Bos Grunniens Research Articles

Shrub coverage alters the rumen bacterial community of yaks (Bos grunniens) grazing in alpine meadows.

Proliferation of shrubs at the expense of native forage in pastures has been associated with large changes in dry-matter intake and dietary components for grazing ruminants. These changes can also affect the animals’ physiology and metabolism. However, little information is available concerning the effect of pastoral-shrub grazing on the rumen bacterial community. To explore rumen bacteria composition in grazing yaks and the response of rumen bacteria to increasing shrub coverage in alpine meadows, 48 yak steers were randomly assigned to four pastures with shrub coverage of 0%, 5.4%, 11.3%, and 20.1% (referred as control, low, middle, and high, respectively), and ruminal fluid was collected from four yaks from each pasture group after 85 days. Rumen fermentation products were measured and microbiota composition determined using Ion S5TM XL sequencing of the 16S rRNA gene. Principal coordinates analysis (PCoA) and similarity analysis indicated that the degree of shrub coverage correlated with altered rumen bacterial composition of yaks grazing in alpine shrub meadows. At the phyla level, the relative abundance of Firmicutes in rumen increased with increasing shrub coverage, whereas the proportions of Bacteroidetes, Cyanobacteria and Verrucomicrobia decreased. Yaks grazing in the high shrub-coverage pasture had decreased species of the genus Prevotellaceae UCG-001, Lachnospiraceae XPB1014 group, Lachnospiraceae AC2044 group, Lachnospiraceae FCS020 group and Fretibacterium, but increased species of Christensenellaceae R-7 group, Ruminococcaceae NK4A214 group, Ruminococcus 1, Ruminococcaceae UCG-002, Ruminococcaceae UCG-005 and Lachnospiraceae UCG-008. These variations can enhance the animals’ utilization efficiencies of cellulose and hemicellulose from native forage. Meanwhile, yaks grazed in the high shrub-coverage pasture had increased concentrations of ammonia nitrogen (NH3-N) and branched-chain volatile fatty acids (isobutyrate and isovalerate) in rumen compared with yaks grazing in the pasture without shrubs. These results indicate that yaks grazing in a high shrub-coverage pasture may have improved dietary energy utilization and enhanced resistance to cold stress during the winter. Our findings provide evidence for the influence of shrub coverage on the rumen bacterial community of yaks grazing in alpine meadows as well as insights into the sustainable production of grazing yaks on lands with increasing shrub coverage on the Qinghai-Tibet Plateau.

Detection of Theileria spp. in ticks, sheep keds (Melophagus ovinus), and livestock in the eastern Tibetan Plateau, China.

Theileria species, with a broad geographic distribution, infect a wide range of both domestic and wild animals and are transmitted by ixodid ticks. Currently, there is no comprehensive report regarding the distribution of Theileria spp. in the eastern Tibetan Plateau, especially in Ganze Tibetan autonomous prefecture (153,700km2) and Ngawa Tibetan and Qiang autonomous prefecture (84,242km2) of Sichuan province, China. In this study, we collected blood samples from yaks (n = 144) (Bos grunniens), Tibetan sheep (n = 92), and Tibet horses (n = 142) in Ganze and Ngawa.Theileria sinensis, T. luwenshuni, and T. equi were the dominant Theileria species detected in yaks, Tibetan sheep, and horses with the total infection rates of 25.7% (37/144), 75.0% (69/92), and 51.4% (73/142), respectively. For ectoparasites, T. luwenshuni was the only Theileria species detected in sheep keds (Melophagus ovinus) with an infection rate of 30.8% (8/26). The total infection rates of T. sinensis in Haemaphysalis qinghaiensis, Dermacentor everestianus, and Rhipicephalus microplus were 34.6% (36/104), 34.0% (17/50), and 51.3% (58/113), respectively. Theileria spp., belonging to T. sergenti/buffeli/orientalis group, were only detected in R. microplus collected in Danba county of Ganze with a total infection rate of 39.9% (19/48). Our results provide important data of the epidemiology of Theileria spp. in livestock and ectoparasites and will assist with the implementation of measures to control theileriosis transmission in eastern Tibetan Plateau, China.

