by ultracentrifugation and performed a comprehensive analysis of lncRNA and circRNA in PME by using RNA sequencing. As a result, 2,466 novel lncRNAs, 809 annotated lncRNAs, and 61 circRNAs were identified in PME. The lncRNAs shared similar characteristics with other mammals in terms of length, exon number, and open reading frames. However, lncRNAs showed a higher level compared with mRNAs. Eight lncRNAs and five circRNAs in PME were selected for PCR identification. A functional enrichment analysis on the target genes of lncRNAs indicated that these genes were involved in cellular macromolecule metabolic, RNA metabolic, and immune processes. The circRNAs host genes were enriched in nucleic acid binding and adherence junction. We also evaluated the potential interaction targets between miRNAs and PME lncRNAs or circRNAs, and the results showed that the PME lncRNAs and the circRNAs have a high density of miRNA target sites. The top 20 highly expressed lncRNAs were found to interact with the proliferation-related miRNAs, and the circRNAs potentially targeted many miRNAs that are associated with the intestinal barrier. This study is the first to provide a resource for lncRNA and circRNA research of porcine milk. Moreover, the potential interaction between lncRNA/circRNA and miRNA is revealed. The present study expands our knowledge of non-coding RNAs in milk, and additional research is necessary to confirm their exactly physiological functions.

Identification of circRNA-Associated-ceRNA Networks Involved in Milk Fat Metabolism under Heat Stress

Summer temperatures are generally high in Southern China, and cows are likely to suffer a heat stress reaction. Heat stress will have a negative impact on the performance of dairy cows; however, the mechanism by which high temperature affects lactation is not clear. CircRNA is a type of non-coding RNA discovered in recent years, which performs a crucial function in many biological activities. However, the effects of circRNA on lactation function of dairy cows under heat stress is unknown. The present study aimed to explore the expression levels of circRNA in the mammary gland tissue of cows under heat stress. Firstly, we collected blood and milk samples of summer and winter cows and evaluated lactation performance using serum indicators, milk production, and milk composition. Incorporating the calculation of the temperature and humidity index, we conformed the heat stress status of cows in summer. Heat stress increased the concentration of HSP70 and decreased the concentration of SOD and PRL. Heat stress not only reduced milk yield but also affected milk quality, with milk lactose and milk protein decreasing with increased temperature. The analysis of the fatty acid composition in summer milk found significantly reduced concentrations of unsaturated fatty acids, especially long-chain unsaturated fatty acids. Sequencing of the cow's mammary gland transcriptome revealed that compared to the appropriate temperature (ST) group, the heat stress (HS) group had a total of 2204 upregulated and 3501 downregulated transcripts. GO enrichment and KEGG pathway analysis showed that these genes were mainly related to milk fat metabolism. In addition, 19 upregulated and 19 downregulated circRNA candidates were found in response to heat stress. We used Pearson's test to establish the correlation of circRNA-mRNA and identified four pairs of circRNA-miRNA networks between four circRNAs, six miRNAs, and the CD36 gene. In this study, we revealed the possible role of circRNAs in lactation of dairy cows and identified that circRNA-miRNA-mRNA networks might exist in the cow's mammary glands, providing valuable experience for dairy lactation and milk quality.

Emerging Roles of Heat-Induced circRNAs Related to Lactogenesis in Lactating Sows

Heat stress negatively influences milk production and disrupts normal physiological activity of lactating sows, but the precious mechanisms by which hyperthermia adversely affects milk synthesis in sows still remain for further study. Circular RNAs are a novel class of non-coding RNAs with regulatory functions in various physiological and pathological processes. The expression profiles and functions of circRNAs of sows in lactogenesis remain largely unknown. In the present study, long-term heat stress (HS) resulted in a greater concentration of serum HSP70, LDH, and IgG, as well as decreased levels of COR, SOD, and PRL. HS reduced the total solids, fat, and lactose of sow milk, and HS significantly depressed CSNαs1, CSNαs2, and CSNκ biosynthesis. Transcriptome sequencing of lactating porcine mammary glands identified 42 upregulated and 25 downregulated transcripts in HS vs. control. Functional annotation of these differentially-expressed transcripts revealed four heat-induced genes involved in lactation. Moreover, 29 upregulated and 21 downregulated circRNA candidates were found in response to HS. Forty-two positively correlated circRNA-mRNA expression patterns were constructed between the four lactogenic genes and differentially expressed circRNAs. Five circRNA-miRNA-mRNA post-transcriptional networks were identified involving genes in the HS response of lactating sows. In this study we establish a valuable resource for circRNA biology in sow lactation. Analysis of a circRNA-miRNA-mRNA network further uncovered a novel layer of post-transcriptional regulation that could be used to improve sow milk production.

Circular RNA; a new biomarker for breast cancer: A systematic review

Circular RNAs (circRNAs) were recently discovered as a looped subset of competing endogenous RNAs, with an ability to regulate gene expression by microRNA sponging. There are several studies on their potential roles in cancer development, such as colorectal cancer and basal cell carcinoma. However, there is still a significant gap in the knowledge about circRNA functions in breast cancer (BC) progression. The current study systematically reviewed circRNA biogenesis and their potential roles as a novel biomarker in BC on published studies of the MEDLINE®/PubMed, Cochrane®, and Scopus® databases. The obtained results showed a general dysregulation of circRNAs expression in BC cells with a cell-type and stage-specific manner. The potential connection between circRNAs and BC cell proliferation, apoptosis, metastasis, and chemotherapy sensitivity and resistance were discussed.