Copy number variation in intron 1 of SOX5 causes the Pea-comb phenotype in chickens

Cataloging copy number variation regions and allied diversity in goat breeds spanning pan India

Huge genetic diversity is evident among the diverse goat breeds in terms of production, reproduction, adaptability, growth, disease resistance and thermo-tolerance. This diversity is an outcome of both natural and artificial selection acting on the caprine genome over the years. A fine characterization of whole genome variation is now possible by employing Next Generation Sequencing (NGS) technologies. To explore underlying genetics, genome-wide analysis of genetic markers is the best resolution. The study strived to capture variation in terms of CNV/CNVRs among 11 Indian goat breeds. In this study, the first ever resequencing-based CNV/CNVR distribution of Indigenous goat breeds was delineated, providing a sizable addition to the prior caprine CNVRs reported. Different diversity metrics were analyzed using identified CNVR. Principal component analysis (PCA) showed separate clustering of Kanniadu (KAN) and Jharkhand Black (JB) from other breeds under the study, indicating their unique genetic profile as the former breeds were sampled from institutional farms. The admixture analysis and introgression revealed by f3 statistics suggested distinct genetic structuring of JB, KAN and TEL(Tellicherry) as compared to the rest of the studied populations. Apart from this, we also identified 32 selection signatures through VST (Variance-stabilizing transformation) method and key genes such as ZBTB7C, BHLHE22, AGT were found elucidating the genetic architecture of hot and cold adaptation in Indian goats. Information generated hereby in the form of 32,711 autosomal CNVRs and the custom scripts ( https://github.com/kkokay07/Climate-Variables-Analysis.git , https://github.com/chau-mau/SelectCNVR.git and https://github.com/chau-mau/CNVrecaller.git ) will be of relevance in further studies on copy number based genetics.

Skin regional specification and higher-order HoxC regulation

The integument plays a critical role in functional adaptation, with macro-regional specification forming structures like beaks, combs, feathers, and scales, while micro-regional specification modifies skin appendage shapes. However, the molecular mechanisms remain largely unknown. Craniofacial integument displays dramatic diversity, exemplified by the Polish chicken (PC) with a homeotic transformation of comb-to-crest feathers, caused by a 195-base pair (bp) duplication in HoxC10 intron. Micro-C analyses show that HoxC-containing topologically associating domain (TAD) is normally closed in the scalp but open in the dorsal and tail regions, allowing multiple long-distance contacts. In the PC scalp, the TAD is open, resulting in high HoxC expression. CRISPR-Cas9 deletion of the 195-bp duplication reduces crest feather formation, and HoxC misexpression alters feather shapes. The 195-bp sequence is found only in Archelosauria (crocodilians and birds) and not in mammals. These findings suggest that higher-order regulation of the HoxC cluster modulates gene expression, driving the evolution of adaptive integumentary appendages in birds.

Population genomic analysis identifies the complex structural variation at the fibromelanosis (FM) locus in chicken

Phenotypic diversity and its genetic basis are central questions in biology, with domesticated animals offering valuable insights due to their rapid evolution the last 10,000 years. In chickens, fibromelanosis (FM) is a striking pigmentation phenotype characterized by hyperpigmentation. A previous study identified a complex structural variant involving both two large duplications (127.4 and 170.5 kb in size) and inversions associated with upregulated expression of the Endothelin 3 (EDN3) gene. However, the detailed organization of the structural arrangements have remained unclear. In this study, we conducted a comprehensive genomic survey of 517 FM chickens representing 44 different populations. Our results elucidate the complex arrangement of the duplications and inversions at the FM locus based on the large-scale genomic survey, population level genotyping, and linkage disequilibrium analysis, providing conclusive support for one specific configuration of the two large duplications, resolving a controversy that has been unresolved for more than a decade. Our results show that the birth of this complex structural variant must have involved an interchromosomal rearrangement creating fixed heterozygosity due to sequence differences between the two copies of the 127.4 kb duplication. This study shows how population genomics can be used to understand complex structural variations that underlie phenotypic variation.

Genome wide detection of CNV and their association with body size in Danzhou chickens

Copy number variation (CNV) is a crucial component of genetic diversity in the genome, serving as the foundation for the genetic architecture and phenotypic variability of complex traits. In this study, we examined CNVs in the Danzhou (DZ) chicken, an indigenous breed exclusive to Hainan Province, China. By employing whole-genome resequencing data from 200 DZ chickens, we conducted a comprehensive genome-wide analysis of CNVs using CNVpytor and performed CNV-based genome-wide association studies (GWAS) on 6 body size traits, including body slope length (BSL), keel length (KeL), tibial length (TiL), tibial circumference (TiC), chest width (ChW), and chest depth (ChD) utilizing linear mixed model methods considering a genomic relationship matrix. We identified a total of 144,265 autosomal CNVs among the 200 individuals, comprising 67,818 deletions and 76,447 duplications. After merging these variants together, we obtained 4,824 distinct copy number variant regions, which accounted for approximately 20% of the chicken autosomal genome. Furthermore, we discovered several significantly associated CNV segments with body size traits located proximal to genes such as IHH, WNT6, WNT10A, LPR4, FZD2, WNT7B, and GNAS that have been extensively implicated in skeletal development and growth processes. These findings enhance our understanding of CNVs in chickens and their potential impact on body size traits by revealing candidate genes involved in the regulation of these traits. This establishes a solid framework for future studies and may prove particularly beneficial for exploring genetic structural variation in chickens.

Copy number variations within fibroblast growth factor 13 gene influence growth traits and alternative splicing in cattle

Previous researches revealed a copy number variation (CNV) region in the bovine fibroblast growth factor 13 (FGF13) gene. However, its effects remain unknown. This study detected the various copy number types in seven Chinese cattle breeds and analysed their population genetic characteristics and effects on growth traits and transcription levels. Copy number Loss was more frequent in Caoyuan Red cattle and Xianan cattle than in the other breeds. Association analysis between CNV and growth traits of Qinchuan indicated that the CNV was significantly related to chest depth, hip width and hucklebone width (P < 0.05). Additionally, the growth traits of individuals with copy number Loss were significantly inferior to those with copy number Gain or Median (P < 0.05). Besides, we found two splicing isoforms, AS1 and AS2, in FGF13 gene, which resulted from alternative 5' splicing sites of intron 1. These isoforms showed varied expression levels in various tissues. Moreover, CNV was significantly and negatively associated with the mRNA expression of AS1 (r = -0.525, P < 0.05). The CNVs in bovine FGF13 gene negatively regulated growth traits and gene transcription. These observations provide new insights into bovine FGF13 gene, delivering potentially useful information for future Chinese cattle breeding programs.

Genome-wide association study reveals 2 copy number variations associated with the variation of plumage color in the white duck hybrid population

Plumage color is an intuitive external poultry characteristic with rich manifestations and complex genetic mechanisms. In our previous study, we observed that there were more dark variations in plumage color in the F2 population derived from the hybridization of 2 white duck varieties. Therefore, based on the statistics of plumage color of 308 F2 populations, we further used the resequencing data of these individuals to detect copy number variations (CNVs) in the whole genome and conducted genome-wide association studies (GWAS) to determine the genetic basis related to plumage color traits. The CNV detection revealed 9,337 CNVs, with an average length of 15,950 bp and a total length of 142.02 MB, accounting for approximately 12.91% of the reference genome. The CNV distribution on the chromosomes was relatively uniform, and the number of CNVs on each chromosome positively correlated with the length of the chromosome. In the pure black plumage group, 2,101 CNVs were only identified, and 1,714 were specifically identified in the pure white plumage group. Ten CNVs were randomly selected for validation using quantitative real-time PCR, and 9 CNVs had the same CNV types as predicted, with an accuracy of 90%. Based on GWAS, we identified 2 CNVs potentially associated with plumage color variations, with the associated CNV regions covering 9 genes. Enrichment analysis of these 9 candidate genes showed significant enrichment of 3 pathways (ribosome biogenesis in eukaryotes, RNA transport, and protein export) and 17 gene ontology terms. Among these, VWA5A can downregulate MITF by binding to the regulatory factors SOX10. The occurrence of CNV may indirectly contribute to duck plumage color variation by affecting the regulatory factors of the switch gene MITF in the melanogenesis pathway. These findings have improved the understanding of the genetic basis of duck plumage color variation and have been beneficial for developing and using plumage color traits in subsequent poultry breeding.

