Mapping QTL affecting a systemic sclerosis-like disorder in a cross between UCD-200 and red jungle fowl chickens
Highlights
► The UCD-200 chicken model for human systemic sclerosis has been analysed. ► A cross between the UCD-200 chicken and its ancestor have been used for QTLmapping. ► Three suggestive disease predisposing loci have been mapped to chromosome 2, 12 and 14. ► Several potential candidate genes are located within the identified QTL regions. ► Three of the orthologues have been suggested to be involved in human systemic sclerosis.
Introduction
Systemic sclerosis (SSc) or scleroderma is a rare autoimmune disease of the skin and internal organs such as the gastrointestinal tract, lungs, kidneys and heart. It is characterized by microvascular damage, immune dysfunction, and excessive deposition of extracellular matrix (ECM) (Chizzolini, 2007). The aetiology of SSc is poorly understood but it is generally accepted that both environmental and genetic factors contribute to the disease. Some recent genetic studies have identified association between several genes and SSc in humans, including common allelic variants in Exocyst complex component 2-Interferon regulatory factor 4 (EXOC2-IRF4), Cluster of differentiation 247 (CD247), Transforming growth factor beta receptor I (TGFBR1), Collagen alpha 2(I) chain (COL1A2) and Secreted protein acidic and rich in cystein (SPARC) (Pannu et al., 2006, Radstake et al., 2010, Zhou et al., 2003). However, not all of them could be confirmed in independent studies (Agarwal, 2010, Lagan et al., 2005). Some possible reasons for the different results might be clinical heterogeneity within patients diagnosed with SSc, small effects of single genes on SSc predisposition, and low disease incidence, meaning that effects can be missed unless very large cohorts are examined.
Genetic studies in animal models can provide a valuable complement to human studies because experimental crosses can be generated. Animal models also enable in-depth experimental validation and exploration of the molecular basis of identified genes (Andersson and Georges, 2004). One of the best animal models for SSc is the University of California at Davis-line 200 chicken (UCD-200). UCD-200 chickens develop a hereditary disease displaying all the disease characteristics of human SSc, including the typical microvascular alterations, perivascular mononuclear cell infiltration, fibrosis of skin and viscera, and autoantibody production, e.g. anti-nuclear antibodies (ANA), and anti-endothelial cell antibodies (AECA) (Beyer et al., 2010, Gershwin et al., 1981). There are clear genetic, immunological and environmental influences on disease outcome in similarity with the human condition including a difference in disease frequency between the sexes (Beyer et al., 2010, Gershwin et al., 1981, Wick et al., 2006). Chickens are ideal for genetic studies since large numbers of offspring can rapidly be produced from each pair of parents, and phenotypic characteristics are easily assessed. Another advantage of the UCD-200 chicken model of SSc compared to other animal models for SSc, is the opportunity to study the disease in the embryo, i.e. long before clinical and immunological symptoms emerge. In common with many autoimmune diseases, women tend to be more affected with SSc than men, but in crosses including the UCD-200 line, males have a higher disease incidence (Selmi et al., 2006, Wick et al., 2006). However, in both chickens and humans it is the homogametic sex that is more affected; male birds are homogametic ZZ and female birds are ZW.
One to two weeks after hatching, UCD-200 birds manifest typical comb lesions with a current incidence of 97.5% (Wick et al., 2006). Disease progression starts with erythema and oedema of the comb leading to necrosis and, in most cases, loss of the comb. These lesions are considered equivalent to fingertip ulcers in human SSc. Some of the animals also show ischemic lesions of toes or develop dermal lesions at the neck. In the inflammatory phase of the disease, T-cell receptor (TCR)γ/δ+/CD3+/MHC class II− T-cells prevail in the stratum papillare, while TCRα/β+/CD3+/CD4+/MHC class II+ T-cells predominate in the deeper dermis. The early inflammatory stage subsequently progresses to a chronic stage characterized by fibrosis with excessive accumulation of collagen types I, III, and VI. Visceral involvement occurs in the oesophagus, small intestine, lungs, and kidneys with early vascular alterations and inflammation, followed by fibrosis (Nguyen et al., 2000, Wick et al., 2006).
Earlier crosses of UCD-200 chickens with healthy controls resulted in only healthy birds in the F1 generation, suggesting a recessive autosomal mode of gene action. F2 progeny (F1 × F1) showed a low incidence (4%) of affected individuals. This suggests that multiple loci and interactions between loci may be important, as for a typical single recessive gene with full penetrance, 25% of F2 individuals are expected to be diseased. However, the number of genes involved should be limited because a high incidence of scleroderma was attained after relatively few generations of selective breeding (Wick et al., 2006). An F2 design is generally more powerful compared to a backcross (BC) design, because both F1 parents should be heterozygous at the causative loci. However, if the disorder is dependent on interactions between several loci and the incidence of disease is low in the F2, as in this case, a BC can be more powerful if it generates more affected individuals. For example, if a trait is caused by recessive alleles at four unlinked loci, in an F2 design (1/4)4 = 1/256 of the progeny would be diseased, whereas (1/2)4 = 1/16 of the progeny would be affected in a BC design. Backcrossing F1 chickens to UCD-200 chickens, resulted in approximately 50% of the chickens being affected (Abplanalp et al., 1990). Therefore, in the present study, a backcross population was constructed for analyzing SSc.