Molecular characterization of tick-borne bacteria and protozoans in yaks (Bos grunniens), Tibetan sheep (Ovis aries) and Bactrian camels (Camelus bactrianus) in the Qinghai-Tibetan Plateau Area, China

Due to the specific plateau climate, a variety of unique animals live in the Qinghai-Tibetan Plateau Area (QTPA) including yaks (Bos grunniens), Tibetan sheep (Ovis aries) and Bactrian camels (Camelus bactrianus). However, information on tick-borne diseases (TBDs) in the QTPA and on the molecular characteristics of tick-borne pathogens (TBPs) in the area is limited. Therefore, the aim of this study was to investigate Anaplasma spp., Babesia spp., Theileria spp., Borrelia burgdorferi sensu lato and Rickettsia spp. infecting yaks, Tibetan sheep and camels in this area. A total of 276 animals were screened. Overall, 84.5% (164/194) of yaks, 58% (23/40) of Tibetan sheep, and 38% (16/42) of camels tested positive for at least one pathogen. Theileria spp., Anaplasma ovis and spotted fever group (SFG) Rickettsia spp. were detected as TBPs in the current study with overall infection rates of 10.9% (30/276), 8.3% (23/276) and 62.9% (171/276), respectively. Further study revealed that 1.5% (3/194) of the yaks were infected with Theileria sp. OT3, 1.5% (3/194) with T. luwenshuni, 6.2% (12/194) with T. uilenbergi, 1.1% (2/194) with T. ovis and 82% (159/194) with SFG Rickettsia spp. It was also shown that 58% (23/40) of the Tibetan sheep were infected with A. ovis and 15% (6/40) with T. ovis. Among the camels, 10% (4/42) were infected with T. equi, while 29% (12/42) were positive for Rickettsia spp. Sequence analysis revealed that the Rickettsia spp. infecting yaks and camels were Rickettsia raoultii and Rickettsia slovaca. To the best of our knowledge, this study reports the first detection and characterization of these pathogens in yaks, Tibetan sheep and camels in the country, except for T. luwenshuni infections in yaks.

Expression characteristics of immune factors in secondary lymphoid organs of newborn, juvenile and adult yaks (Bos grunniens)

Little is known about lymphoid organ development in yaks. In this study, we characterize and evaluate the main markers of T cell, B cell, plasma cell and antigen-presenting cell in the mesenteric lymph nodes, spleen and hemal node in newborn, juvenile and adult yaks by immunohistochemistry, real-time quantitative polymerase chain reaction and western blotting. The structures of all organs were not fully developed in newborn. The CD3+ cells were mainly located in the paracortex area of the mesenteric lymph node and the T cell dependent area in the hemal node and spleen. CD79a+ cells were mainly detected in the lymphoid follicles. The expression of CD3 and CD79a increased from newborn to juvenile and then decreased in adults. The expression of CD3 was always higher in the spleen and CD79a was higher in the mesenteric lymph node. IgG+ and IgA+ cells were observed in all examined samples, except in newborn yak hemal node. IgG and IgA were up-regulated with age and the highest expression was observed in the mesenteric lymph node. The SIRPα and CD68 were widely expressed. A significant feature was that the SIRPα expression in the spleen was lowest in newborns but highest in juvenile and adult yaks. The expression of CD68 in the hemal node was highest in all groups and increased from newborn to adult yaks. This study sheds light on the relationship between the morphology and function of these organs and provides useful references for normal yak lymphoid organ development.

Effects of Dietary Energy Levels on Rumen Fermentation, Microbial Diversity, and Feed Efficiency of Yaks (Bos grunniens)

