Rima Zoorob

The chicken B locus is a minimal essential major histocompatibility complex.

Here we report the sequence of the region that determines rapid allograft rejection in chickens, the chicken major histocompatibility complex (MHC). This 92-kilobase region of the B locus contains only 19 genes, making the chicken MHC roughly 20-fold smaller than the human MHC. Virtually all the genes have counterparts in the human MHC, defining a minimal essential set of MHC genes conserved over 200 million years of divergence between birds and mammals. They are organized differently, with the class III region genes located outside the class II and class I region genes. The absence of proteasome genes is unexpected and might explain unusual peptide-binding specificities of chicken class I molecules. The presence of putative natural killer receptor gene(s) is unprecedented and might explain the importance of the B locus in the response to the herpes virus responsible for Mareks disease. The small size and simplicity of the chicken MHC allows co-evolution of genes as haplotypes over considerable periods of time, and makes it possible to study the striking MHC-determined pathogen-specific disease resistance at the molecular level.

Cloning and Characterization of Chicken IL-10 and Its Role in the Immune Response to Eimeria maxima

We isolated the full-length chicken IL-10 (chIL-10) cDNA from an expressed sequence tag library derived from RNA from cecal tonsils of Eimeria tenella-infected chickens. It encodes a 178-aa polypeptide, with a predicted 162-aa mature peptide. Chicken IL-10 has 45 and 42% aa identity with human and murine IL-10, respectively. The structures of the chIL-10 gene and its promoter were determined by direct sequencing of a bacterial artificial chromosome containing chIL-10. The chIL-10 gene structure is similar to (five exons, four introns), but more compact than, that of its mammalian orthologues. The promoter is more similar to that of Fugu IL-10 than human IL-10. Chicken IL-10 mRNA expression was identified mainly in the bursa of Fabricius and cecal tonsils, with low levels of expression also seen in thymus, liver, and lung. Expression was also detected in PHA-activated thymocytes and LPS-stimulated monocyte-derived macrophages, with high expression in an LPS-stimulated macrophage cell line. Recombinant chIL-10 was produced and bioactivity demonstrated through IL-10-induced inhibition of IFN-γ synthesis by mitogen-activated lymphocytes. We measured the expression of mRNA for chIL-10 and other signature cytokines in gut and spleen of resistant (line C.B12) and susceptible (line 15I) chickens during the course of an E. maxima infection. Susceptible chickens showed higher levels of chIL-10 mRNA expression in the spleen, both constitutively and after infection, and in the small intestine after infection than did resistant chickens. These data indicate a potential role for chIL-10 in changing the Th bias during infection with an intracellular protozoan, thereby contributing to susceptibility of line 15I chickens.

2004 nomenclature for the chicken major histocompatibility (B and Y) complex

The first standard nomenclature for the chicken (Gallus gallus) major histocompatibility (B) complex published in 1982 describing chicken major histocompatibility complex (MHC) variability is being revised to include subsequent findings. Considerable progress has been made in identifying the genes that define this polymorphic region. Allelic sequences for MHC genes are accumulating at an increasing rate without a standard system of nomenclature in place. The recommendations presented here were derived in workshops held during International Society of Animal Genetics and Avian Immunology Research Group meetings. A nomenclature for B and Y (Rfp-Y) loci and alleles has been developed that can be applied to existing and newly defined haplotypes including recombinants. A list of the current standard B haplotypes is provided with reference stock, allele designations, and GenBank numbers for corresponding MHC class I and class IIβ sequences. An updated list of proposed names for B recombinant haplotypes is included, as well as a list of over 17 Y haplotypes designated to date.