De novo genome assembly of white clover (Trifolium repens L.) reveals the role of copy number variation in rapid environmental adaptation

BACKGROUND

White clover (Trifolium repens) is a globally important perennial forage legume. This species also serves as an eco-evolutionary model system for studying within-species chemical defense variation; it features a well-studied polymorphism for cyanogenesis (HCN release following tissue damage), with higher frequencies of cyanogenic plants favored in warmer locations worldwide. Using a newly generated haplotype-resolved genome and two other long-read assemblies, we tested the hypothesis that copy number variants (CNVs) at cyanogenesis genes play a role in the ability of white clover to rapidly adapt to local environments. We also examined questions on subgenome evolution in this recently evolved allotetraploid species and on chromosomal rearrangements in the broader IRLC legume clade.

RESULTS

Integration of PacBio HiFi, Omni-C, Illumina, and linkage map data yielded a completely de novo genome assembly for white clover (created without a priori sequence assignment to subgenomes). We find that white clover has undergone extensive transposon diversification since its origin but otherwise shows highly conserved genome organization and composition with its diploid progenitors. Unlike some other clover species, its chromosomal structure is conserved with other IRLC legumes. We further find extensive evidence of CNVs at the major cyanogenesis loci; these contribute to quantitative variation in the cyanogenic phenotype and to local adaptation across wild North American populations.

CONCLUSIONS

This work provides a case study documenting the role of CNVs in local adaptation in a plant species, and it highlights the value of pan-genome data for identifying contributions of structural variants to adaptation in nature.

Metabolomics reveals the reasons for the occurrence of Pendulous-comb related to egg production performance

The chicken comb is an essential secondary sexual characteristic to measure sexual maturity and is closely related to reproductive performance. Pendulous comb (PC) and upright comb (UC) are 2 common comb phenotypes in hens, which have been highly associated with egg production performance. However, the reasons for the formation of PC remain undetermined. In this study, we first characterized the PC and UC chicken at start (at 175 d age), peak (at 217 d age), and postlaying (at 300 d age) and found that PC and UC could transform for each other. Furthermore, we suggested that PC chicken demonstrated better egg production performance than UC chicken, especially characterizing comb type in the start-laying period. Moreover, we performed histological evaluation of PC and UC tissue, which suggested that the low density of collagen fibers and acid mucopolysaccharides might lead to the formation of PC. To further explore the possible reasons for PC formation, we performed an untargeted metabolomic analysis of serum between PC and UC chicken in the start, peak, and postlaying periods. The enrichment analysis of period-unique differentially expressed metabolites (DEMs) between PC and UC showed that the different metabolic pathways and nutritional levels might contribute to the formation of PC in the different laying periods. Our research provided critical insights into the phenotypic diversity of chicken comb, establishing a foundation for early selection of chicken egg production performance.

Copy number variant detection using next-generation sequencing in EYS-associated retinitis pigmentosa

Retinitis pigmentosa (RP) is the most common inherited retinal dystrophy and a major cause of blindness. RP is caused by several variants of multiple genes, and genetic diagnosis by identifying these variants is important for optimizing treatment and estimating patient prognosis. Next-generation sequencing (NGS), which is currently widely used for diagnosis, is considered useful but is known to have limitations in detecting copy number variations (CNVs). In this study, we re-evaluated CNVs in EYS, the main causative gene of RP, identified via NGS using multiplex ligation-dependent probe amplification (MLPA). CNVs were identified in NGS samples of eight patients. To identify potential CNVs, MLPA was also performed on samples from 42 patients who were undiagnosed by NGS but carried one of the five major pathogenic variants reported in Japanese EYS-RP cases. All suspected CNVs based on NGS data in the eight patients were confirmed via MLPA. CNVs were found in 2 of the 42 NGS-undiagnosed RP cases. Furthermore, results showed that 121 of the 661 patients with RP had EYS as the causative gene, and 8.3% (10/121 patients with EYS-RP) had CNVs. Although NGS using the CNV calling criteria utilized in this study failed to identify CNVs in two cases, no false-positive results were detected. Collectively, these findings suggest that NGS is useful for CNV detection during clinical diagnosis of RP.

The RHCE gene encodes the chicken blood system I

BACKGROUND

There are 13 known chicken blood systems, which were originally detected by agglutination of red blood cells by specific alloantisera. The genomic region or specific gene responsible has been identified for four of these systems (A, B, D and E). We determined the identity of the gene responsible for the chicken blood system I, using DNA from multiple birds with known chicken I blood system serology, 600K and 54K single nucleotide polymorphism (SNP) data, and lowpass sequence information.

RESULTS

The gene responsible for the chicken I blood system was identified as RHCE, which is also one of the genes responsible for the highly polymorphic human Rh blood group locus, for which maternal/fetal antigenic differences can result in fetal hemolytic anemia with fetal mortality. We identified 17 unique RHCE haplotypes in the chicken, with six haplotypes corresponding to known I system serological alleles. We also detected deletions in the RHCE gene that encompass more than 6000 bp and that are predicted to remove its last seven exons.

CONCLUSIONS

RHCE is the gene responsible for the chicken I blood system. This is the fifth chicken blood system for which the responsible gene and gene variants are known. With rapid DNA-based testing now available, the impact of I blood system variation on response against disease, general immune function, and animal production can be investigated in greater detail.

How structural variants shape avian phenotypes: Lessons from model systems

Despite receiving significant recent attention, the relevance of structural variation (SV) in driving phenotypic diversity remains understudied, although recent advances in long-read sequencing, bioinformatics and pangenomic approaches have enhanced SV detection. We review the role of SVs in shaping phenotypes in avian model systems, and identify some general patterns in SV type, length and their associated traits. We found that most of the avian SVs so far identified are short indels in chickens, which are frequently associated with changes in body weight and plumage colouration. Overall, we found that relatively short SVs are more frequently detected, likely due to a combination of their prevalence compared to large SVs, and a detection bias, stemming primarily from the widespread use of short-read sequencing and associated analytical methods. SVs most commonly involve non-coding regions, especially introns, and when patterns of inheritance were reported, SVs associated primarily with dominant discrete traits. We summarise several examples of phenotypic convergence across different species, mediated by different SVs in the same or different genes and different types of changes in the same gene that can lead to various phenotypes. Complex rearrangements and supergenes, which can simultaneously affect and link several genes, tend to have pleiotropic phenotypic effects. Additionally, SVs commonly co-occur with single-nucleotide polymorphisms, highlighting the need to consider all types of genetic changes to understand the basis of phenotypic traits. We end by summarising expectations for when long-read technologies become commonly implemented in non-model birds, likely leading to an increase in SV discovery and characterisation. The growing interest in this subject suggests an increase in our understanding of the phenotypic effects of SVs in upcoming years.

Copy number variant scan in more than four thousand Holstein cows bred in Lombardy, Italy

Copy Number Variants (CNV) are modifications affecting the genome sequence of DNA, for instance, they can be duplications or deletions of a considerable number of base pairs (i.e., greater than 1000 bp and up to millions of bp). Their impact on the variation of the phenotypic traits has been widely demonstrated. In addition, CNVs are a class of markers useful to identify the genetic biodiversity among populations related to adaptation to the environment. The aim of this study was to detect CNVs in more than four thousand Holstein cows, using information derived by a genotyping done with the GGP (GeneSeek Genomic Profiler) bovine 100K SNP chip. To detect CNV the SVS 8.9 software was used, then CNV regions (CNVRs) were detected. A total of 123,814 CNVs (4,150 non redundant) were called and aggregated into 1,397 CNVRs. The PCA results obtained using the CNVs information, showed that there is some variability among animals. For many genes annotated within the CNVRs, the role in immune response is well known, as well as their association with important and economic traits object of selection in Holstein, such as milk production and quality, udder conformation and body morphology. Comparison with reference revealed unique CNVRs of the Holstein breed, and others in common with Jersey and Brown. The information regarding CNVs represents a valuable resource to understand how this class of markers may improve the accuracy in prediction of genomic value, nowadays solely based on SNPs markers.

