The crest phenotype in chicken is associated with ectopic expression of HOXC8 in cranial skin

Whole-Genome Sequencing for Identifying Candidate Genes Related to the Special Phenotypes of the Taihu Dianzi Pigeon

The Taihu Dianzi pigeon is a breed native to China, and its special piebalding, crest, and polydactyly phenotypes are the result of artificial and natural selection. Here, we analyzed the genetic differences among three kinds of pigeons with different phenotypes at the genomic level. A selective sweep was conducted based on the fixation index (FST) and nucleotide diversity (π) ratio, and the results revealed that MC1R was related to the formation of the distinctive piebalding of the Taihu Dianzi pigeon. Combined with the results of genome-wide association studies, we identified candidate genes associated with the crest (SMYD and STOX2) and polydactyly (SLC52A3 and ANGPT4). The candidate genes identified in this study and their variants may be useful for understanding the genetic mechanism underlying the special phenotypes of the Taihu Dianzi pigeon. This study provides new insights into the genetic factors that may influence the formation of the special piebalding, crest, and polydactyly characteristics in pigeons.

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.

Chicken HOXC8 and HOXC10 genes may play a role in the altered skull morphology associated with the Crest phenotype

One of the most intriguing traits found in domestic chickens is the Crest phenotype. This trait, characterized by a tuft of elongated feathers sprouted from the head, is found in breeds such as Polish chickens and Silkie chickens. Moreover, some crested chicken breeds also exhibit a protuberance in their anterodorsal skull region. Previous studies have strived to identify the causative factors of this trait. This study aimed to elucidate the role of chicken HOXC8 and HOXC10 in the formation of the Crest phenotype. We explored the effect of ectopic expression of HOXC8 or HOXC10 on the chicken craniofacial morphology using the RCAS retrovirus transformation system. Microcomputed tomography scanning was conducted to measure the 3D structure of the cranial bone of transgenic embryos for geometric morphometric analysis. We found that the ectopic expression of HOXC8 or HOXC10 in chicken heads caused mild morphological changes in the skull compared with the GFP-transgenic control group. Geometric morphometric analysis showed that HOXC8 and HOXC10 transgenic groups expressed a mild upward shape change in the frontal region of the skull compared with the control group, which is similar to what is seen in the crested chicken breeds. In conclusion, this study supports findings in previous studies in which HOX genes play a role in the formation of the altered skull morphology related to the Crest phenotype. It also supports that mutations in HOX genes may contribute to intra- and inter-specific variation in morphological traits in vertebrates.

Dumbbell-shaped brains of Polish crested chickens as a model system for the evolution of novel brain morphologies

The evolutionary history of vertebrates is replete with emergence of novel brain morphologies, including the origin of the human brain. Existing model organisms and toolkits for investigating drivers of neuroanatomical innovations have largely proceeded on mammals. As such, a compelling non-mammalian model system would facilitate our understanding of how unique brain morphologies evolve across vertebrates. Here, we present the domestic chicken breed, white crested Polish chickens, as an avian model for investigating how novel brain morphologies originate. Most notably, these crested chickens exhibit cerebral herniation from anterodorsal displacement of the telencephalon, which results in a prominent protuberance on the dorsal aspect of the skull. We use a high-density geometric morphometric approach on cephalic endocasts to characterize their brain morphology. Compared with standard white Leghorn chickens (WLCs) and modern avian diversity, the results demonstrate that crested chickens possess a highly variable and unique overall brain configuration. Proportional sizes of neuroanatomical regions are within the observed range of extant birds sampled in this study, but Polish chickens differ from WLCs in possessing a relatively larger cerebrum and smaller cerebellum and medulla. Given their accessibility, phylogenetic proximity, and unique neuroanatomy, we propose that crested breeds, combined with standard chickens, form a promising comparative system for investigating the emergence of novel brain morphologies.

Large-scale detection and characterization of interchromosomal rearrangements in normozoospermic bulls using massive genotype and phenotype data sets

In this paper, we developed a highly sensitive approach to detect interchromosomal rearrangements in cattle by searching for abnormal linkage disequilibrium patterns between markers located on different chromosomes in large paternal half-sib families genotyped as part of routine genomic evaluations. We screened 5571 families of artificial insemination sires from 15 breeds and revealed 13 putative interchromosomal rearrangements, 12 of which were validated by cytogenetic analysis and long-read sequencing. These consisted of one Robertsonian fusion, 10 reciprocal translocations, and the first case of insertional translocation reported in cattle. Taking advantage of the wealth of data available in cattle, we performed a series of complementary analyses to define the exact nature of these rearrangements, investigate their origins, and search for factors that may have favored their occurrence. We also evaluated the risks to the livestock industry and showed significant negative effects on several traits in the sires and in their balanced or aneuploid progeny compared with wild-type controls. Thus, we present the most comprehensive and thorough screen for interchromosomal rearrangements compatible with normal spermatogenesis in livestock species. This approach is readily applicable to any population that benefits from large genotype data sets, and will have direct applications in animal breeding. Finally, it also offers interesting prospects for basic research by allowing the detection of smaller and rarer types of chromosomal rearrangements than GTG banding, which are interesting models for studying gene regulation and the organization of genome structure.

