ABSTRACT
STRL33/BONZO/TYMSTR is an orphan chemokine and HIV/SIV coreceptor receptor that is expressed on activated T lymphocytes. We describe an expression cloning strategy whereby we isolated a novel chemokine, which we name CXCL16. CXCL16 is an alpha (CXC) chemokine but also has characteristics of CC chemokines and a structure similar to fractalkine (neurotactin) in having a transmembrane region and a chemokine domain suspended by a mucin-like stalk. A recombinant version of CXCL16 fails to mediate chemotaxis to all known chemokine receptor transfectants tested but does mediate robust chemotaxis, high affinity binding, and calcium mobilization to Bonzo receptor transfectants, indicating that this is a unique receptor ligand interaction. In vitro polarized T cell subsets including Th1, Th2, and Tr1 cells express functional Bonzo, suggesting expression of this receptor in chronic inflammation, which we further verified by demonstration of CXCL16-mediated migration of tonsil-derived CD4(+) T lymphocytes. CXCL16 is expressed on the surface of APCs including subsets of CD19(+) B cells and CD14(+) monocyte/macrophages, and functional CXCL16 is also shed from macrophages. The combination of unique structural features of both Bonzo and CXCL16 suggest that this interaction may represent a new class of ligands for this receptor family. Additionally, this chemokine might play a unique dual role of attracting activated lymphocyte subsets during inflammation as well as facilitating immune responses via cell-cell contact.
Subject(s)
Chemokines, CC/chemistry , Chemokines, CX3C/chemistry , Chemokines, CXC/chemistry , Chemokines, CXC/genetics , Cloning, Molecular/methods , Membrane Proteins/chemistry , Membrane Proteins/genetics , Receptors, Cytokine/metabolism , Receptors, G-Protein-Coupled , Receptors, Immunologic , Receptors, Virus , Amino Acid Sequence , Blotting, Southern , Cell Line , Cell Membrane/genetics , Cell Membrane/immunology , Cell Membrane/metabolism , Chemokine CXCL16 , Chemokines, CXC/biosynthesis , Chemokines, CXC/physiology , DNA, Complementary/isolation & purification , Glycosylation , Humans , Leukocytes/immunology , Leukocytes/metabolism , Ligands , Lymphocyte Activation , Macrophages/immunology , Macrophages/metabolism , Membrane Proteins/biosynthesis , Membrane Proteins/physiology , Molecular Sequence Data , RNA/biosynthesis , Receptors, CXCR6 , Receptors, Chemokine , Receptors, Scavenger , Recombinant Fusion Proteins/metabolism , Sequence Analysis, Protein , T-Lymphocyte Subsets/immunology , T-Lymphocyte Subsets/metabolism , TransfectionABSTRACT
The normal development of shoot structures depends on controlling the growth, proliferation and differentiation of cells derived from the shoot apical meristem. We have identified the CYP78A5 gene encoding a putative cytochrome P450 monooxygenase that is the first member of the CYP78 family from Arabidopsis. This gene is strongly expressed in the peripheral regions of the vegetative and reproductive shoot apical meristems, defining a boundary between the central meristematic zone and the developing organ primordia. In addition, CYP78A5 shows a dynamic pattern of expression during floral development. Overexpression of CYP78A5 affects multiple cell types, causing twisting and kinking of the stem and defects in floral development. To define the relationship of CYP78A5 to genes controlling meristem function, we examined CYP78A5 expression in plants mutant for SHOOT MERISTEMLESS, ZWILLE and ARGONAUTE, and have found that CYP78A5 expression is altered in these mutant backgrounds. We propose that CYP78A5 has a role in regulating directional growth in the peripheral region of the shoot apical meristem in response to cues established by genes regulating meristem function.
Subject(s)
Arabidopsis/growth & development , Arabidopsis/genetics , Cytochrome P-450 Enzyme System/genetics , Genes, Plant , Amino Acid Sequence , Arabidopsis/cytology , Base Sequence , Cloning, Molecular , DNA, Plant/genetics , Gene Expression Regulation, Developmental , Gene Expression Regulation, Plant , In Situ Hybridization , Meristem/cytology , Meristem/growth & development , Microscopy, Electron, Scanning , Molecular Sequence Data , Mutation , Phenotype , Plants, Genetically ModifiedABSTRACT
The APETALA3 floral homeotic gene is required for petal and stamen development in Arabidopsis. APETALA3 transcripts are first detected in a meristematic region that will give rise to the petal and stamen primordia, and expression is maintained in this region during subsequent development of these organs. To dissect how the APETALA3 gene is expressed in this spatially and temporally restricted domain, various APETALA3 promoter fragments were fused to the uidA reporter gene encoding beta-glucuronidase and assayed for the resulting patterns of expression in transgenic Arabidopsis plants. Based on these promoter analyses, we defined cis-acting elements required for distinct phases of APETALA3 expression, as well as for petal-specific and stamen-specific expression. By crossing the petal-specific construct into different mutant backgrounds, we have shown that several floral genes, including APETALA3, PISTILLATA, UNUSUAL FLORAL ORGANS, and APETALA1, encode trans-acting factors required for second-whorl-specific APETALA3 expression. We have also shown that the products of the APETALA1, APETALA3, PISTILLATA and AGAMOUS genes bind to several conserved sequence motifs within the APETALA3 promoter. We present a model whereby spatially and temporally restricted APETALA3 transcription is controlled via interactions between proteins binding to different domains of the APETALA3 promoter.