Landscape genomics reveals regions associated with adaptive phenotypic and genetic variation in Ethiopian indigenous chickens

Climate change is a threat to sustainable livestock production and livelihoods in the tropics. It has adverse impacts on feed and water availability, disease prevalence, production, environmental temperature, and biodiversity. Unravelling the drivers of local adaptation and understanding the underlying genetic variation in random mating indigenous livestock populations informs the design of genetic improvement programmes that aim to increase productivity and resilience. In the present study, we combined environmental, genomic, and phenotypic information of Ethiopian indigenous chickens to investigate their environmental adaptability. Through a hybrid sampling strategy, we captured wide biological and ecological variabilities across the country. Our environmental dataset comprised mean values of 34 climatic, vegetation and soil variables collected over a thirty-year period for 260 geolocations. Our biological dataset included whole genome sequences and quantitative measurements (on eight traits) from 513 individuals, representing 26 chicken populations spread along 4 elevational gradients (6-7 populations per gradient). We performed signatures of selection analyses ([Formula: see text] and XP-EHH) to detect footprints of natural selection, and redundancy analyses (RDA) to determine genotype-environment and genotype-phenotype-associations. RDA identified 1909 outlier SNPs linked with six environmental predictors, which have the highest contributions as ecological drivers of adaptive phenotypic variation. The same method detected 2430 outlier SNPs that are associated with five traits. A large overlap has been observed between signatures of selection identified by[Formula: see text]and XP-EHH showing that both methods target similar selective sweep regions. Average genetic differences measured by [Formula: see text] are low between gradients, but XP-EHH signals are the strongest between agroecologies. Genes in the calcium signalling pathway, those associated with the hypoxia-inducible factor (HIF) transcription factors, and sports performance (GALNTL6) are under selection in high-altitude populations. Our study underscores the relevance of landscape genomics as a powerful interdisciplinary approach to dissect adaptive phenotypic and genetic variation in random mating indigenous livestock populations.

The novel IMAGE001 genotyping array as a valuable alternative for genetic diversity screening in chicken: a demonstration in a local chicken breed in Belgium

Screening for genetic diversity in livestock species breeds is of utmost importance, especially for local, small populations that are at the risk of extinction. Luckily, recent developments in technology increase access to genotyping, also for numerically small breeds. One of these new technologies is the IMAGE001 single nucleotide polymorphism genotyping array that includes markers for 6 different species (cow, pig, sheep, chicken, horse and goat). For our current study, we studied the Turkey-headed Malines chicken, a local chicken breed in Belgium, for the first time. A total of 110 animals were genotyped, together with 29 samples from 4 supposedly related breeds. The genotypes were used to assess the genetic diversity of this local breed. Our analysis revealed an average inbreeding coefficient of 0.20 through runs of homozygosity analysis, and effective population size estimation based on linkage disequilibrium indicated a low genetic diversity (Ne = 34). Moreover, a principal component analysis and a genetic differentiation study (FST) were performed using these marker data to position the Turkey-headed Malines relative to the 4 other indigenous Belgian chicken breeds. Finally, we discussed the practical implications of the overlap between the IMAGE001 array and other existing chicken genotyping arrays. This study is the first use of the novel IMAGE001 array to evaluate a local chicken breed, and demonstrates it as a viable option for genomic characterization a breed. Moreover, with this research, we are able to provide a good basis for further evaluation of the Belgian chicken heritage.

Phylogenetic analysis reveals multiple origins of Chinese gamecocks

Cockfighting is popular worldwide, dating back to 2,800 BC. Primarily, 5 modern Chinese gamecock breeds exist, located in the northeast (Luxi and Henan), west (Turpan), south (Xishuangbanna), and southeast (Zhangzhou) of China. However, whether Chinese gamecocks were derived from a single origin or multiple origins remains controversial. Therefore, this study used next-generation resequencing data to elucidate the origin of Chinese gamecocks by constructing genome-wide and SRY-box transcription factor 5 (SOX5) gene phylogenetic trees. Data from 161 chickens from 27 breeds, including 9 gamecock breeds, were included. Before constructing the SOX5 gene tree, we validated that the pea-comb phenotype mutation in all gamecock breeds was attributed to copy number variation in intron 1 of the SOX5 gene, as previously reported. The specific region was chr1: 65,838,000 to 65,846,000. The phylogenetic tree results suggested that Zhangzhou and Xishuangbanna gamecocks have a monophyletic origin, while Luxi, Henan, and Turpan gamecocks have a common ancestor. Our study provides genome-wide evidence that Chinese gamecocks have multiple origins and advances the understanding of the genetic mechanisms of the pea-comb characteristic.

Finding Predictors of Leg Defects in Pigs Using CNV-GWAS

One of the most important areas of modern genome research is the search for meaningful relationships between genetic variants and phenotypes. In the livestock field, there has been research demonstrating the influence of copy number variants (CNVs) on phenotypic variation. Despite the wide range in the number and size of detected CNVs, a significant proportion differ between breeds and their functional effects are underestimated in the pig industry. In this work, we focused on the problem of leg defects in pigs (lumps/growths in the area of the hock joint on the hind legs) and focused on searching for molecular genetic predictors associated with this trait for the selection of breeding stock. The study was conducted on Large White pigs using three CNV calling tools (PennCNV, QuantiSNP and R-GADA) and the CNVRanger association analysis tool (CNV-GWAS). As a result, the analysis identified three candidate CNVRs associated with the formation of limb defects. Subsequent functional analysis suggested that all identified CNVs may act as potential predictors of the hock joint phenotype of pigs. It should be noted that the results obtained indicate that all significant regions are localized in genes (CTH, SRSF11, MAN1A1 and LPIN1) responsible for the metabolism of amino acids, fatty acids, glycerolipids and glycerophospholipids, thereby related to the immune response, liver functions, content intramuscular fat and animal fatness. These results are consistent with previously published studies, according to which a predisposition to the formation of leg defects can be realized through genetic variants associated with the functions of the liver, kidneys and hematological characteristics.

HOXB8 overexpression induces morphological changes in chicken mandibular skin: an RNA-seq analysis

The Huiyang beard chicken is a well-known Chinese local breed known for its elongated feathers gathered from both sides of the face (muffs) and below the beak (beard), as well as short wattles (SW). The muff and beard (Mb) mutation is caused by ectopic upregulation of the homeobox B8 (HOXB8) gene in the mandibular skin; and the chi-square test showed a significant correlation between SW and Mb genotypes. However, the underlying molecular mechanisms that regulate Mb and SW variations remain unclear. In this study, we investigated the transcriptomes of the mandibular skin and wattles of chickens with and without the Mb genotype to elucidate the molecular basis of these traits. Our results show that HOXB8 is expressed at significantly higher levels in both the mandibular skin and wattles of Mb chickens than in those of wild-type chickens, indicating that HOXB8 regulates both the Mb and SW phenotypes. Key genes for keratin synthesis were highly expressed in the mandibular skin of Mb chickens, suggesting that HOXB8 may play a role in feather development. In wattles, changes in the expression of extracellular matrix synthesis genes may contribute to SW traits. DNA-binding motif analyses revealed that differentially expressed genes were likely to be directly regulated by HOXB8 binding, indicating that HOXB8 may directly or indirectly regulate feather follicle development and wattle growth. Our study identified both known and novel targets, including several genes not previously implicated in feather development and mesenchymal formation. These findings provide insights into the molecular mechanisms of skin appendage variation in birds and offer potential applications in breeding poultry breeds with unique phenotypes.

Identification of copy number variation in Tibetan sheep using whole genome resequencing reveals evidence of genomic selection

BACKGROUND

Copy number variation (CNV) is an important source of structural variation in the mammalian genome. CNV assays present a new method to explore the genomic diversity of environmental adaptations in animals and plants and genes associated with complex traits. In this study, the genome-wide CNV distribution characteristics of 20 Tibetan sheep from two breeds (10 Oula sheep and 10 Panou sheep) were analysed using whole-genome resequencing to investigate the variation in the genomic structure of Tibetan sheep during breeding.