Uganda chicken genetic resources: I. phenotypic and production characteristics

The extent of diversity in the indigenous chicken breeds of Uganda was assessed for their potential utilisation in breeding programmes. A total of 293 indigenous-chicken-keeping households in villages across 35 districts forming 12 sub-regions of the four regions were randomly sampled for 586 mature chickens of both sexes. While only 20.8% of households were headed by women, 40.6% of indigenous chicken keepers were women. The production objectives mainly focused on chickens as sources of income from sales and household food. The chickens were predominantly managed in a scavenging (94.2%) feeding system in a mainly (96.9%) mixed crop-livestock system. The average flock size was 19.80 ± 1.21 chickens with 3.83 ± 0.29 laying hens, each producing an average of 13.41 ± 0.20 eggs/clutch and 40.3 ± 0.6 eggs/annum of 5.20 ± 0.03-month egg production age. Normal-feather strains predominated (>90%), with scattered incidences of naked neck, frizzles, polydactyl, and ptilopody traits in both sexes. Dark (49.0% hen; 43.8% cock) and white (38.3% hen; 42.4% cock) skin colours were most common among the chickens compared to yellow skin. However, yellow-coloured shanks were proportionally the most observed (41% cock; 29% hen). Orange and brown iris (eye) colours were the most common in both sexes. The hens commonly had small round earlobes with varying colours, while cocks had large oval-shaped, mainly red (70%) earlobes. The single-comb type was dominant in both sexes, with wattles almost universally present. Frizzle and polydactyl allele frequencies were significantly lower (p < 0.05) than the expected Mendelian proportions, indicating a possible state of endangerment. Meanwhile, the estimated allele frequencies of ptilopody, tufted-crest, and rose comb alleles in the population were similar (p > 0.05) to the expected Mendelian frequencies. However, these strains did not show any significant (p > 0.05) influence on the body weight or the linear morphometric estimates except for being marginally higher than the normal strains. The phenotypic correlations of body weight and morphometric traits ranged from 0.457 to 0.668 and 0.292 to 0.454 in cocks and hens, respectively. These findings provide hints about the prospects for improved performance with modifications in the production environment. The wide phenotypic diversity would support management efforts for their sustainable utilisation and preservation.

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.

Identification of Genes Associated with Crest Cushion Development in the Chinese Crested Duck

Simple Summary

The crest cushion is a phenotypic appendage observed in most birds, and its appearance differs according to the species. However, the mechanism underlying the formation of the crest cushion and the changes in the expression of the associated genes during development has not been elucidated. We aimed to study the differential expression of selected genes in the Chinese crested duck to assess the genes involved in crest cushion formation and their expression. Our results show that the expression of genes belonging to the homeobox family was significantly altered during the various developmental stages, highlighting their role in the development of the crest cushion. This study elucidated a method to assess the molecular mechanism involved in the formation of the crest cushion and to assess the changes in the gene expression at the genome level.

Abstract

The crest trait is a specific and widely distributed phenotype in birds. However, the shape and function vary in different species of birds. To understand the mechanism of crest formation, the present study used RNA sequencing and weighted gene co-expression network analysis (WGCNA) to identify the crest-cushion-associated genes in the Chinese crested (CC) duck. As a result, 28, 40, 32, 33, and 126 differentially expressed genes (DEGs) were identified between CC and cherry valley (CV) ducks at the embryonic days (E)15, E22, E28, D7 (7 days old), and D42 stages, respectively. In addition, the results of WGCNA show that 3697 (turquoise module), 485 (green-yellow module), 687 (brown module), 205 (red module), and 1070 (yellow module) hub genes were identified in the E15, E22, E28, D7, and D42 stages, respectively. Based on the results of DEGs and WGCNA Venn analysis, three, two, zero, one, and seven genes were found to be associated with crest cushion formation at the E15, E22, E28, D7, and D42 stages, respectively. The expression of all the associated genes and some DEGs was verified by real-time quantitative polymerase chain reaction. In conclusion, this study provided an approach revealing the molecular mechanisms underlying the crested trait development.

Potassium channel-driven bioelectric signalling regulates metastasis in triple-negative breast cancer

BACKGROUND

There is a critical need to better understand the mechanisms that drive local cell invasion and metastasis to develop new therapeutics targeting metastatic disease. Bioelectricity is an important mediator of cellular processes and changes in the resting membrane potential (RMP) are associated with increased cancer cell invasion. However, whether the RMP can be used to target invading cancer cells is unknown.

METHODS

We employed both genetic and pharmacological manipulation of potassium channel activity and characterized the effects on breast cancer cell migration and invasion in vitro, and metastasis in an animal model of breast cancer.