The microbial community of the yak (Bos grunniens) rumen plays an important role in surviving the harsh Tibetan environment where seasonal dynamic changes in pasture cause nutrient supply imbalances, resulting in weight loss in yaks during the cold season. A better understanding of rumen microbiota under different feeding regimes is critical for exploiting the microbiota to enhance feed efficiency and growth performance. This study explored the impact of different dietary energy levels on feed efficiency, rumen fermentation, bacterial community, and abundance of volatile fatty acid (VFA) transporter transcripts in the rumen epithelium of yaks. Fifteen healthy castrated male yaks were divided into three groups and fed with low (YL), medium (YM), and high energy (YH) levels diet having different NEg of 5.5, 6.2, and 6.9 MJ/kg, respectively. The increase in feed efficiency was recorded with an increase in dietary energy levels. The increase in dietary energy levels decreased the pH and increased the concentrations of acetate, propionate, butyrate, and valerate in yak rumens. The increase in the mRNA abundance of VFA transporter genes (MCT1, DRA, PAT1, and AE2) in the rumen epithelium of yaks was recorded as dietary energy level increased. High relative abundances of Firmicutes and Bacteroidetes were recorded with the increase in dietary energy levels. Significant population shifts at the genus level were recorded among the three treatments. This study provides new insights into the dietary energy-derived variations in rumen microbial community.

The whole-transcriptome landscape of muscle and adipose tissues reveals the ceRNA regulation network related to intramuscular fat deposition in yak

BackgroundThe Intramuscular fat (IMF) content in meat products, which is positively correlated with meat quality, is an important trait considered by consumers. The regulation of IMF deposition is species specific. However, the IMF-deposition-related mRNA and non-coding RNA and their regulatory network in yak (Bos grunniens) remain unknown. High-throughput sequencing technology provides a powerful approach for analyzing the association between transcriptome-related differences and specific traits in animals. Thus, the whole transcriptomes of yak muscle and adipose tissues were screened and analyzed to elucidate the IMF deposition-related genes. The muscle tissues were used for IMF content measurements.ResultsSignificant differences were observed between the 0.5- and 2.5-year-old yaks. Several mRNAs, miRNAs, lncRNAs and circRNAs were generally expressed in both muscle and adipose tissues. Between the 0.5- and 2.5-year-old yaks, 149 mRNAs, 62 miRNAs, 4 lncRNAs, and 223 circRNAs were differentially expressed in muscle tissue, and 72 mRNAs, 15 miRNAs, 9 lncRNAs, and 211 circRNAs were differentially expressed in adipose tissue. KEGG annotation revelved that these differentially expressed genes were related to pathways that maintain normal biological functions of muscle and adipose tissues. Moreover, 16 mRNAs, 5 miRNAs, 3 lncRNAs, and 5 circRNAs were co-differentially expressed in both types of tissue. We suspected that these co-differentially expressed genes were involved in IMF-deposition in the yak. Additionally, LPL, ACADL, SCD, and FASN, which were previously shown to be associated with the IMF content, were identified in the competing endogenous RNA (ceRNA) regulatory network that was constructed on the basis of the IMF deposition-related genes. Three ceRNA subnetworks also revealed that TCONS-00016416 and its target SIRT1 “talk” to each other through the same miR-381-y and miR-208 response elements, whereas TCONS-00061798 and its target PRKCA, and TCONS-00084092 and its target LPL “talk” to each other through miR-122-x and miR-499-y response elements, respectively.ConclusionTaken together, our results reveal the potential mRNA and noncoding RNAs involved in IMF deposition in the yak, providing a useful resource for further research on IMF deposition in this animal species.

Valorization of Yak (Bos grunniens) Bones as Sources of Functional Ingredients

Yak (Bos grunniens) bone, is an underutilized biowaste that is generated as a major byproduct from yak slaughtering process. More commonly, yak bones are either made into primary processing products like whole bone powder or simply disposed, which may not only cause resources waste but also produce pressure on the sensitive and frail environment in cold plateau areas. The aim of this study was to valorize yak bone biowastes to functional ingredients while simultaneously reduce the adverse impact of yak bone biowastes discharge on plateau fragile ecological environment. Sequential purification of yak bone collagen hydrolysates was achieved by ultrafiltration, size exclusion chromatography (SEC), semi-preparative reverse phase high-performance liquid chromatography (RP-HPLC) and HPLC coupled to electrospray ionization tandem mass spectrometry (ESI–MS/MS). The bioactivity of the peptides on MC3T3-E1 osteoblast proliferation was evaluated in vitro by MTT method. Furthermore, the most potent peptide was selected and its underlying molecular mechanism was investigated through molecular docking simulation using the software of Discovery Studio 2018. 35 novel peptides were identified by mass spectrometry analysis, of which 9 were chemically synthesized and evaluated for the osteoblast proliferation-promoting activity. At a concentration of 0.05 mg/mL, peptide GPAGPPGPIGNV displayed the highest osteoblast proliferation-promoting activity with an increase of 42.7% in cell growth. Molecular docking study revealed that the main interactions of GPAGPPGPIGNV with epidermal growth factor receptor were the van der waals and hydrogen bonding. These results suggest that yak bones-derived peptides could be potentially used as osteogenic ingredients in functional foods. This work provides a feasible strategy for valorization of yak bone biowastes and sustainable development of animal husbandry industry in Qinghai-Tibetan Plateau. This work provides a feasible strategy for valorization of yak bone biowastes and sustainable development of animal husbandry industry in Qinghai-Tibetan Plateau.