At Least One Class I Gene in Restriction Fragment Pattern-Y (Rfp-Y), the Second MHC Gene Cluster in the Chicken, Is Transcribed, Polymorphic, and Shows Divergent Specialization in Antigen Binding Region

MHC genes in the chicken are arranged into two genetically independent clusters located on the same chromosome. These are the classical B system and restriction fragment pattern-Y (Rfp-Y), a second cluster of MHC genes identified recently through DNA hybridization. Because small numbers of MHC class I and class II genes are present in both B and Rfp-Y, the two clusters might be the result of duplication of an entire chromosomal segment. We subcloned, sequenced, and analyzed the expression of two class I loci mapping to Rfp-Y to determine whether Rfp-Y should be considered either as a second, classical MHC or as a region containing specialized MHC-like genes, such as class Ib genes. The Rfp-Y genes are highly similar to each other (93%) and to classical class Ia genes (73% with chicken B class I; 49% with HLA-A). One locus is disrupted and unexpressed. The other, YFV, is widely transcribed and polymorphic. Mature YFV protein associated with β2m arrives on the surface of chicken B (RP9) lymphoma cells expressing YFV as an epitope-tagged transgene. Substitutions in the YFV Ag-binding region (ABR) occur at four of the eight highly conserved residues that are essential for binding of peptide-Ag in the class Ia molecules. Therefore, it is unlikely that Ag is bound in the YFV ABR in the manner typical of class Ia molecules. This ABR specialization indicates that even though YFV is polymorphic and widely transcribed, it is, in fact, a class Ib gene, and Rfp-Y is a region containing MHC genes of specialized function.

Diversifying selection on MHC class I in the house sparrow (Passer domesticus)

Genes of the major histocompatibility complex (MHC) are the most polymorphic loci known in vertebrates. Two main hypotheses have been put forward to explain the maintenance of MHC diversity: pathogen‐mediated selection and MHC‐based mate choice. Host–parasite interactions can maintain MHC diversity via frequency‐dependent selection, heterozygote advantage, and diversifying selection (spatially and/or temporally heterogeneous selection). In this study, we wished to investigate the nature of selection acting on the MHC class I across spatially structured populations of house sparrows (Passer domesticus) in France. To infer the nature of the selection, we compared patterns of population differentiation based on two types of molecular markers: MHC class I and microsatellites. This allowed us to test whether the observed differentiation at MHC genes merely reflects demographic and/or stochastic processes. At the global scale, diversifying selection seems to be the main factor maintaining MHC diversity in the house sparrow. We found that (i) overall population differentiation at MHC was stronger than for microsatellites, (ii) MHC marker showed significant isolation by distance. In addition, the slope of the regression of FST on geographical distance was significantly steeper for MHC than for microsatellites due to a stronger pairwise differentiation between populations located at large geographical distances. These results are in agreement with the hypothesis that spatially heterogeneous selective pressures maintain different MHC alleles at local scales, possibly resulting in local adaptation.

Plasmodium relictum infection and MHC diversity in the house sparrow (Passer domesticus)

Antagonistic coevolution between hosts and parasites has been proposed as a mechanism maintaining genetic diversity in both host and parasite populations. In particular, the high level of genetic diversity usually observed at the major histocompatibility complex (MHC) is generally thought to be maintained by parasite-driven selection. Among the possible ways through which parasites can maintain MHC diversity, diversifying selection has received relatively less attention. This hypothesis is based on the idea that parasites exert spatially variable selection pressures because of heterogeneity in parasite genetic structure, abundance or virulence. Variable selection pressures should select for different host allelic lineages resulting in population-specific associations between MHC alleles and risk of infection. In this study, we took advantage of a large survey of avian malaria in 13 populations of the house sparrow (Passer domesticus) to test this hypothesis. We found that (i) several MHC alleles were either associated with increased or decreased risk to be infected with Plasmodium relictum, (ii) the effects were population specific, and (iii) some alleles had antagonistic effects across populations. Overall, these results support the hypothesis that diversifying selection in space can maintain MHC variation and suggest a pattern of local adaptation where MHC alleles are selected at the local host population level.

Mapping of the genetically independent chicken major histocompatibility complexes B@ and RFP-Y@ to the same microchromosome by two-color fluorescent in situ hybridization

The chicken MHC is organized in two genetically independent gene complexes B@ and RFP-Y@. Previous studies have shown the localization of the B@ complex on a small microchromosome. By using two-color fluorescent in situ hybridization, we demonstrate the localization of the RFP-Y@ complex to the same chromosome. A recombination hot spot between the two loci might account for their independent segregation.