FINDINGS

Our data demonstrate that altering the RMP of triple-negative breast cancer (TNBC) cells by manipulating potassium channel expression increases in vitro invasion, in vivo tumour growth and metastasis, and is accompanied by changes in gene expression associated with cell adhesion.

INTERPRETATION

We describe a novel mechanism for RMP-mediated cell migration involving cadherin-11 and the MAPK pathway. Importantly, we identify a new strategy to target metastatic TNBC in vivo by repurposing an FDA-approved potassium channel blocker. Our results demonstrate that bioelectricity regulates cancer cell invasion and metastasis which could lead to a new class of therapeutics for patients with metastatic disease.

FUNDING

This work was supported by the National Institutes of Health (R00-CA207866 to M.J.O.), Tufts University (Start-up funds from the School of Engineering to M.J.O., Tufts Collaborates Award to M.J.O. and M.L.), Allen Discovery centre program (Paul G. Allen Frontiers Group (12,171) to M.L.), and Breast Cancer Alliance Young Investigator Grant to M.J.O, Laidlaw Scholar funding to D.S. M.L. also gratefully acknowledges support of the Barton Family Foundation.

High Genetic Diversity but Absence of Population Structure in Local Chickens of Sri Lanka Inferred by Microsatellite Markers

Local chicken populations belonging to five villages in two geographically separated provinces of Sri Lanka were analyzed using 20 microsatellite markers to determine the genetic diversity of local chickens. Population genetic parameters were estimated separately for five populations based on geographic locations and for eight populations based on phenotypes, such as naked neck, long legged, crested or crown, frizzle feathered, Giriraj, commercial layer, crossbreds, and non-descript chicken. The analysis revealed that there was a high genetic diversity among local chickens with high number of unique alleles, mean number of alleles per locus (MNA), and total number of alleles per locus per population. A total of 185 microsatellite alleles were detected in 192 samples, indicating a high allelic diversity. The MNA ranged from 8.10 (non-descript village chicken) to 3.50 (Giriraj) among phenotypes and from 7.30 (Tabbowa) to 6.50 (Labunoruwa) among village populations. In phenotypic groups, positive inbreeding coefficient (F IS) values indicated the existence of population substructure with evidence of inbreeding. In commercial layers, a high expected heterozygosity He = 0.640 ± 0.042) and a negative F IS were observed. The positive F IS and high He estimates observed in village populations were due to the heterogeneity of samples, owing to free mating facilitated by communal feeding patterns. Highly admixed nature of phenotypes was explained as a result of rearing many phenotypes by households (58%) and interactions of chickens among neighboring households (53%). A weak substructure was evident due to the mating system, which disregarded the phenotypes. Based on genetic distances, crown chickens had the highest distance to other phenotypes, while the highest similarity was observed between non-descript village chickens and naked neck birds. The finding confirms the genetic wealth conserved within the populations as a result of the breeding system commonly practiced by chicken owners. Thus, the existing local chicken populations should be considered as a harbor of gene pool, which can be readily utilized in developing locally adapted and improved chicken breeds in the future.

The crest phenotype in domestic chicken is caused by a 197 bp duplication in the intron of HOXC10

The Crest mutation in chicken shows incomplete dominance and causes a spectacular phenotype in which the small feathers normally present on the head are replaced by much larger feathers normally present only in dorsal skin. Using whole-genome sequencing, we show that the crest phenotype is caused by a 197 bp duplication of an evolutionarily conserved sequence located in the intron of HOXC10 on chromosome 33. A diagnostic test showed that the duplication was present in all 54 crested chickens representing eight breeds and absent from all 433 non-crested chickens representing 214 populations. The mutation causes ectopic expression of at least five closely linked HOXC genes, including HOXC10, in cranial skin of crested chickens. The result is consistent with the interpretation that the crest feathers are caused by an altered body region identity. The upregulated HOXC gene expression is expanded to skull tissue of Polish chickens showing a large crest often associated with cerebral hernia, but not in Silkie chickens characterized by a small crest, both homozygous for the duplication. Thus, the 197 bp duplication is required for the development of a large crest and susceptibility to cerebral hernia because only crested chicken show this malformation. However, this mutation is not sufficient to cause herniation because this malformation is not present in breeds with a small crest, like Silkie chickens.

Shifts in growth, but not differentiation, foreshadow the formation of exaggerated forms under chicken domestication

Domestication provides an outstanding opportunity for biologists to explore the underpinnings of organismal diversification. In domesticated animals, selective breeding for exaggerated traits is expected to override genetic correlations that normally modulate phenotypic variation in nature. Whether this strong directional selection affects the sequence of tightly synchronized events by which organisms arise (ontogeny) is often overlooked. To address this concern, we compared the ontogeny of the red junglefowl (RJF) (Gallus gallus) to four conspecific lineages that underwent selection for traits of economic or ornamental value to humans. Trait differentiation sequences in embryos of these chicken breeds generally resembled the representative ancestral condition in the RJF, thus revealing that early ontogeny remains highly canalized even during evolution under domestication. This key finding substantiates that the genetic cost of domestication does not necessarily compromise early ontogenetic steps that ensure the production of viable offspring. Instead, disproportionate beak and limb growth (allometry) towards the end of ontogeny better explained phenotypes linked to intense selection for industrial-scale production over the last 100 years. Illuminating the spatial and temporal specificity of development is foundational to the enhancement of chicken breeds, as well as to ongoing research on the origins of phenotypic variation in wild avian species.