Genome-Wide Analysis Reveals Changes in Polled Yak Long Non-coding RNAs in Skeletal Muscle Development.

Long non-coding RNAs (lncRNAs) have been extensively studied in recent years. Numerous lncRNAs have been identified in mice, rats, and humans, some of which play important roles in muscle formation and development. However, little is known about lncRNA regulators that affect muscle development in yak (Bos grunniens). LncRNA expression during skeletal muscle development in yak was analyzed by RNA sequencing at three development stages: 3 years (group A), 6 months (group M), and 90-day-old fetuses (group E). A total of 1180 lncRNAs were identified in the three development stages. Compared with group E, 154 were upregulated and 130 were downregulated in group A. Compared with group A, 31 were upregulated and 29 were downregulated in group M. Compared with group E, 147 were upregulated and 149 were downregulated in group M (padj < 0.001, |log2FC| > 1.2). In addition, functional annotation analysis based on gene ontology (GO) and the Kyoto protocol encyclopedia of genes and genomes (KEGG) database showed that differentially expressed lncRNAs (DElncRNAs) were cis–trans target genes. The results showed that DElncRNAs were mainly involved in PI3K-Akt signaling pathway, focal adhesion, MAPK signaling pathway, apoptosis, and p53 signaling pathway. Furthermore, RTL1, IGF2, MEF2C, Pax7, and other well-known muscle development regulators were included in a co-expression network of differentially expressed target genes and lncRNAs. These data will help to further clarify the function of lncRNAs in the different stages of skeletal muscle developmental in yak.

An Untargeted Metabolomics Investigation of Jiulong Yak (Bos grunniens) Meat by 1H-NMR.

Yak represents the main meat source for Tibetan people. This work aimed to investigate the metabolome of raw meat from Jiulong yaks, focusing on specimens farmed and harvested locally through traditional procedures. Untargeted nuclear magnetic resonance spectroscopy (1H-NMR) was selected as the analytical platform. Samples from longissimus thoracis, trapezius, triceps brachii and biceps femoris muscles, with different prevalences of red and white fibers, were selected. Among the fifty-three metabolites quantified in each of them, carnitine, carnosine, creatine and taurine are known for their bioactive properties. Twelve molecules were found to be differently concentrated in relation to muscle type. Longissimus thoracis, compared to biceps femoris, had higher concentrations of carnosine and formate and lower concentrations of mannose, inosine, threonine, IMP, alanine, valine, isoleucine, tyrosine, phenylalanine and leucine. A metabolic pathway analysis suggested that the main pathways differing among the muscles were connected to the turnover of amino acids. These results contribute to a deeper understanding of yak raw meat metabolism and muscle type differences, which can be used as an initial reference for the meat industry to set up muscle-specific investigations. The possibility of simultaneously quantifying several bioactive compounds suggests that these investigations could revolve around meat’s nutritional value.

CircRNA Expression Profile during Yak Adipocyte Differentiation and Screen Potential circRNAs for Adipocyte Differentiation.