RESULTS

CNVs were detected using CNVnator, and the overlapping regions of CNVs between individual sheep were combined. Among them, a total of 60,429 CNV events were detected between the indigenous sheep breed (Oula) and the synthetic sheep breed (Panou). After merging the overlapping CNVs, 4927 CNV regions (CNVRs) were finally obtained. Of these, 4559 CNVRs were shared by two breeds, and there were 368 differential CNVRs. Deletion events have a higher percentage of occurrences than duplication events. Functional enrichment analysis showed that the shared CNVRs were significantly enriched in 163 GO terms and 62 KEGG pathways, which were mainly associated with organ development, neural regulation, immune regulation, digestion and metabolism. In addition, 140 QTLs overlapped with some of the CNVRs at more than 1 kb, such as average daily gain QTL, body weight QTL, and total lambs born QTL. Many of the CNV-overlapping genes such as PPP3CA, SSTR1 and FASN, overlap with the average daily weight gain and carcass weight QTL regions. Moreover, VST analysis showed that XIRP2, ABCB1, CA1, ASPA and EEF2 differed significantly between the synthetic breed and local sheep breed. The duplication of the ABCB1 gene may be closely related to adaptation to the plateau environment in Panou sheep, which deserves further study. Additionally, cluster analysis, based on all individuals, showed that the CNV clustering could be divided into two origins, indicating that some Tibetan sheep CNVs are likely to arise independently in different populations and contribute to population differences.

CONCLUSIONS

Collectively, we demonstrated the genome-wide distribution characteristics of CNVs in Panou sheep by whole genome resequencing. The results provides a valuable genetic variation resource and help to understand the genetic characteristics of Tibetan sheep. This study also provides useful information for the improvement and breeding of Tibetan sheep in the future.

Detection distribution of CNVs of SNX29 in three goat breeds and their associations with growth traits

As a member of the SNX family, the goat sorting nexin 29 (SNX29) is initially identified as a myogenesis gene. Therefore, this study aimed to examine the polymorphism in the SNX29 gene and its association with growth traits. In this study, we used an online platform to predict the structures of the SNX29 protein and used quantitative real-time PCR to detect potential copy number variation (CNV) in Shaanbei white cashmere (SBWC) goats (n = 541), Guizhou black (GB) goats (n = 48), and Nubian (NB) goats (n = 39). The results showed that goat SNX29 protein belonged to non-secretory protein. Then, five CNVs were detected, and their association with growth traits was analyzed. In SBWC goats, CNV1, CNV3, CNV4, and CNV5 were associated with chest width and body length (P < 0.05). Among them, the CNV1 individuals with gain and loss genotypes were superior to those individuals with a median genotype, but CNV4 and CNV5 of individuals with the median genotype were superior to those with the loss and gain genotypes. In addition, individuals with the gain genotype had superior growth traits in CNV3. In brief, this study suggests that the CNV of SNX29 can be used as a molecular marker in goat breeding.

Whole Genome Resequencing Helps Study Important Traits in Chickens

The emergence of high-throughput sequencing technology promotes life science development, provides technical support to analyze many life mechanisms, and presents new solutions to previously unsolved problems in genomic research. Resequencing technology has been widely used for genome selection and research on chicken population structure, genetic diversity, evolutionary mechanisms, and important economic traits caused by genome sequence differences since the release of chicken genome sequence information. This article elaborates on the factors influencing whole genome resequencing and the differences between these factors and whole genome sequencing. It reviews the important research progress in chicken qualitative traits (e.g., frizzle feather and comb), quantitative traits (e.g., meat quality and growth traits), adaptability, and disease resistance, and provides a theoretical basis to study whole genome resequencing in chickens.

Systematic Selection Signature Analysis of Chinese Gamecocks Based on Genomic and Transcriptomic Data

Selection pressures driven by natural causes or human interference are key factors causing genome variants and signatures of selection in specific regions of the genome. Gamecocks were bred for cockfighting, presenting pea-combs, larger body sizes, stronger limbs, and higher levels of aggression than other chickens. In this study, we aimed to explore the genomic differences between Chinese gamecocks and commercial, indigenous, foreign, and cultivated breeds by detecting the regions or sites under natural or artificial selection using genome-wide association studies (GWAS), genome-wide selective sweeps based on the genetic differentiation index (F_ST), and transcriptome analyses. Ten genes were identified using GWAS and F_ST: gga-mir-6608-1, SOX5, DGKB, ISPD, IGF2BP1, AGMO, MEOX2, GIP, DLG5, and KCNMA1. The ten candidate genes were mainly associated with muscle and skeletal development, glucose metabolism, and the pea-comb phenotype. Enrichment analysis results showed that the differentially expressed genes between the Luxi (LX) gamecock and Rhode Island Red (RIR) chicken were mainly related to muscle development and neuroactive-related pathways. This study will help to understand the genetic basis and evolution of Chinese gamecocks and support the further use of gamecocks as an excellent breeding material from a genetic perspective.

Variations in BCO2 Coding Sequence Causing a Difference in Carotenoid Concentration in the Skin of Chinese Indigenous Chicken

Carotenoid consumption decreases the risk of cancer, osteoporosis, or neurodegenerative diseases through interrupting the formation of free radicals. The deposition of carotenoids in chicken skin makes the skin color turn from white into yellow. The enzyme β-carotene oxygenase 2 (BCO2) plays a key role during the degradation process of carotenoids in skin. How the BCO2 affects the skin color of the chicken and whether it is the key factor that results in the phenotypic difference between yellow- and white-skin chickens are still unclear. In this research, the measurement of the concentration of carotenoids in chicken skin by HPLC showed that the carotenoid concentration in chickens with a yellow skin was significantly higher than that in white-skin chickens. Moreover, there were significant differences in BCO2 gene expression in the back skin between yellow- and white-skin chickens. Scanning the SNPs in BCO2 gene revealed a G/A mutation in exon 6 of the BCO2 gene in white and yellow skin chicken. Generally, one SNP c.890A>G was found to be associated with the chicken skin color and may be used as a genetic marker in breeding for yellow skin in Chinese indigenous chickens.

Selective footprints and genes relevant to cold adaptation and other phenotypic traits are unscrambled in the genomes of divergently selected chicken breeds

BACKGROUND

The genomes of worldwide poultry breeds divergently selected for performance and other phenotypic traits may also be affected by, and formed due to, past and current admixture events. Adaptation to diverse environments, including acclimation to harsh climatic conditions, has also left selection footprints in breed genomes.

RESULTS

Using the Chicken 50K_CobbCons SNP chip, we genotyped four divergently selected breeds: two aboriginal, cold tolerant Ushanka and Orloff Mille Fleur, one egg-type Russian White subjected to artificial selection for cold tolerance, and one meat-type White Cornish. Signals of selective sweeps were determined in the studied breeds using three methods: (1) assessment of runs of homozygosity islands, (2) F_ST based population differential analysis, and (3) haplotype differentiation analysis. Genomic regions of true selection signatures were identified by two or more methods or in two or more breeds. In these regions, we detected 540 prioritized candidate genes supplemented them with those that occurred in one breed using one statistic and were suggested in other studies. Amongst them, SOX5, ME3, ZNF536, WWP1, RIPK2, OSGIN2, DECR1, TPO, PPARGC1A, BDNF, MSTN, and beta-keratin genes can be especially mentioned as candidates for cold adaptation. Epigenetic factors may be involved in regulating some of these important genes (e.g., TPO and BDNF).

CONCLUSION

Based on a genome-wide scan, our findings can help dissect the genetic architecture underlying various phenotypic traits in chicken breeds. These include genes representing the sine qua non for adaptation to harsh environments. Cold tolerance in acclimated chicken breeds may be developed following one of few specific gene expression mechanisms or more than one overlapping response known in cold-exposed individuals, and this warrants further investigation.