Integrative analysis of histomorphology, transcriptome and whole genome resequencing identified DIO2 gene as a crucial gene for the protuberant knob located on forehead in geese

Background

During domestication, remarkable changes in behavior, morphology, physiology and production performance have taken place in farm animals. As one of the most economically important poultry, goose owns a unique appearance characteristic called knob, which is located at the base of the upper bill. However, neither the histomorphology nor the genetic mechanism of the knob phenotype has been revealed in geese.

Results

In the present study, integrated radiographic, histological, transcriptomic and genomic analyses revealed the histomorphological characteristics and genetic mechanism of goose knob. The knob skin was developed, and radiographic results demonstrated that the knob bone was obviously protuberant and pneumatized. Histologically, there were major differences in structures in both the knob skin and bone between geese owing knob (namely knob-geese) and those devoid of knob (namely non-knob geese). Through transcriptome analysis, 592 and 952 genes differentially expressed in knob skin and bone, and significantly enriched in PPAR and Calcium pathways in knob skin and bone, respectively, which revealed the molecular mechanisms of histomorphological differences of the knob between knob- and non-knob geese. Furthermore, integrated transcriptomic and genomic analysis contributed to the identification of 17 and 21 candidate genes associated with the knob formation in the skin and bone, respectively. Of them, DIO2 gene could play a pivotal role in determining the knob phenotype in geese. Because a non-synonymous mutation (c.642,923 G > A, P265L) changed DIO2 protein secondary structure in knob geese, and Sanger sequencing further showed that the AA genotype was identified in the population of knob geese, and was prevalent in a crossing population which was artificially selected for 10 generations.

Conclusions

This study was the first to uncover the knob histomorphological characteristics and genetic mechanism in geese, and DIO2 was identified as the crucial gene associated with the knob phenotype. These data not only expand and enrich our knowledge on the molecular mechanisms underlying the formation of head appendages in both mammalian and avian species, but also have important theoretical and practical significance for goose breeding.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-07822-9.

RNA-sequence reveals differentially expressed genes affecting the crested trait of Wumeng crested chicken

Wumeng crested chicken has a cluster of slender feathers on its head, and the underlying skull region exhibits an obvious tumor-like protrusion. This is the typical skull structure of crested chickens. The associated regulatory genes are located on autosomes and are incompletely dominant. This trait is related to brain herniation, but the genetic mechanisms of its formation and development are unclear. In this study, RNA sequencing (RNA-Seq) analysis was conducted on 6 skull tissue samples from 3 Wumeng crested chickens with prominent skull protrusions and 3 without a prominent skull protrusion phenotype. A total of 46,376,934 to 43,729,046 clean reads were obtained, the percentage of uniquely mapped reads compared with the reference genome was between 89.73%-91.00%, and 39,795,458-41,836,502 unique reads were obtained. Among different genomic regions, the highest frequency of sequencing reads occurred in exon regions (85.44-88.28%). Additionally, a total of 423 new transcripts and 26,999 alternative splicings (AS) events were discovered in this sequencing analysis. This study identified 1,089 differentially expressed genes (DEGs), among which 485 were upregulated and 604 were downregulated. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses indicated that the DEGs were enriched in terms related to signal transduction, cell development, cell differentiation, the lysosome, serine, and threonine metabolism, and the interaction of cytokines with cytokine receptors. Based on the comprehensive analysis of DEGs combined with reported quantitative trait loci (QTLs), the expression of BMP2, EPHA3, EPHB1, HOXC6, SCN2B, BMP7, and HOXC10 was verified by real-time quantitative polymerase chain reaction (qRT-PCR). The qRT-PCR results were consistent with the RNA-Seq results, indicating that these 7 genes may be candidates genes regulating the crested trait.

The Effects of Domestication on the Brain and Behavior of the Chicken in the Light of Evolution

The avian class is characterized by particularly strong variability in their domesticated species. With more than 250 breeds and highly efficient commercial lines, domestic chickens represent the outcome of a really long period of artificial selection. One characteristic of domestication is the alterations in brain size and brain composition. The influence of domestication on brain morphology has been reviewed in the past, but mostly with a focus on mammals. Studies on avian species have seldom been taken into account. In this review, we would like to give an overview about the changes and variations in (brain) morphology and behavior in the domestic chicken, taking into consideration the constraints of evolutionary theory and the sense or nonsense of excessive artificial selection.