The yak (Bos grunniens) is subjected to nutritional deficiency during the whole winter grazing season; deciphering the adipose metabolism and energy homeostasis under cold and nutrients stress conditions could be a novel way to understand the specific mechanism of energy metabolism. Circular RNAs (circRNAs) have elucidated that they play a key role in many biological events, but the regulatory function of adipose development remains mostly unknown. Therefore, the expression pattern of circRNAs were identified for the first time during yak adipocyte differentiation to gain insight into their potential functional involvement in bovine adipogenesis. We detected 7203 circRNA candidates, most of them contained at least two exons, and multiple circRNA isoforms could be generated from one parental gene. Analysis of differential expression circRNAs displayed that 136 circRNAs were differentially expressed at day 12 (Ad) after adipocyte differentiation, compared with the control at day 0 (Pread 0), while 7 circRNAs were detected on day 2. Sanger sequencing validated that six circRNAs had head-to-tail junction, and quantitative real-time PCR (qPCR) results revealed that the expression patterns of ten circRNAs were consistent with their expression levels from RNA-sequencing (RNA-seq) data. We further predicted the networks of circRNA-miRNA-gene based on miRNAs sponging by circRNAs, in which genes were participated in the adipocyte differentiation-related signaling pathways. After that, we constructed several adipocyte differentiation-related ceRNAs and revealed six circRNAs (novel_circ_0009127, novel_circ_0000628, novel_circ_0011513, novel_circ_0010775, novel_circ_0006981 and novel_circ_0001494) were related to adipogenesis. Furthermore, we analyzed the homology among yak, human and mouse circRNAs and found that 3536 yak circRNAs were homologous to human and mouse circRNAs. In conclusion, these findings provide a solid basis for the investigation of yak adipocyte differentiation-related circRNAs and serve as a great reference to study the energy metabolism of high-altitude animals.

Prevalence and molecular characterization of Cryptosporidium spp. in yaks (Bos grunniens) in Naqu, China

The intestinal protozoan specie, Cryptosporidium causes serious diarrheal syndrome in humans and animals worldwide. However, limited knowledge is known about the infection caused by this specie in yaks in Naqu. About 950 serum and 150 fecal samples were collected and assayed by using commercial ELISA kits and nPCR detection methods to find the prevalence and molecular characterization of Cryptosporidium spp. in yaks. Results found that 103 out of 950 (10.8%) serums were uncovered against C. parvum antibodies. In different regions, the prevalence of C. parvum in yaks were in a range from 9.1% to 16.7%, with obvious difference among the three areas (P < 0.001). In male and female yaks, the prevalence of C. parvum was found to be 7.2% and 13.3% respectively (P < 0.001); and a significant difference (P < 0.001) with a range of 9.8%–18.2% was observed among different age groups. Out of 150 fecal samples, only 2 (1.3%) positive samples were detected via nPCR. The positive samples were sequenced and identified to be C. bovis. The two isolates were clustered to cattle and yak clade separately. Our results highlight the prevalence and epidemiological status of Cryptosporidium spp. in yaks which may contribute towards the prevention and control of this zoonotic disease in Naqu, China.

Continuous chromosome-scale haplotypes assembled from a single interspecies F1 hybrid of yak and cattle.

BackgroundThe development of trio binning as an approach for assembling diploid genomes has enabled the creation of fully haplotype-resolved reference genomes. Unlike other methods of assembly for diploid genomes, this approach is enhanced, rather than hindered, by the heterozygosity of the individual sequenced. To maximize heterozygosity and simultaneously assemble reference genomes for 2 species, we applied trio binning to an interspecies F1 hybrid of yak (Bos grunniens) and cattle (Bos taurus), 2 species that diverged nearly 5 million years ago. The genomes of both of these species are composed of acrocentric autosomes.ResultsWe produced the most continuous haplotype-resolved assemblies for a diploid animal yet reported. Both the maternal (yak) and paternal (cattle) assemblies have the largest 2 chromosomes in single haplotigs, and more than one-third of the autosomes similarly lack gaps. The maximum length haplotig produced was 153 Mb without any scaffolding or gap-filling steps and represents the longest haplotig reported for any species. The assemblies are also more complete and accurate than those reported for most other vertebrates, with 97% of mammalian universal single-copy orthologs present.ConclusionsThe high heterozygosity inherent to interspecies crosses maximizes the effectiveness of the trio binning method. The interspecies trio binning approach we describe is likely to provide the highest-quality assemblies for any pair of species that can interbreed to produce hybrid offspring that develop to sufficient cell numbers for DNA extraction.