Genome-Wide Genetic Structure of Henan Indigenous Chicken Breeds

There are five indigenous chicken breeds in Henan Province, China. These breeds have their own unique phenotypic characteristics in terms of morphology, behavior, skin and feather color, and productive performance, but their genetic basis is not well understood. Therefore, we analyzed the genetic structure, genomic diversity, and migration history of Henan indigenous chicken populations and the selection signals and genes responsible for Henan gamecock unique phenotypes using whole genome resequencing. The results indicate that Henan native chickens clustered most closely with the chicken populations in neighboring provinces. Compared to other breeds, Henan gamecock's inbreeding and selection intensity were more stringent. TreeMix analysis revealed the gene flow from southern chicken breeds into the Zhengyang sanhuang chicken and from the Xichuan black-bone chicken into the Gushi chicken. Selective sweep analysis identified several genes and biological processes/pathways that were related to body size, head control, muscle development, reproduction, and aggression control. Additionally, we confirmed the association between genotypes of SNPs in the strong selective gene LCORL and body size and muscle development in the Gushi-Anka F2 resource population. These findings made it easier to understand the traits of the germplasm and the potential for using the Henan indigenous chicken.

Integration of transcriptome sequencing and whole genome resequencing reveal candidate genes in egg production of upright and pendulous-comb chickens

Egg production performance plays an important role in the poultry industry across the world. Previous studies have shown a great difference in egg production performance between pendulous-comb (PC) and upright-comb (UC) chickens. However, there are no reports to identify potential candidate genes for egg production in PC and UC chickens. In the present study, 1,606 laying chickens were raised, and the egg laid by individual chicken was collected for 100 d. Moreover, the expression level of estrogen and progesterone hormones was measured at the start-laying and peak-laying periods of hens. Besides, 4 PC and 4 UC chickens were selected at 217 d of age to perform transcriptome sequencing (RNA-seq) and whole genome resequencing (WGS) to screen the potential candidate genes of egg production. The results showed that PC chicken demonstrated better egg production performance (P < 0.05) and higher estrogen and progesterone hormone expression levels than UC chicken (P < 0.05). RNA-seq analysis showed that 341 upregulated and 1,036 downregulated differentially expressed genes (DEGs) were identified in the ovary tissues of PC and UC chickens. These DEGs were mainly enriched in protein-related, lipid-related, and nucleic acids-related biological processes including ribosome, peptide biosynthetic process, lipid transport terms, and catalytic activity acting on RNA which can significantly affect egg production in chicken. The enrichment results of WGS analysis were consistent with RNA-seq. Further, joint analysis of WGS and RNA-seq data was utilized to screen 30 genes and CAMK1D, CLSTN2, MAST2, PIK3C2G, TBC1D1, STK3, ADGRB3, and PPARGC1A were identified as potential candidate genes for egg production in PC and UC chickens. In summary, our study provides a wealth of information for a better understanding of the genetic and molecular mechanism for the future breeding of PC and UC chickens for egg production.

Comprehensive Analysis of Copy Number Variations on Glycoside Hydrolase 45 Genes among Different Bursaphelenchus xylophilus Strains

Bursaphelenchus xylophilus is considered the most dangerous quarantine pest in China. It causes enormous economic and ecological losses in many countries from Asia and Europe. The glycoside hydrolase 45 gene family has been demonstrated in early studies to contribute to the cell wall degradation ability of B. xylophilus during its infection. However, the copy number variation (CNV) of the GH45 gene and its association with B. xylophilus pathogenicity were not fully elucidated. In this study, we found that the GH45 gene with two copies is the most predominant type among 259 B. xylophilus strains collected from China and Japan. Additionally, 18 strains are identified as GH45 genes with a single copy, and only two strains are verified to have three copies. Subsequent expression analysis and inoculation test suggest that the copy numbers of the GH45 gene are correlated with gene expression as well as the B. xylophilus pathogenicity. B. xylophilus strains with more copies of the GH45 gene usually exhibit more abundant expression and cause more severe wilt symptoms on pine trees. The aforementioned results indicated the potential regulatory effects of CNV in B. xylophilus and provided novel information to better understand the molecular pathogenesis of this devastating pest.

Copy Number Variation of the SOX6 Gene and Its Associations with Growth Traits in Ashidan Yak

Copy number variation (CNV) is a fundamental type of structural variation of the genome affecting the economic traits of livestock. The SOX6 gene (sex-determining region Y-box 6), as a transcription factor, has multiple functions with regard to sex determination, embryonic growth, the nervous system development, as well as bone, and various organ formation. This study employed quantitative real-time fluorescence quota PCR (qPCR) for detecting the SOX6-CNV of the 311 Ashidan yaks and analyzed the correlation of the SOX6-CNV with four phenotypes (including body weight, withers height, body length, and chest girth) of the yaks aged 6, 12, 18, and 30 months using ANOVA and multiple comparisons. Furthermore, the SOX6 gene expression was identified in seven different tissues of the yaks. The experiment results demonstrated the expression of SOX6 in each tissue, and the kidney and muscle tissue were found to have higher relative expression levels. Based on the processing by IBM SPSS software, SOX6-CNV was significantly correlated with the chest girth of the 6-months old yaks (p < 0.05) and 30-months yaks (p < 0.05), and withers height of 6 months yaks (p < 0.05) and 18-months yaks (p < 0.05), as well as the normal type of CNV, was chosen for yak breeding. In conclusion, SOX6 might be prominently involved in promoting growth and development of yaks, suggesting that the SOX6 gene can be used in breeding yaks by molecular marker-assisted selection (MAS). The study also offered some important insights into the references and clues for the genetic breeding of yaks.

A ∼ 4.1 kb deletion in IRX1 gene upstream is completely associated with rumplessness in Piao chicken

Piao chicken, a Chinese indigenous rumpless chicken breed, lacks pygostyle, caudal vertebra, uropygial gland and tail feathers. The rumplessness in Piao chicken presents an autosomal dominant inheritance pattern. However, the molecular genetic mechanisms underlying the rumplessness in Piao chicken remains unclear. In this study, whole-genome resequencing was performed for 146 individuals from 10 chicken breeds, including 9 tailed chicken breeds and Piao rumpless breed. Tailbone CT scan for Piao chickens and WL chickens, revealed that some Piao chicken tails were normal in number, and for a few Piao chickens tail length and tail bone numbers were between the rumpless and the normal tailed chickens. The results showed that the rumpless phenotype has not been completely fixed in Piao chicken breed. Using selection signature analysis and structural variation detection, we found a 4174 bp deletion located in the upstream region of IRX1 gene on chromosome 2 related to rumpless phenotype. Structural variation genotyping showed that the deletion was present in all 32 rumpless Piao chickens (del/del, wild/del) and absent from all 112 tailed chickens included in the dataset for the other 9 breeds and 2 tailed Piao chickens (wild/wild). In summary, all rumpless Piao chickens tested here carry this deletion mutation, to show a complete linkage association with rumplessness trait. We suggested that the 4174 bp deletion could be causative for rumpless phenotype in Piao chicken since this is the only mutation to show the complete linkage disequilibrium with rumplessness on whole genome level across all of 146 chickens from the 10 breeds. This study could facilitate a better understanding of the genetic characteristics of Piao chicken.

Comprehensive analysis of structural variants in chickens using PacBio sequencing

Structural variants (SVs) are one of the main sources of genetic variants and have a greater impact on phenotype evolution, disease susceptibility, and environmental adaptations than single nucleotide polymorphisms (SNPs). However, SVs remain challenging to accurately type, with several detection methods showing different limitations. Here, we explored SVs from 10 different chickens using PacBio technology and detected 49,501 high-confidence SVs. The results showed that the PacBio long-read detected more SVs than Illumina short-read technology genomes owing to some SV sites on chromosomes, which are related to chicken growth and development. During chicken domestication, some SVs beneficial to the breed or without any effect on the genomic function of the breed were retained, whereas deleterious SVs were generally eliminated. This study could facilitate the analysis of the genetic characteristics of different chickens and provide a better understanding of their phenotypic characteristics at the SV level, based on the long-read sequencing method. This study enriches our knowledge of SVs in chickens and improves our understanding of chicken genomic diversity.

