Re-evaluation of Chicken CXCR1 Determines the True Gene Structure

Abstract

The original report of chicken CXCR1 (Li, Q. J., Lu, S., Ye, R. D., and Martins-Green, M. (2000) Gene (Amst.) 257, 307-317) described it as a single exon gene, with two isoforms (differing in their start codon). In comparison with mammalian CXCR1, the reported chicken CXCR1 was longer at both the NH 2 and COOH termini, and it lacked the conserved (C/S)CXNP motif present in the last transmembrane region of all known chemokine receptors. A re-evaluation of chicken CXCR1, comparing known expressed sequence tags with the chicken genome sequence, suggested that the gene contains two exons. We isolated a cDNA corresponding to our prediction, which was significantly different in sequence to the reported CXCR1. In particular, there were three frameshifts in our sequence, compared with the reported sequence, that restored higher identity in the COOH-terminal half of the protein to mammalian CXCR1 (61% total amino acid identity compared with 52% for the reported CXCR1), restored the (C/S)CXNP motif, and gave a predicted protein of the same length as mammalian CXCR1. In human, CXCR1 is the receptor for CXCL8. In the chicken, there are two syntenic genes, CXCLi1 and CXCLi2, which look equally like orthologues of human CXCL8. We demonstrate that both of these chemokines are ligands for chicken CXCR1. We also demonstrate that heterophils express chicken CXCR1 and that the receptor is G␣ i protein-linked.CXC chemokines can be classified according to the presence of the tripeptide motif glutamic acid-leucine-arginine (ELR) in the NH 2 -terminal region before the first conserved cysteine. In mammals, ELR ϩ chemokines are specific for polymorphonuclear leukocytes (2), whereas ELR Ϫ chemokines attract a variety of leukocytes (3, 4). In mammals, ELR ϩ CXC chemokines bind to two receptors, CXCR1 and CXCR2, with different affinities. Both receptors are the principal expressed chemokine receptors on neutrophils.To understand the evolution of the chemokines and their receptors in concert with the evolution of different developmental and responsive modes of the immune system, the recently released chicken genome sequence (5) was used to catalogue a complete list of chicken chemokines and their receptors (6 -8). All four classes of chemokines were identified in the chicken genome, although the total number, 24, was fewer than identified in human (42) or mouse (35). For the homeostatic chemokines present, a clear orthologous relationship could be identified, suggesting conservation of function (8). However, for the inflammatory chemokines, the relationships between the chicken chemokines and their mammalian homologues remain unclear (8). All four classes of chemokine receptors were also identified in the chicken genome (8), again with a smaller total repertoire (13 genes) in the chicken as compared with mammals. Similarly to the chemokines, the homeostatic chemokine receptors had obvious mammalian orthologues, whereas the relationships between the inflammatory chemokine receptors remain unclear.In the absence of clear orthologous relation...

Strong inflammatory responses and apoptosis in the oviducts of egg-laying hens caused by genotype VIId Newcastle disease virus

“…The highest levels of expression of the examined genes corresponded with the significant clinical signs and the inflammatory responses in the oviductal tissues. In the chicken, there are two syntenic genes (CXCLi1 and CXCLi2) that mainly chemoattract heterophils and monocytes, respectively [27]. Interestingly, although both the CXCL chemokines were upregulated following NDV infection in this study, the CXCLi2 mRNA expression levels were higher compared to CXCLi1.…”

The effects of different velogenic NDV infections on the chicken bursa of Fabricius

“…4) but with lower viral load (Table 2) in the chicken bursa than in the case of NDV IBS002 infection. Chicken CXCLi2, a proinflammatory chemokine, is expressed by and is chemotactic for monocytes [39]. On the other hand, IL-18 is a pro-inflammatory cytokine secreted by various immune and none-immune cells including monocytes, macrophages and lymphocytes that promotes expression of IFN-γ by T cells [40], which subsequently activates macrophages to produce NO [41, 42].…”

Analysis of immune responses induced by avian pathogenic Escherichia coli infection in turkeys and their association with resistance to homologous re-challenge

“…TaqMan real-time quantitative reverse transcriptase polymerase chain reaction (qRT-PCR) was used to quantify mRNA levels of a proinflammatory cytokine (IL-1β), a proinflammatory chemokine (CXCLi2), a Th1 signature cytokine (interferon (IFN)-γ), a Th2 signature cytokine (interleukin (IL)-13) and two T regulatory cytokines (IL-10 and TGF-β4), with 28S rRNA as a housekeeping gene, essentially as described [26,27]. Primers and probes specific for turkey mRNAs are given in Table  1.…”

“…The passive reference dye 6-carboxy-c-rhodamine, not involved in amplification, was used for normalisation of the reporter signal. Data are expressed in terms of the cycle threshold value (Ct), normalised for each sample using the Ct value of 28S rRNA product for the same sample, as described previously [26,27]. Final results are shown as corrected ΔCt, using the normalised value.…”