Cover Image, Volume 100, Issue 6

The cover image is based on the Research Article Yak (Bos grunniens) bones collagen‐derived peptides stimulate osteoblastic proliferation and differentiation via the activation of Wnt/β‐catenin signaling pathway by Mengliang Ye et al., https://doi.org/10.1002/jsfa.10286. image

Human Spotted Fever Group Rickettsia Infecting Yaks (Bos grunniens) in the Qinghai-Tibetan Plateau Area.

The Qinghai-Tibetan Plateau Area (QTPA) is a plateau with the highest average altitude, located in Northwestern China. There is a risk for interspecies disease transmission, such as spotted fever rickettsioses. However, information on the molecular characteristics of the spotted fever group (SFG) Rickettsia spp. in the area is limited. This study performed screenings, and detected the DNA of human pathogen, SFG Rickettsia spp., with 11.3% (25/222) infection rates in yaks (Bos grunniens). BLASTn analysis revealed that the Rickettsia sequences obtained shared 94.3–100% identity with isolates of Rickettsia spp. from ticks in China. One Rickettsia sequence (MN536161) had 100% nucleotide identity to two R. raoultii isolates from Chinese Homo sapiens, and one isolate from Qinghai Dermacentor silvarum. Meanwhile, another Rickettsia sequence (MN536157) shared 99.1–99.5% identity to one isolate from Dermacentor spp. in China. Furthermore, the phylogenetic analysis of SFG Rickettsia spp. ompA gene revealed that these two sequences obtained from yaks in the present study grouped with the R. slovaca and R. raoultii clades with isolates identified from Dermacentor spp. and Homo sapiens. Our findings showed the first evidence of human pathogen DNA, SFG Rickettsia spp., from animals, in the QTPA.

Cloning and Expression Analysis of Two Kdm Lysine Demethylases in the Testes of Mature Yaks and Their Sterile Hybrids.

Simple SummaryThe hybrid of male cattle (Bos taurus) with female yaks (Bos grunniens) is called the cattle–yak. All female cattle–yaks are fertile, but all males are sterile. To date, there is no clear conclusion on the mechanism leading to cattle–yak male sterility. The domain conservation and expression profiles of lysine histone demethylases (KDMs) suggest that they might play important roles during gametogenesis. The objective of this study was to explore the molecular mechanism for male sterility of yak hybrids based on two demethylases, KDM1A and KDM4B. The mRNA and protein expression of KDM1A and KDM4B were dramatically decreased in the testes of adult cattle–yaks compared with adult yaks. In addition, the level of H3K36me3 in the testes of cattle–yaks was significantly lower than in yaks. These results suggest that the male sterility of cattle–yaks might be associated with reduced histone methylation modifications. These results provide valuable epigenetic information regarding the molecular mechanism resulting in male sterility of cattle–yaks.The objective of this study was to explore the molecular mechanism for male sterility of yak hybrids based on two demethylases. Total RNA was extracted from the testes of adult yaks (n = 10) and yak hybrids (cattle–yaks, n = 10). The coding sequences (CDS) of two lysine demethylases (KDMs), KDM1A and KDM4B, were cloned by RT-PCR. The levels of KDM1A and KDM4B in yaks and cattle–yaks testes were detected using Real-time PCR and Western blotting for mRNA and protein, respectively. In addition, the histone methylation modifications of H3K36me3 and H3K27me3 were compared between testes of yaks and cattle–yaks using ELISA. The CDS of KDM1A and KDM4B were obtained from yak testes. The results showed that the CDS of KDM1A exhibited two variants: variant 1 has a CDS of 2622 bp, encoding 873 amino acids, while variant 2 has a CDS of 2562 bp, encoding 853 amino acids. The CDS of the KDM4B gene was 3351 bp in length, encoding 1116 amino acids. The mRNA and protein expression of KDM1A and KDM4B, as well as the level of H3K36me3, were dramatically decreased in the testes of cattle–yaks compared with yaks. The present results suggest that the male sterility of cattle–yaks might be associated with reduced histone methylation modifications.