Genomic and gene expression associations to morphology of a sexual ornament in the chicken

How sexual selection affects the genome ultimately relies on the strength and type of selection, and the genetic architecture of the involved traits. While associating genotype with phenotype often utilizes standard trait morphology, trait representations in morphospace using geometric morphometric approaches receive less focus in this regard. Here, we identify genetic associations to a sexual ornament, the comb, in the chicken system (Gallus gallus). Our approach combined genome-wide genotype and gene expression data (>30k genes) with different aspects of comb morphology in an advanced intercross line (F8) generated by crossing a wild-type Red Junglefowl with a domestic breed of chicken (White Leghorn). In total, 10 quantitative trait loci were found associated to various aspects of comb shape and size, while 1,184 expression QTL were found associated to gene expression patterns, among which 98 had overlapping confidence intervals with those of quantitative trait loci. Our results highlight both known genomic regions confirming previous records of a large effect quantitative trait loci associated to comb size, and novel quantitative trait loci associated to comb shape. Genes were considered candidates affecting comb morphology if they were found within both confidence intervals of the underlying quantitative trait loci and eQTL. Overlaps between quantitative trait loci and genome-wide selective sweeps identified in a previous study revealed that only loci associated to comb size may be experiencing on-going selection under domestication.

Molecular genetic variation of animals and plants under domestication

Domesticated plants and animals played crucial roles as models for evolutionary change by means of natural selection and for establishing the rules of inheritance, originally proposed by Charles Darwin and Gregor Mendel, respectively. Here, we review progress that has been made during the last 35 y in unraveling the molecular genetic variation underlying the stunning phenotypic diversity in crops and domesticated animals that inspired Mendel and Darwin. We notice that numerous domestication genes, crucial for the domestication process, have been identified in plants, whereas animal domestication appears to have a polygenic background with no obvious "domestication genes" involved. Although model organisms, such as Drosophila and Arabidopsis, have replaced domesticated species as models for basic research, the latter are still outstanding models for evolutionary research because phenotypic change in these species represents an evolutionary process over thousands of years. A consequence of this is that some alleles contributing to phenotypic diversity have evolved by accumulating multiple changes in the same gene. The continued molecular characterization of crops and farm animals with ever sharper tools is essential for future food security.

Population Genomic Sequencing Delineates Global Landscape of Copy Number Variations that Drive Domestication and Breed Formation of in Chicken

Copy number variation (CNV) is an important genetic mechanism that drives evolution and generates new phenotypic variations. To explore the impact of CNV on chicken domestication and breed shaping, the whole-genome CNVs were detected via multiple methods. Using the whole-genome sequencing data from 51 individuals, corresponding to six domestic breeds and wild red jungle fowl (RJF), we determined 19,329 duplications and 98,736 deletions, which covered 11,123 copy number variation regions (CNVRs) and 2,636 protein-coding genes. The principal component analysis (PCA) showed that these individuals could be divided into four populations according to their domestication and selection purpose. Seventy-two highly duplicated CNVRs were detected across all individuals, revealing pivotal roles of nervous system (NRG3, NCAM2), sensory (OR), and follicle development (VTG2) in chicken genome. When contrasting the CNVs of domestic breeds to those of RJFs, 235 CNVRs harboring 255 protein-coding genes, which were predominantly involved in pathways of nervous, immunity, and reproductive system development, were discovered. In breed-specific CNVRs, some valuable genes were identified, including HOXB7 for beard trait in Beijing You chicken; EDN3, SLMO2, TUBB1, and GFPT1 for melanin deposition in Silkie chicken; and SORCS2 for aggressiveness in Luxi Game fowl. Moreover, CSMD1 and NTRK3 with high duplications found exclusively in White Leghorn chicken, and POLR3H, MCM9, DOCK3, and AKR1B1L found in Recessive White Rock chicken may contribute to high egg production and fast-growing traits, respectively. The candidate genes of breed characteristics are valuable resources for further studies on phenotypic variation and the artificial breeding of chickens.

Copy number variation of the CCDC39 gene is associated with growth traits in Chinese cattle

Background

Copy number variation (CNV) has become an essential part of genetic structural variation. Coiled‐coil domain containing 39 (CCDC39) is a gene that related to the growth and development of organs and tissues. It is identified that it has a CNV region by animal genome resequencing.

Objective

In this study, we detected the phenotypic traits and different distributions of CCDC39 gene copy numbers in five Chinese cattle breeds (Qinchuan (QC) cattle, Yunling (YL) cattle, Xianan (XN) cattle, Pinan (PN) cattle and Jiaxian (JX) cattle).

Methods

Five hundred and six cattle were randomly selected for CNV distribution detection. Blood samples were taken and genomic DNA was extracted. Different tissues were obtained from adult (n = 3) XN cattle, including heart, liver, kidney, skeletal muscle and lung. The genome qPCR experiment was performed with SYBR Green in triplicate. CDNA qPCR was used to detect the expression level of CCDC39 in different tissues and varieties. Using SPSS v20.0 software, the relationship between CCDC39 CNV and the growth traits of PN, XN, QC, NY and YL cattle breeds was analyzed by one‐way analysis of variance (ANOVA).

Results

The results showed that the expression of CCDC39 in lung was higher than that in other tissues. The expression in liver and kidney was similar, but the expression in heart and muscle was less. It can be seen that the duplication type of QC cattle CCDC39 CNV is higher than the deletion or normal in the height at hip cross. The normal type of PN cattle in body length and hip width was better than duplication and deletion (p < 0.05). In XN cattle, the deletion type of CNV had superior growth characteristics in heart girth and cannon bone circumference compared with the duplication type and the normal type (p < 0.05).

Conclusion

The study revealed a significant association between CNV of CCDC39 gene and growth traits in different Chinese cattle breeds.

CNV analysis of VAMP7 gene reveals variation associated with growth traits in Chinese cattle

Copy number variant (CNV), a common genetic polymorphism, is closely related to the phenotypic variation traits of organisms. Vesicle-associated membrane protein 7 gene (VAMP7) codes a protein, which is a member of the SNARE proteins family and plays an important role in the process of intracellular vesicle transport. In this study, a total of four cattle breeds (Yunling cattle, Xianan cattle, Pinan cattle, Jiaxian red cattle) were used to investigate the copy numbers, and we found an association relationship between CNV of VAMP7 gene and growth traits of cattle by SPSS 20.0 software. The results showed that the CNV type of VAMP7 gene in four cattle breeds had the same distribution, Duplication type occupies a dominant position among the four varieties. In Yunling cattle, the Duplication type of VAMP7 is significantly related to the height at the hip cross (p < 0.05), Individuals with Duplication type commonly have less performance on growth and development, which indicates that the Duplication type of the VAMP7 gene may have a negative effect on cattle growth. Individuals with the other two CNV types may become the breeding direction of the VAMP7 gene. This study provided a new perspective and basic material for the molecular genetics of the CNV of the VAMP7 gene, and also promoted the breeding progress of Chinese local cattle.

Bacteriophage self-counting in the presence of viral replication

When host cells are in low abundance, temperate bacteriophages opt for dormant (lysogenic) infection. Phage lambda implements this strategy by increasing the frequency of lysogeny at higher multiplicity of infection (MOI). However, it remains unclear how the phage reliably counts infecting viral genomes even as their intracellular number increases because of replication. By combining theoretical modeling with single-cell measurements of viral copy number and gene expression, we find that instead of hindering lambda's decision, replication facilitates it. In a nonreplicating mutant, viral gene expression simply scales with MOI rather than diverging into lytic (virulent) and lysogenic trajectories. A similar pattern is followed during early infection by wild-type phage. However, later in the infection, the modulation of viral replication by the decision genes amplifies the initially modest gene expression differences into divergent trajectories. Replication thus ensures the optimal decision-lysis upon single-phage infection and lysogeny at higher MOI.

Identification of polymorphic loci in the deiodinase 2 gene and their associations with head dimensions in geese

Objective

This study was conducted to clone and compare the molecular characteristics of the deiodinase 2 (DIO2) gene between Sichuan White geese and Landes geese, and to analyze the association between polymorphisms of the DIO2 gene and head dimensions in Tianfu meat geese.

Methods

The coding sequence of the DIO2 gene was cloned by polymerase chain reaction (PCR) and vector ligation and aligned by DNAMAN software. A total of 350 Tianfu meat geese were used to genotype the polymorphisms of the DIO2 gene and measure the head dimensions. Association analysis between the polymorphisms of the DIO2 gene and head dimensions was carried out.