Here, we report results aimed at dissecting the genetic architecture underlying avian SSc in the UCD-200 chicken population. A genome-wide scan for individual and interacting Quantitative Trait Loci (QTL) was performed to identify novel loci involved in the disorder.
Section snippets
Animals
An F1 population was produced from eight UCD-200 (four males and four females) and eight red jungle fowl (RJF) chickens (four males and four females). A total of 22 F1 individuals (2 males and 20 females) were crossed to 12 UCD-200 chickens (4 males and 8 females) to generate 501 BC animals in 26 full-sib families. The pedigree was controlled and corrected with a script checking for inheritance errors. Blood was collected from the wing vein of all individuals and DNA was extracted prior to
Results and discussion
The total sex-averaged linkage map, incorporating 326 SNPs evenly spread over 27 of the 39 chicken chromosomes, covered 2623 cM. Marker positions in the linkage map and the base pair position from the May 2006 (v2.1) chicken genome assembly are provided in the Supplementary table.
Our map was slightly shorter than earlier chicken linkage maps that were primarily based on microsatellite data, e.g. the consensus map from 2000 (Groenen et al., 2000) and other individual populations (Jacobsson et
Conclusions
This study illustrates the usefulness of the UCD-200 chicken as a model for SSc. There was a significant difference in disease frequency between the sexes, with the homogametic males being more affected. In humans, females, which are also the homogametic sex, are more affected and understanding the reasons for this is an interesting subject for further study. Interestingly, we observed less disease in females with a W chromosome inherited from the UCD-200 founder line. This indicates a possible
Acknowledgement
We thank Ulla Gustafson for excellent technical support. We are gratful to Ronald Nelson for his help to prepare Fig. 1, Fig. 2. This project were supported by the Swedish Foundation for Strategic Research, EURYI, the Austrian Research Fund (FWF-project P18726-B05), the Swedish Research Council (contracts 80576801, 80409601 and 70374401) and Region Västra Götaland (ALFGBG-771712). The SNP&SEQ Technology Platform (www.genotyping.se), is supported by Uppsala University, Uppsala University
References (44)
- et al.
Transforming growth factor-beta in human platelets. Identification of a major storage site, purification, and characterization
Journal of Biological Chemistry
(1983) - et al.
Guidelines for genotyping in genomewide linkage studies: single-nucleotide-polymorphism maps versus microsatellite maps
American Journal of Human Genetics
(2004) - et al.
Association of functional microsatellites in the human type I collagen alpha2 chain (COL1A2) gene with systemic sclerosis
Biochemical and Biophysical Research Communications
(2000) - et al.
Assignment of fourteen microsatellite markers to the chicken linkage map
Poultry Science
(2004) - et al.
The role of TGF-beta in growth, differentiation, and maturation of B lymphocytes
Microbes and Infection
(1999) - et al.
Endothelial injury in internal organs of University of California at Davis line 200 (UCD 200) chickens, an animal model for systemic sclerosis (Scleroderma)
Journal of Autoimmunity
(2000) - et al.
Insulin-like growth factor binding proteins 3 and 5 are overexpressed in idiopathic pulmonary fibrosis and contribute to extracellular matrix deposition
American Journal of Pathology
(2005) - et al.
Avian models with spontaneous autoimmune diseases
Advances in Immunology
(2006) - et al.
Genetic control of avian scleroderma
Immunogenetics
(1990) The genetics of systemic sclerosis
Discovery Medicine
(2010)
Domestic-animal genomics: deciphering the genetics of complex traits
Nature Reviews Genetics
Impaired Smad7-Smurf-mediated negative regulation of TGF-beta signaling in scleroderma fibroblasts
Journal of Clinical Investigation
Altered procollagen mRNA expression during the progression of avian scleroderma
Molecular Medicine
A genetic algorithm based method for stringent haplotyping of family data
BMC Genetics
Animal models of systemic sclerosis: prospects and limitations
Arthritis and Rheumatism
R/qtl: QTL mapping in experimental crosses
Bioinformatics
Recruitment and activation of macrophages by pathogenic CD4 T cells in type 1 diabetes: evidence for involvement of CCR8 and CCL1
Journal of immunology
Update on pathophysiology of scleroderma with special reference to immunoinflammatory events
Annals of Medicine
Empirical threshold values for quantitative trait mapping
Genet
An improved method for estimating chromosomal line origin in QTL analysis of crosses between outbred lines
G3
Hypoxia-induced increase in the production of extracellular matrix proteins in systemic sclerosis
Arthritis and Rheumatism
Highly parallel SNP genotyping
Cold Spring Harbor Symposia on Quantitative Biology
Cited by (6)
Autoimmune diseases of poultry
2021, Avian ImmunologyAutoimmune Diseases of Poultry
2013, Avian Immunology: Second EditionNonendocrine mechanisms of sex bias in rheumatic diseases
2019, Nature Reviews RheumatologyAnimal models of systemic sclerosis
2015, Current Pharmaceutical DesignAnimal models of systemic sclerosis: Their utility and limitations
2014, Open Access Rheumatology: Research and ReviewsMAPfastR: Quantitative trait loci mapping in outbred line crosses
2013, G3: Genes, Genomes, Genetics
- 1
The authors have contributed equally to this manuscript.