Neuropeptide Y-family receptors Y6 and Y7 in chicken: Cloning, pharmacological characterization, tissue distribution and conserved synteny with human chromosome region

The peptides of the neuropeptide Y (NPY) family exert their functions, including regulation of appetite and circadian rhythm, by binding to G‐protein coupled receptors. Mammals have five subtypes, named Y1, Y2, Y4, Y5 and Y6, and recently Y7 has been discovered in fish and amphibians. In chicken we have previously characterized the first four subtypes and here we describe Y6 and Y7. The genes for Y6 and Y7 are located 1 megabase apart on chromosome 13, which displays conserved synteny with human chromosome 5 that harbours the Y6 gene. The porcine PYY radioligand bound the chicken Y6 receptor with a Kd of 0.80 ± 0.36 nm. No functional coupling was demonstrated. The Y6 mRNA is expressed in hypothalamus, gastrointestinal tract and adipose tissue. Porcine PYY bound chicken Y7 with a Kd of 0.14 ± 0.01 nm (mean ± SEM), whereas chicken PYY surprisingly had a much lower affinity, with a Ki of 41 nm, perhaps as a result of its additional amino acid at the N terminus. Truncated peptide fragments had greatly reduced affinity for Y7, in agreement with its closest relative, Y2, in chicken and fish, but in contrast to Y2 in mammals. This suggests that in mammals Y2 has only recently acquired the ability to bind truncated PYY. Chicken Y7 has a much more restricted tissue distribution than other subtypes and was only detected in adrenal gland. Y7 seems to have been lost in mammals. The physiological roles of Y6 and Y7 remain to be identified, but our phylogenetic and chromosomal analyses support the ancient origin of these Y receptor genes by chromosome duplications in an early (pregnathostome) vertebrate ancestor.

Pharmacological characterization of cloned chicken neuropeptide Y receptors Y1 and Y5

The neuropeptide Y (NPY) receptor subtypes Y1 and Y5 are involved in the regulation of feeding and several other physiological functions in mammals. To increase our understanding of the origin and mechanisms of the complex NPY system, we report here the cloning and pharmacological characterization of receptors Y1 and Y5 in the first non‐mammal, chicken (Gallus gallus). The receptors display 80–83% and 64–72% amino acid sequence identity, respectively, with their mammalian orthologues. The three endogenous ligands NPY, peptide YY (PYY) and pancreatic polypeptide (PP) have similar affinities as in mammals, i.e. NPY and PYY have subnanomolar affinity for both receptors whereas chicken PP bound with nanomolar affinity to Y5 but not to Y1. A notable difference to mammalian receptor subtypes is that the Y1 antagonist SR120819A does not bind chicken Y1, whereas BIBP3226 does. The Y5 antagonist CGP71863A binds to the chicken Y5 receptor. Anatomically, both Y1 and Y5 have high mRNA expression levels in the infundibular nucleus which is the homologous structure of the hypothalamic arcuate nucleus in mammals. These results suggest that some of the selective Y1 and Y5 antagonists developed in mammals can be used to study appetite regulation in chicken.

Transcriptional profiling reveals a possible role for the timing of the inflammatory response in determining susceptibility to a viral infection.

ABSTRACT Using a novel cDNA microarray prepared from sources of actively responding immune system cells, we have investigated the changes in gene expression in the target tissue during the early stages of infection of neonatal chickens with infectious bursal disease virus. Infections of two lines of chickens previously documented as genetically resistant and sensitive to infection were compared in order to ascertain early differences in the response to infection that might provide clues to the mechanism of differential genetic resistance. In addition to major changes that could be explained by previously described changes in infected tissue, some differences in gene expression on infection, and differences between the two chicken lines, were observed that led to a model for resistance in which a more rapid inflammatory response and more-extensive p53-related induction of apoptosis in the target B cells might limit viral replication and consequent pathology. Ironically, the effect in the asymptomatic neonatal infection is that more-severe B-cell depletion is seen in the more genetically resistant chicken. Changes of expression of many chicken genes of unknown function, indicating possible roles in the response to infection, may aid in the functional annotation of these genes.