Results

An 840-bp coding sequence of the DIO2 gene was obtained and comparison analysis identified four polymorphic loci between Sichuan White geese and Landes geese. Further analysis showed that the dominant alleles for the four polymorphic loci were G, G, A, and T and the frequency of the heterozygous genotype was higher than that of the homozygous genotype in Tianfu meat geese. Compared to that in the population of non-knob geese of Tianfu meat geese, the head dimensions in the population of knob geese were significantly higher except for nostril height. However, in the non-knob geese, beak width 1 (BW1), beak width 2 (BW2), nostril length (NL), cranial width 1 (CW1), and maxillary length (ML) had significant differences among different genotypes or haplotypes/diplotypes.

Conclusion

These results suggested that polymorphisms of the DIO2 gene could be considered molecular markers to select larger heads of geese in the population of non-knob geese.

Cis-acting mutation affecting GJA5 transcription is underlying the Melanotic within-feather pigmentation pattern in chickens

Melanotic (Ml) is a mutation in chickens that extends black (eumelanin) pigmentation in normally brown or red (pheomelanin) areas, thus affecting multiple within-feather patterns [J. W. Moore, J. R. Smyth Jr, J. Hered. 62, 215-219 (1971)]. In the present study, linkage mapping using a back-cross between Dark Cornish (Ml/Ml) and Partridge Plymouth Rock (ml+/ml+ ) chickens assigned Ml to an 820-kb region on chromosome 1. Identity-by-descent mapping, via whole-genome sequencing and diagnostic tests using a diverse set of chickens, refined the localization to the genomic region harboring GJA5 encoding gap-junction protein 5 (alias connexin 40) previously associated with pigmentation patterns in zebrafish. An insertion/deletion polymorphism located in the vicinity of the GJA5 promoter region was identified as the candidate causal mutation. Four different GJA5 transcripts were found to be expressed in feather follicles and at least two showed differential expression between genotypes. The results showed that Melanotic constitutes a cis-acting regulatory mutation affecting GJA5 expression. A recent study established the melanocortin-1 receptor (MC1R) locus and the interaction between the MC1R receptor and its antagonist agouti-signaling protein as the primary mechanism underlying variation in within-feather pigmentation patterns in chickens. The present study advances understanding the mechanisms underlying variation in plumage color in birds because it demonstrates that the activity of connexin 40/GJA5 can modulate the periodic pigmentation patterns within individual feathers.

Brain Transcriptomics of Wild and Domestic Rabbits Suggests That Changes in Dopamine Signaling and Ciliary Function Contributed to Evolution of Tameness

Domestication has resulted in immense phenotypic changes in animals despite their relatively short evolutionary history. The European rabbit is one of the most recently domesticated animals, but exhibits distinct morphological, physiological, and behavioral differences from their wild conspecifics. A previous study revealed that sequence variants with striking allele frequency differences between wild and domestic rabbits were enriched in conserved noncoding regions, in the vicinity of genes involved in nervous system development. This suggests that a large proportion of the genetic changes targeted by selection during domestication might affect gene regulation. Here, we generated RNA-sequencing data for four brain regions (amygdala, hypothalamus, hippocampus, and parietal/temporal cortex) sampled at birth and revealed hundreds of differentially expressed genes (DEGs) between wild and domestic rabbits. DEGs in amygdala were significantly enriched for genes associated with dopaminergic function and all 12 DEGs in this category showed higher expression in domestic rabbits. DEGs in hippocampus were enriched for genes associated with ciliary function, all 21 genes in this category showed lower expression in domestic rabbits. These results indicate an important role of dopamine signaling and ciliary function in the evolution of tameness during rabbit domestication. Our study shows that gene expression in specific pathways has been profoundly altered during domestication, but that the majority of genes showing differential expression in this study have not been the direct targets of selection.

The chicken pan-genome reveals gene content variation and a promoter region deletion in IGF2BP1 affecting body size

Domestication and breeding have reshaped the genomic architecture of chicken, but the retention and loss of genomic elements during these evolutionary processes remain unclear. We present the first chicken pan-genome constructed using 664 individuals, which identified an additional ∼66.5 Mb sequences that are absent from the reference genome (GRCg6a). The constructed pan-genome encoded 20,491 predicated protein-coding genes, of which higher expression level are observed in conserved genes relative to dispensable genes. Presence/absence variation (PAV) analyses demonstrated that gene PAV in chicken was shaped by selection, genetic drift, and hybridization. PAV-based GWAS identified numerous candidate mutations related to growth, carcass composition, meat quality, or physiological traits. Among them, a deletion in the promoter region of IGF2BP1 affecting chicken body size is reported, which is supported by functional studies and extra samples. This is the first time to report the causal variant of chicken body size QTL located at chromosome 27 which was repeatedly reported. Therefore, the chicken pan-genome is a useful resource for biological discovery and breeding. It improves our understanding of chicken genome diversity and provides materials to unveil the evolution history of chicken domestication.

Domestic chicken diversity: Origin, distribution, and adaptation

Chicken is the most numerous among the domesticated livestock species. Across cultures, religions, and societies, chicken is widely accepted with little or no taboo compared to other domestic animals. Its adaptability to diverse environmental conditions and demonstrated potential for breeding improvement provide a unique genetic resource for addressing the challenges of food security in a world impacted by climatic change and human population growth. Recent studies, shedding new knowledge on the chicken genomes, have helped reconstruct its past evolutionary history. Here, we review the literature concerning the origin, dispersion, and adaptation of domestic chicken. We highlight the role of human and natural selection in shaping the diversity of the species and provide a few examples of knowledge gaps that may be the focus of future research.

Genome-wide detection of CNVs and their association with performance traits in broilers

Background

Copy number variations (CNVs) are a major type of structural genomic variants that underlie genetic architecture and phenotypic variation of complex traits, not only in humans, but also in livestock animals. We identified CNVs along the chicken genome and analyzed their association with performance traits. Genome-wide CNVs were inferred from Affymetrix® high density SNP-chip data for a broiler population. CNVs were concatenated into segments and association analyses were performed with linear mixed models considering a genomic relationship matrix, for birth weight, body weight at 21, 35, 41 and 42 days, feed intake from 35 to 41 days, feed conversion ratio from 35 to 41 days and, body weight gain from 35 to 41 days of age.

Results

We identified 23,214 autosomal CNVs, merged into 5042 distinct CNV regions (CNVRs), covering 12.84% of the chicken autosomal genome. One significant CNV segment was associated with BWG on GGA3 (q-value = 0.00443); one significant CNV segment was associated with BW35 (q-value = 0.00571), BW41 (q-value = 0.00180) and BW42 (q-value = 0.00130) on GGA3, and one significant CNV segment was associated with BW on GGA5 (q-value = 0.00432). All significant CNV segments were verified by qPCR, and a validation rate of 92.59% was observed. These CNV segments are located nearby genes, such as KCNJ11, MyoD1 and SOX6, known to underlie growth and development. Moreover, gene-set analyses revealed terms linked with muscle physiology, cellular processes regulation and potassium channels.

Conclusions

Overall, this CNV-based GWAS study unravels potential candidate genes that may regulate performance traits in chickens. Our findings provide a foundation for future functional studies on the role of specific genes in regulating performance in chickens.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-07676-1.

Mutations Upstream of the TBX5 and PITX1 Transcription Factor Genes Are Associated with Feathered Legs in the Domestic Chicken

Feathered leg is a trait in domestic chickens that has undergone intense selection by fancy breeders. Previous studies have shown that two major loci controlling feathered leg are located on chromosomes 13 and 15. Here, we present genetic evidence for the identification of candidate causal mutations at these loci. This was accomplished by combining classical linkage mapping using an experimental cross segregating for feathered leg and high-resolution identical-by-descent mapping using whole-genome sequence data from 167 samples of chicken with or without feathered legs. The first predicted causal mutation is a single-base change located 25 kb upstream of the gene for the forelimb-specific transcription factor TBX5 on chromosome 15. The second is a 17.7-kb deletion located ∼200 kb upstream of the gene for the hindlimb-specific transcription factor PITX1 on chromosome 13. These mutations are predicted to activate TBX5 and repress PITX1 expression, respectively. The study reveals a remarkable convergence in the evolution of the feathered-leg phenotype in domestic chickens and domestic pigeons, as this phenotype is caused by noncoding mutations upstream of the same two genes. Furthermore, the PITX1 causal variants are large overlapping deletions, 17.7 kb in chicken and 44 kb in pigeons. The results of the present study are consistent with the previously proposed model for pigeon that feathered leg is caused by reduced PITX1 expression and ectopic expression of TBX5 in hindlimb buds resulting in a shift of limb identity from hindlimb to more forelimb-like identity.