Parallel Genetic Origin of Foot Feathering in Birds

Understanding the genetic basis of similar phenotypes shared between lineages is a long-lasting research interest. Even though animal evolution offers many examples of parallelism, for many phenotypes little is known about the underlying genes and mutations. We here use a combination of whole-genome sequencing, expression analyses, and comparative genomics to study the parallel genetic origin of ptilopody (Pti) in chicken. Ptilopody (or foot feathering) is a polygenic trait that can be observed in domesticated and wild avian species and is characterized by the partial or complete development of feathers on the ankle and feet. In domesticated birds, ptilopody is easily selected to fixation, though extensive variation in the type and level of feather development is often observed. By means of a genome-wide association analysis, we identified two genomic regions associated with ptilopody. At one of the loci, we identified a 17-kb deletion affecting PITX1 expression, a gene known to encode a transcription regulator of hindlimb identity and development. Similarly to pigeon, at the second loci, we observed ectopic expression of TBX5, a gene involved in forelimb identity and a key determinant of foot feather development. We also observed that the trait evolved only once as foot-feathered birds share the same haplotype upstream TBX5. Our findings indicate that in chicken and pigeon ptilopody is determined by the same set of genes that affect similar molecular pathways. Our study confirms that ptilopody has evolved through parallel evolution in chicken and pigeon.

Deciphering the Forebrain Disorder in a Chicken Model of Cerebral Hernia

Cerebral hernia in crested chicken has been characterized as the protrusion of cerebral hemispheres into the unsealed skull for hundreds of years, since Charles Darwin. The development of deformed forebrain (telencephalon) of cerebral hernia remains largely unknown. Here, the unsealed frontal skull combined with misplaced sphenoid bone was observed and potentially associated with brain protuberance. The shifted pallidum, elongated hippocampus, expanded mesopallium and nidopallium, and reduced hyperpallium were observed in seven regions of the malformed telencephalon. The neurons were detected with nuclear pyknosis and decreased density. Astrocytes showed uneven distribution and disordered protuberances in hyperpallium and hippocampus. Transcriptome analyses of chicken telencephalon (cerebral hernia vs. control) revealed 547 differentially expressed genes (DEGs), mainly related to nervous system development, and immune system processes, including astrocyte marker gene GFAP, and neuron and astrocyte developmental gene S100A6. The upregulation of GFAP and S100A6 genes in abnormal telencephalon was correlated with reduced DNA methylation levels in the promoter regions. The morphological, cellular, and molecular variations in the shape, regional specification, and cellular states of malformed telencephalon potentially participate in brain plasticity and previously reported behavior changes. Chickens with cerebral hernia might be an interesting and valuable disease model to further explore the recognition, diagnosis, and therapy of cerebral hernia development of crested chickens and other species.

Whole-genome resequencing reveals genetic indels of feathered-leg traits in domestic chickens

Whole-genome resequencing provides the opportunity to explore the genomic variations and pave way for further functional assays to map the economical trait loci. In this study, we sequenced the genomes of mixed chicken samples from a full-sib family, with feathered and unfeathered legs at an average effective depth of 4.43×, using Illumina Hiseq 2000 instruments. Over 2.1 million nonredundant short indels (1-71 bp) were obtained. Among them, 16,375 common indels that were polymorphic between the comparison groups were revealed for further analysis. The majority of the common differential indels (76.52%) were novel. Follow-up validation assays confirmed that 80% randomly selected indels represented true variations. The indels were annotated based on the chicken genome sequence assembly. As a result, 16,375 indels were found to be located within 2756 annotated genes, with only 33 (0.202%) located in exons. By integrated analysis of the 2756 genes with gene function and known quantitative trait loci, we identified a total of 24 promising candidate genes potentially affecting feathered-leg trait, i.e. FGF1, FGF4, FGF10, FGFR1, FRZB, WNT1, WNT3A, WNT11, PCDH1, PCDH10, PCDH19, SOX3, BMP2, NOTCH2, TGF-β2, DLX5, REPS2, SCN3B, TCF20, FGF3, FSTL1, WNT7B, ELOVL2 and FGF8. Our findings provide a basis for further study and reveal key genes for feathered-leg trait in chickens.

Genetic and Molecular Basis of Feather Diversity in Birds

Feather diversity is striking in many aspects. Although the development of feather has been studied for decades, genetic and genomic studies of feather diversity have begun only recently. Many questions remain to be answered by multidisciplinary approaches. In this review, we discuss three levels of feather diversity: Feather morphotypes, intraspecific variations, and interspecific variations. We summarize recent studies of feather evolution in terms of genetics, genomics, and developmental biology and provide perspectives for future research. Specifically, this review includes the following topics: 1) Diversity of feather morphotype; 2) feather diversity among different breeds of domesticated birds, including variations in pigmentation pattern, in feather length or regional identity, in feather orientation, in feather distribution, and in feather structure; and 3) diversity of feathers among avian species, including plumage color and morph differences between species and the regulatory differences in downy feather development between altricial and precocial birds. Finally, we discussed future research directions.