Identification and verification of differentially expressed genes in yak mammary tissue during the lactation cycle.

Yaks (Bos grunniens) live primarily in the Qinghai-Tibetan plateau (altitude: 2000-5000 m). Their milk presents unusual characteristics, containing large amounts of solids including fat and protein, and it is, therefore, important to understand the genetic makeup of the yak. To identify potentially critical genes playing a role in yak mammary tissue from colostrum to mature milk phase of lactogenesis, the early lactation (colostrum) stage (ELS; day 1 after parturition) and mature lactation (milk) stage (MLS; day 15) were chosen for comparison. An ELS-specific cDNA library was established by suppression subtractive hybridization and 25 expressed sequence tags at ELS were identified by sequencing and alignment. To further confirm our results the expression levels of 21 genes during the lactation cycle were measured using quantitative real-time RT-PCR (qRT-PCR). The qRT-PCR results confirmed 9 significantly up-regulated genes at ELS vs. MLS in yak mammary tissue, in which the l-amino acid oxidase 1 (LAO1) and collagen, type I, alpha I (COL1A1) were the most significantly up-regulated. During the lactation cycle, the highest expression of some milk fat genes (i.e., XDH and FABP3) in yak mammary tissue appears earlier than that in dairy cow. Our data also indicate MYC potentially playing a central role through putative regulation of COL1A1, CD44, SPARC, FASN and GPAM.

Evolutionary Adaptation of Aquaporin-4 in Yak (Bos grunniens) Brain to High-Altitude Hypoxia of Qinghai-Tibetan Plateau.

Background: In high-altitude animals, brain cell resilience against hypoxia stress is one critical evolutionary step that has promoted individual survival and species adaptation to the environment. Aquaporin-4 (AQP4) is implicated in a number of physiopathological processes, particularly in the development of brain edema, and other functions such as the regulation of extracellular space volume, potassium buffering, waste clearance, and calcium signaling. Still, the role of AQP4 in the adaptation to high-altitude hypoxia remains unknown. The yak (Bos grunniens) is the only large mammal that is currently known to have adapted to the high-altitude hypoxic environment of the Qinghai-Tibet Plateau (>4000 m above sea level). Methods: In this study, we cloned the complementary DNA (cDNA) for yak AQP4 and analyzed structural differences of AQP4 between yak and cattle. We used reverse transcription quantitative polymerase chain reaction and western blot to investigate whether the expression of AQP4 mRNA and protein was different in brain of yak and cattle. In addition, immunohistochemistry was use to analyze the localization and expression of AQP4 in brain of yak and cattle. Results: Immunohistochemical results have shown that AQP4 is expressed in many regions of the yak brain, and both protein and messenger RNA (mRNA) levels are significantly lower than those of low-altitude cattle (Bos taurus). Phylogenetic analysis revealed that yak AQP4 is evolutionarily conserved. Interestingly, a substitution of Ala (cattle) to Ser in position 82, and eight additional amino acid residues composing an α-helix region are present in yak AQP4 protein. These sequence modifications potentially modulate the function of AQP4 in distinct environments. Conclusions: Our findings suggest that AQP4 may have an important role in the resistance to cerebral edema through low expression and maintenance of normal physiological function in the yak brain.

Promoter hypermethylation of PIWI/piRNA pathway genes associated with diminished pachytene piRNA production in bovine hybrid male sterility