Comparative analysis of hypothalamus transcriptome between laying hens with different egg-laying rates

Egg-laying performance is one of the most important economic traits in the poultry industry. Commercial layers can lay one egg almost every day during their peak-laying period. However, many Chinese indigenous chicken breeds show a relatively low egg-laying rate, even during their peak-laying period. To understand what makes the difference in egg production, we compared the hypothalamus transcriptome profiles of Lushi blue-shelled-egg chickens (LBS), a Chinese indigenous breed with low egg-laying rate and Rhode Island Red chickens (RIR), a commercial layer with relatively high egg-laying rate using RNA-seq. A total of 753 differentially expressed genes (DEGs) were obtained. Of these DEGs, 38 genes were enriched in 2 Gene Ontology (GO) terms, namely reproduction term and the reproductive process term, and 6 KEGG pathways, namely Wnt signaling pathway, Oocyte meiosis, GnRH signaling pathway, Thyroid hormone signaling pathway, Thyroid hormone synthesis and MAPK signaling pathway, which have been long known to be involved in egg production regulation. To further determine the core genes from the 38 DEGs, protein-protein interaction (PPI) network, co-expression network and transcriptional regulatory network analyses were carried out. After integrated analysis and experimental validation, 4 core genes including RAC1, MRE11A, MAP7 and SOX5 were identified as the potential core genes that are responsible for the laying-rate difference between the 2 breeds. These findings paved the way for future investigating the mechanism of egg-laying regulation and enriched the chicken reproductive regulation theory.

Copy number variation: Characteristics, evolutionary and pathological aspects

Copy number variants (CNVs) were the subject of extensive research in the past years. They are common features of the human genome that play an important role in evolution, contribute to population diversity, development of certain diseases, and influence host–microbiome interactions. CNVs have found application in the molecular diagnosis of many diseases and in non-invasive prenatal care, but their full potential is only emerging. CNVs are expected to have a tremendous impact on screening, diagnosis, prognosis, and monitoring of several disorders, including cancer and cardiovascular disease. Here, we comprehensively review basic definitions of the term CNV, outline mechanisms and factors involved in CNV formation, and discuss their evolutionary and pathological aspects. We suggest a need for better defined distinguishing criteria and boundaries between known types of CNVs.

Copy Number Variants in Four Italian Turkey Breeds

Simple Summary

Hybrid Turkey selection is focusing on meat production traits characterized by high genetic heritability; the strong directional selection is well known to produce a constant loss in genetic diversity. Genetic characterization is one of the essential activities in the management of populations at risk of extinction. In addition, the genetic structure at the population level and the relationships between individuals are nowadays analysable at the genomic level. In this paper, the genome of 4 different Italian turkey breeds included in the Autochthonous Italian Poultry Breeds Register are analysed in order to obtain a genome-wide Copy Number Variant scan to ameliorate the existing knowledge of the genomic structure of Italian local turkey breeds. Differences have been described at genomic level for physiological, reproductive, and behavioral traits. The analyzed breeds are clearly distinguishable at the genomic level, and their relationships are clearly linked to their geographical origin and to the history of the rural structure of their developing regions. Genome information based on Copy Number Variant (CNV) detection has generated important information in this study concerning the uniqueness of the Italian local turkey breeds.

Abstract

Heritage breeds can be considered a genetic reservoir of genetic variability to be conserved and valorized considering their historical, cultural, and adaptive characteristics and possibly for their high potential in commercial hybrid genetic improvement by gene introgression. The aim of the present research is to investigate via Copy Number Variant (CNVs) the genomic makeup of 4 Italian autochthonous turkey breeds (Bronzato Comune—BrCI, 24; Ermellinato di Rovigo—ErRo, 24; Parma e Piacenza—PrPc, 25; Romagnolo—RoMa, 29). CNVs detection was performed using two different software and an interbreed CNVs comparison was carried out. A total of 1077 CNVs were identified in 102 turkeys, summarized into 519 CNV regions (CNVRs), which resulted after merging in 101 and 18 breed and shared regions. Biodiversity was analyzed using the effective information supplied by CNVs analysis, and BrCI and ErRo were characterized by a low mapped CNV number. Differences were described at a genomic level related to physiological, reproductive, and behavioral traits. The comparison with other three Italian turkey breeds (Brianzolo, Colle Euganei, and Nero Italiano) using a CNV data set available in the literature showed high clustering properties at the genomic level, and their relationships are strictly linked to the geographical origin and to the history of the rural structure of their native regions.

Polymorphisms of AMY1A gene and their association with growth, carcass traits and feed intake efficiency in chickens

Investigations on the association between chicken traits and genetic variations can provide basic information to improve production performance in chickens. In our previous work, we genotyped 450 male chickens with a 600 K SNP array [1] and found that several SNPs in the genomic regions of the amylase alpha 1A (AMY1A) gene were significantly associated with feed intake efficiency and carcass traits. Given the lower accuracy of the SNP array, we performed direct sequencing with male and female chickens to further test chicken AMY1A polymorphisms and investigate their association with 17 traits in chickens. The results showed that 7 SNPs in the 5' flanking region, exon, intron and 3' UTR (3' untranslated region) of AMY1A, were significantly associated with daily gain (DG), average daily feed intake (ADFI), leg muscle weight (LMW) and abdominal fat (AF) (p < 0.05). Additionally, the haplotypes based on three SNPs, rs15910189, rs314354067 and rs316026696, showed significant associations with DG (p < 0.01), ADFI and AF (p < 0.05). To better understand the transcriptional regulation of AMY1A, we cloned its 5' flanking region and found that the SNPs rs316436216 and rs314213090 which might change the transcriptional regulator binding sites, were in the suppressor and enhancer regions, respectively. In addition, luciferase assays revealed that the SNP rs314613110 in the 3' UTR influenced the binding of the miRNA gga-miR-1764-3p. To validate whether there is any copy number variation in AMY1A in our population, we performed a genome-wide assessment of CNVs through whole-genome resequencing data. However, no CNV was found in AMY1A in our population, which is different from the increased copy number of AMY1A found in humans who consume a high-starch diet. Therefore, the present study provides substantial evidence for the association of AMY1A polymorphisms with growth traits and feed intake efficiency, which might contribute to chicken breeding programs.

A molecular marker of milk composition traits in NCAM2 gene of Chinese Holstein

The aim of this study was to detect the novel copy number variation (CNV) locus of NCAM2 gene in Chinese Holstein, and to analyze the effect of the novel CNV locus in NCAM2 gene on milk composition traits. The novel CNV locus of NCAM2 gene in 310 Chinese Holstein was detected by real-time quantitative fluorescent PCR (qPCR) and association analysis was performed between the novel CNV locus in NCAM2 gene and milk composition traits in Chinese Holstein. There are three CNV types of NCAM2 gene in Chinese Holstein: gain (increased copy number), median (normal copy number) and loss (deleted copy number). Statistical analysis revealed that there was a significant association between CNV types and milk fat rate (p < 0.05). Moreover, we also discovered that the milk production and milk protein rate of gain type is higher than that of loss type, but that of mediate type is lower than that of loss type. However, in terms of somatic cell score, loss type is higher than that of gain type, but that of mediate type is lower than that of gain type. These observations suggested that gain type can be used as a candidate molecular genetic marker of milk fat rate.HighlightsThe CNVs of the NCAM2 gene were detected and validated in Chinese Holstein.The type of CNV was successfully implemented using qPCR.The statistical analysis indicated that the CNV of the NCAM2 gene are significantly associated with milk fat rate.