Dynamic transcriptome profiling towards understanding the morphogenesis and development of diverse feather in domestic duck

Background

Feathers with complex and fine structure are hallmark avian integument appendages, which have contributed significantly to the survival and breeding for birds. Here, we aimed to explore the differentiation, morphogenesis and development of diverse feathers in the domestic duck.

Results

Transcriptome profiles of skin owing feather follicle from two body parts at three physiological stages were constructed to understand the molecular network and excavate the candidate genes associated with the development of plumulaceous and flight feather structures. The venn analysis of differentially expressed genes (DEGs) between abdomen and wing skin tissues at three developmental stages showed that 38 genes owing identical differentially expression pattern. Together, our data suggest that feather morphological and structural diversity can be possibly related to the homeobox proteins. The key series-clusters, many candidate biological processes and genes were identified for the morphogenesis, growth and development of two feather types. Through comparing the results of developmental transcriptomes from plumulaceous and flight feather, we found that DEGs belonging to the family of WNT, FGF and BMP have certain differences; even the consistent DEGs of skin and feather follicle transcriptomes from abdomen and wing have the different expression patterns.

Conclusions

Overall, this study detected many functional genes and showed differences in the molecular mechanisms of diverse feather developments. The findings in WNT, FGF and BMP, which were consistent with biological experiments, showed more possible complex modulations. A correlative role of HOX genes was also suggested but future biological verification experiments are required. This work provided valuable information for subsequent research on the morphogenesis of feathers.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-4778-7) contains supplementary material, which is available to authorized users.

Genomic determinants of epidermal appendage patterning and structure in domestic birds

Variation in regional identity, patterning, and structure of epidermal appendages contributes to skin diversity among many vertebrate groups, and is perhaps most striking in birds. In pioneering work on epidermal appendage patterning, John Saunders and his contemporaries took advantage of epidermal appendage diversity within and among domestic chicken breeds to establish the importance of mesoderm-ectoderm signaling in determining skin patterning. Diversity in chickens and other domestic birds, including pigeons, is driving a new wave of research to dissect the molecular genetic basis of epidermal appendage patterning. Domestic birds are not only outstanding models for embryonic manipulations, as Saunders recognized, but they are also ideal genetic models for discovering the specific genes that control normal development and the mutations that contribute to skin diversity. Here, we review recent genetic and genomic approaches to uncover the basis of epidermal macropatterning, micropatterning, and structural variation. We also present new results that confirm expression changes in two limb identity genes in feather-footed pigeons, a case of variation in appendage structure and identity.

Pigeonetics takes flight: Evolution, development, and genetics of intraspecific variation

Intensive artificial selection over thousands of years has produced hundreds of varieties of domestic pigeon. As Charles Darwin observed, the morphological differences among breeds can rise to the magnitude of variation typically observed among different species. Nevertheless, different pigeon varieties are interfertile, thereby enabling forward genetic and genomic approaches to identify genes that underlie derived traits. Building on classical genetic studies of pigeon variation, recent molecular investigations find a spectrum of coding and regulatory alleles controlling derived traits, including plumage color, feather growth polarity, and limb identity. Developmental and genetic analyses of pigeons are revealing the molecular basis of variation in a classic example of extreme intraspecific diversity, and have the potential to nominate genes that control variation among other birds and vertebrates in general.

A Complex Structural Variation on Chromosome 27 Leads to the Ectopic Expression of HOXB8 and the Muffs and Beard Phenotype in Chickens

Muffs and beard (Mb) is a phenotype in chickens where groups of elongated feathers gather from both sides of the face (muffs) and below the beak (beard). It is an autosomal, incomplete dominant phenotype encoded by the Muffs and beard (Mb) locus. Here we use genome-wide association (GWA) analysis, linkage analysis, Identity-by-Descent (IBD) mapping, array-CGH, genome re-sequencing and expression analysis to show that the Mb allele causing the Mb phenotype is a derived allele where a complex structural variation (SV) on GGA27 leads to an altered expression of the gene HOXB8. This Mb allele was shown to be completely associated with the Mb phenotype in nine other independent Mb chicken breeds. The Mb allele differs from the wild-type mb allele by three duplications, one in tandem and two that are translocated to that of the tandem repeat around 1.70 Mb on GGA27. The duplications contain total seven annotated genes and their expression was tested during distinct stages of Mb morphogenesis. A continuous high ectopic expression of HOXB8 was found in the facial skin of Mb chickens, strongly suggesting that HOXB8 directs this regional feather-development. In conclusion, our results provide an interesting example of how genomic structural rearrangements alter the regulation of genes leading to novel phenotypes. Further, it again illustrates the value of utilizing derived phenotypes in domestic animals to dissect the genetic basis of developmental traits, herein providing novel insights into the likely role of HOXB8 in feather development and differentiation.