ABSTRACT Hybrid male sterility (HMS) is a postzygotic reproductive isolation mechanism that enforces speciation. A bovine example of HMS is the yattle (also called dzo), an interspecies hybrid of taurine cattle (Bos taurus) and yak (Bos grunniens). The molecular mechanisms underlying HMS of yattle are not well understood. Epigenetic modifications of DNA methylation and P-element induced wimpy testis (PIWI)-interacting RNA (piRNAs) are important regulators in spermatogenesis. In this study, we investigated DNA methylation patterns and piRNA expression in adult testes in hybrid infertile yattle bulls and fertile cattle and yak bulls using whole genome bisulphite-seq and small RNA-seq. Promoter hypermethylation in yattle were associated with DNA methylation involved in gamete generation, piRNA metabolic processes, spermatogenesis, and spermatid development (P < 2.6 × 10−5). Male infertility in yattle was associated with the promoter hypermethylation-associated silencing of PIWI/piRNA pathway genes including PIWIL1, DDX4, PLD6, MAEL, FKBP6, TDRD1 and TDRD5. The downstream effects of silencing these genes were diminished production of 29- to 31- nucleotide pachytene piRNAs in yattle testes. Hypermethylation events at transposable element loci (LINEs, SINEs, and LTRs) were found in yattle. LINE-derived prepachytene piRNAs increased and SINE-derived prepachytene piRNAs were reduced in yattle testes. Our data suggests that DNA methylation affects the PIWI/piRNA pathway and is involved in gene expression and pachytene piRNA production during spermatogenesis in bovine HMS. DNA hypermethylation and disruption of piRNA production contributed to unsuccessful germ cell development that may drive bovine HMS.

Insight into unique somitogenesis of yak (Bos grunniens) with one additional thoracic vertebra

BackgroundThe yak is a species of livestock which is crucial for local communities of the Qinghai-Tibet Plateau and adjacent regions and naturally owns one more thoracic vertebra than cattle. Recently, a sub-population of yak termed as the Jinchuan yak has been identified with over half its members own a thoracolumbar vertebral formula of T15L5 instead of the natural T14L5 arrangement. The novel T15L5 positioning is a preferred genetic trait leading to enhanced meat and milk production. Selective breeding of this trait would have great agricultural value and exploration of the molecular mechanisms underlying this trait would both accelerate this process and provide us insight into the development and regulation of somitogenesis.ResultsHere we investigated the genetic background of the Jinchuan yak through resequencing fifteen individuals, comprising five T15L5 individuals and ten T14L5 individuals with an average sequencing depth of > 10X, whose thoracolumbar vertebral formulae were confirmed by anatomical observation. Principal component analysis, linkage disequilibrium analysis, phylogenetic analysis, and selective sweep analysis were carried out to explore Jinchuan yak’s genetic background. Three hundred and thirty candidate markers were identified as associated with the additional thoracic vertebrae and target sequencing was used to validate seven carefully selected markers in an additional 51 Jinchuan yaks. The accuracies of predicting 15 thoracic vertebrae and 20 thoracolumbar vertebrae with these 7 markers were 100.00 and 33.33% despite they both could only represent 20% of all possible genetic diversity. Two genes, PPP2R2B and TBLR1, were found to harbour the most candidate markers associated with the trait and likely contribute to the unique somitic number and identity according to their reported roles in the mechanism of somitogenesis.ConclusionsOur findings provide a clear depiction of the Jinchuan yak’s genetic background and a solid foundation for marker-assistant selection. Further exploitation of this unique population and trait could be promoted with the aid of our genomic resource.

Characteristics and Functions of the Rumen Microbial Community of Cattle-Yak at Different Ages.

A cattle-yak, which is a hybrid between a yak (Bos grunniens) and cattle (Bos taurus), is an important livestock animal, but basic questions regarding its physiology and environmental adaptation remain unanswered. To address this issue, the present study examined the species composition and functional characteristics of rumen microorganisms in the cattle-yak of different ages (2 and 3 years old) by metagenomic analysis. We found that rumen microbial community composition was similar at the two ages. Firmicutes, Fibrobacteres, Euryarchaeota, Bacteroidetes, and Proteobacteria were the predominant phyla, with Firmicutes accounting for the highest percentage of bacteria in 2-year-old (48%) and 3-year-old (46%) animals. Bacterial species involved in lignocellulose degradation were detected in the rumen of adult cattle-yaks including Ruminococcus flavefaciens, Ruminococcus albus, Fibrobacter succinogenes, and Prevotella ruminicola, with F. succinogenes being the most abundant. A total of 145,489 genes were annotated according to the Carbohydrate-active Enzyme database, which identified glycoside hydrolases as the most highly represented enzyme family. Further functional annotation revealed specific microflora and genes in the adult rumen that are potentially related to plateau adaptability. These results could explain the heterosis of the cattle-yak and provide insight into mechanisms of physiologic adaptation in plateau animals.