Genetic variation is a key part for the study of evolution, development and differentiation. In domestic animals, many breeds display striking phenotypes that differentiate them from their wild ancestors. Several of these have been related to structural variations, including Fibromelanosis and Rose-comb in chickens, Double-muscled and Osteopetrosis in cattle, Cone degeneration in dogs, and White coat color in pigs. The feather is a type of skin appendages that exists in multiple variants on different body parts, and the derived feathering phenotypes in domestic birds are perfect resources to decipher the mechanisms regulating feather development and differentiation. Here we study the genetics of the Muffs and beard trait, a variant that alters the feather development in the facial area of chickens. We show that this phenotype is associated with a genomic structural variant that leads to an ectopic expression of HOXB8 in the facial skin during feather development. This is thus another example of how structural variants in the genome lead to novel, derived phenotypic changes in domestic animals and suggests an important role for HOXB8 in feather development.

The old and new face of craniofacial research: How animal models inform human craniofacial genetic and clinical data

The craniofacial skeletal structures that comprise the human head develop from multiple tissues that converge to form the bones and cartilage of the face. Because of their complex development and morphogenesis, many human birth defects arise due to disruptions in these cellular populations. Thus, determining how these structures normally develop is vital if we are to gain a deeper understanding of craniofacial birth defects and devise treatment and prevention options. In this review, we will focus on how animal model systems have been used historically and in an ongoing context to enhance our understanding of human craniofacial development. We do this by first highlighting "animal to man" approaches; that is, how animal models are being utilized to understand fundamental mechanisms of craniofacial development. We discuss emerging technologies, including high throughput sequencing and genome editing, and new animal repository resources, and how their application can revolutionize the future of animal models in craniofacial research. Secondly, we highlight "man to animal" approaches, including the current use of animal models to test the function of candidate human disease variants. Specifically, we outline a common workflow deployed after discovery of a potentially disease causing variant based on a select set of recent examples in which human mutations are investigated in vivo using animal models. Collectively, these topics will provide a pipeline for the use of animal models in understanding human craniofacial development and disease for clinical geneticist and basic researchers alike.

Domestic animals as models for biomedical research

Domestic animals are unique models for biomedical research due to their long history (thousands of years) of strong phenotypic selection. This process has enriched for novel mutations that have contributed to phenotype evolution in domestic animals. The characterization of such mutations provides insights in gene function and biological mechanisms. This review summarizes genetic dissection of about 50 genetic variants affecting pigmentation, behaviour, metabolic regulation, and the pattern of locomotion. The variants are controlled by mutations in about 30 different genes, and for 10 of these our group was the first to report an association between the gene and a phenotype. Almost half of the reported mutations occur in non-coding sequences, suggesting that this is the most common type of polymorphism underlying phenotypic variation since this is a biased list where the proportion of coding mutations are inflated as they are easier to find. The review documents that structural changes (duplications, deletions, and inversions) have contributed significantly to the evolution of phenotypic diversity in domestic animals. Finally, we describe five examples of evolution of alleles, which means that alleles have evolved by the accumulation of several consecutive mutations affecting the function of the same gene.

Genome-Wide Linkage Analysis Identifies Loci for Physical Appearance Traits in Chickens

Physical appearance traits, such as feather-crested head, comb size and type, beard, wattles size, and feathered feet, are used to distinguish between breeds of chicken and also may be associated with economic traits. In this study, a genome-wide linkage analysis was used to identify candidate regions and genes for physical appearance traits and to potentially provide further knowledge of the molecular mechanisms that underlie these traits. The linkage analysis was conducted with an F2 population derived from Beijing-You chickens and a commercial broiler line. Single-nucleotide polymorphisms were analyzed using the Illumina 60K Chicken SNP Beadchip. The data were used to map quantitative trait loci and genes for six physical appearance traits. A 10-cM/0.51-Mb region (0.0−10.0 cM/0.00−0.51 Mb) with 1% genome-wide significant level on LGE22C19W28_E50C23 linkage group (LGE22) for crest trait was identified, which is likely very closely linked to the HOXC8. A QTL with 5% chromosome-wide significant level for comb weight, which partly overlaps with a region identified in a previous study, was identified at 74 cM/25.55 Mb on chicken (Gallus gallus; GG) chromosome 3 (i.e., GGA3). For beard and wattles traits, an identical region 11 cM/2.23 Mb (0.0−11.0 cM/0.00−2.23 Mb) including WNT3 and GH genes on GGA27 was identified. Two QTL with 1% genome-wide significant level for feathered feet trait, one 9-cM/2.80-Mb (48.0-57.0/13.40-16.20 Mb) region on GGA13, and another 12-cM/1.45-Mb (41.0−53.0 cM/11.37−12.82 Mb) region on GGA15 were identified. These candidate regions and genes provide important genetic information for the physical appearance traits in chicken.

Development, regeneration, and evolution of feathers

The feather is a complex ectodermal organ with hierarchical branching patterns. It provides functions in endothermy, communication, and flight. Studies of feather growth, cycling, and health are of fundamental importance to avian biology and poultry science. In addition, feathers are an excellent model for morphogenesis studies because of their accessibility, and their distinct patterns can be used to assay the roles of specific molecular pathways. Here we review the progress in aspects of development, regeneration, and evolution during the past three decades. We cover the development of feather buds in chicken embryos, regenerative cycling of feather follicle stem cells, formation of barb branching patterns, emergence of intrafeather pigmentation patterns, interplay of hormones and feather growth, and the genetic identification of several feather variants. The discovery of feathered dinosaurs redefines the relationship between feathers and birds. Inspiration from biomaterials and flight research further fuels biomimetic potential of feathers as a multidisciplinary research focal point.

A cis-regulatory mutation of PDSS2 causes silky-feather in chickens

Silky-feather has been selected and fixed in some breeds due to its unique appearance. This phenotype is caused by a single recessive gene (hookless, h). Here we map the silky-feather locus to chromosome 3 by linkage analysis and subsequently fine-map it to an 18.9 kb interval using the identical by descent (IBD) method. Further analysis reveals that a C to G transversion located upstream of the prenyl (decaprenyl) diphosphate synthase, subunit 2 (PDSS2) gene is causing silky-feather. All silky-feather birds are homozygous for the G allele. The silky-feather mutation significantly decreases the expression of PDSS2 during feather development in vivo. Consistent with the regulatory effect, the C to G transversion is shown to remarkably reduce PDSS2 promoter activity in vitro. We report a new example of feather structure variation associated with a spontaneous mutation and provide new insight into the PDSS2 function.

The feather is an excellent model for evolution and development due to its complex structure and vast diversity. Some chickens have silky-feather because of a loss of hooklets in pennaceous feathers, while most chickens have the wild-type normal feather. Hooklets are formed in the last differentiation stage of the life cycle of a pennaceous feather. Chickens with silky-feather are homozygous for a recessive allele (hookless, h). Silkie chicken from China is one of the breeds showing the fascinating silky-feather phenotype and the breed has been known for hundreds of years. In this study, we mapped the silky-feather locus to an 18.9 kb interval and identified a single nucleotide polymorphism (SNP) completely associated with silky-feather. The causative mutation is located 103 base pairs upstream of the coding sequence of prenyl (decaprenyl) diphosphate synthase, subunit 2 (PDSS2). The expression of the PDSS2 gene is decreased in silky-feather skin during feather development in vivo. The silky-feather allele also reduces the PDSS2 promoter activity in vitro. This is the first report of feather structure variation associated with PDSS2 and provides new insight into molecular signaling in the late development stage of feather morphogenesis.

Genome-wide patterns of genetic variation in two domestic chickens

Domestic chickens are excellent models for investigating the genetic basis of phenotypic diversity, as numerous phenotypic changes in physiology, morphology, and behavior in chickens have been artificially selected. Genomic study is required to study genome-wide patterns of DNA variation for dissecting the genetic basis of phenotypic traits. We sequenced the genomes of the Silkie and the Taiwanese native chicken L2 at ∼23- and 25-fold average coverage depth, respectively, using Illumina sequencing. The reads were mapped onto the chicken reference genome (including 5.1% Ns) to 92.32% genome coverage for the two breeds. Using a stringent filter, we identified ∼7.6 million single-nucleotide polymorphisms (SNPs) and 8,839 copy number variations (CNVs) in the mapped regions; 42% of the SNPs have not found in other chickens before. Among the 68,906 SNPs annotated in the chicken sequence assembly, 27,852 were nonsynonymous SNPs located in 13,537 genes. We also identified hundreds of shared and divergent structural and copy number variants in intronic and intergenic regions and in coding regions in the two breeds. Functional enrichments of identified genetic variants were discussed. Radical nsSNP-containing immunity genes were enriched in the QTL regions associated with some economic traits for both breeds. Moreover, genetic changes involved in selective sweeps were detected. From the selective sweeps identified in our two breeds, several genes associated with growth, appetite, and metabolic regulation were identified. Our study provides a framework for genetic and genomic research of domestic chickens and facilitates the domestic chicken as an avian model for genomic, biomedical, and evolutionary studies.

Genomic diversity and evolution of the head crest in the rock pigeon

The geographic origins of breeds and the genetic basis of variation within the widely distributed and phenotypically diverse domestic rock pigeon (Columba livia) remain largely unknown. We generated a rock pigeon reference genome and additional genome sequences representing domestic and feral populations. We found evidence for the origins of major breed groups in the Middle East and contributions from a racing breed to North American feral populations. We identified the gene EphB2 as a strong candidate for the derived head crest phenotype shared by numerous breeds, an important trait in mate selection in many avian species. We also found evidence that this trait evolved just once and spread throughout the species, and that the crest originates early in development by the localized molecular reversal of feather bud polarity.