ABSTRACT
Chemokines and their receptors are important in cell migration during inflammation, in the establishment of functional lymphoid microenvironments, and in organogenesis. The chemokine receptor CXCR4 is broadly expressed in cells of both the immune and the central nervous systems and can mediate migration of resting leukocytes and haematopoietic progenitors in response to its ligand, SDF-1. CXCR4 is also a major receptor for strains of human immunodeficiency virus-1 (HIV-1) that arise during progression to immunodeficiency and AIDS dementia. Here we show that mice lacking CXCR4 exhibit haematopoietic and cardiac defects identical to those of SDF-1-deficient mice, indicating that CXCR4 may be the only receptor for SDF-1. Furthermore, fetal cerebellar development in mutant animals is markedly different from that in wild-type animals, with many proliferating granule cells invading the cerebellar anlage. This is, to our knowledge, the first demonstration of the involvement of a G-protein-coupled chemokine receptor in neuronal cell migration and patterning in the central nervous system. These results may be important for designing strategies to block HIV entry into cells and for understanding mechanisms of pathogenesis in AIDS dementia.
Subject(s)
Antigens, CD , Cerebellum/embryology , Hematopoiesis/physiology , Receptors, CXCR4/physiology , Animals , B-Lymphocytes/cytology , Chemokine CXCL12 , Chemokines, CXC/physiology , Chemotaxis , Embryonic and Fetal Development/physiology , Fetal Death , Heart Septal Defects/etiology , Leukocyte Common Antigens/biosynthesis , Leukosialin , Liver/cytology , Liver/embryology , Mice , Mutation , Neurons/physiology , RNA, Messenger/metabolism , Receptors, CXCR4/deficiency , Receptors, CXCR4/genetics , Sialoglycoproteins/biosynthesis , Signal Transduction , T-Lymphocytes/cytologyABSTRACT
The joining of immunoglobulin gene segments during B cell development consists of a tightly regulated series of rearrangement steps. A variety of experiments have suggested that transcription is involved in activating the locus as substrate for the V(D)J recombinase. Here, we have characterized a region located immediately upstream of the most J-proximal D element (DQ52), which contains both promoter and enhancer activities preferentially active in precursors of B cells. Interestingly, this DQ52 regulatory element is inevitably deleted in fully rearranged H chain genes. We propose that it is involved in the early activation and rearrangement events at the IgH locus.
Subject(s)
Enhancer Elements, Genetic , Genes, Immunoglobulin , Immunoglobulin Heavy Chains/genetics , Promoter Regions, Genetic , Animals , Base Sequence , Cell Line , Chromosome Mapping , Gene Rearrangement , Mice , Molecular Sequence DataABSTRACT
The expression of immunoglobulin (Ig) genes is regulated at two levels: rearrangement of individual gene segments and transcription of continuous genes. To find transacting factors involved in mediating locus- and segment specific gene activation and expression, we surveyed a 3600-bp genomic region of the murine Ig heavy chain locus, spanning from the DQ52 element to the Ig heavy chain intron enhancer. We discovered nine, previously undescribed, protein-DNA complexes and estimated their individual binding-affinity preferences (Kr) by quantitative gel shift measurements. We observed one novel protein DNA interaction at the enhancer, two in the JH1 region and six within a 300-bp region immediately 5' to the DQ52 locus. The latter show a complex and specific binding pattern when comparing nuclear extracts derived from pre-B cells and fibroblasts. Further characterization of the interactions at the DQ52 locus by electron microscopy revealed the preferential formation of a protein complex binding to the DQ52 locus with pre B cell extracts. This behavior and the clustering of interaction sites 5' to the DQ52 element suggest that this region is involved in the regulation of heavy chain gene assembly.
Subject(s)
Chromosome Mapping , DNA/metabolism , Genes, Immunoglobulin , Immunoglobulin Heavy Chains/genetics , Proteins/metabolism , Animals , Base Sequence , Binding Sites , Enhancer Elements, Genetic , Mice , Microscopy, Electron , Molecular Sequence DataABSTRACT
An HLA-B44 cDNA clone was identified in a cDNA library constructed from an HLA-B44 homozygous cell line. The DNA sequence was determined and was found to contain the complete coding sequence but for (probably) the three N-terminal codons. Comparisons of the derived amino acid sequence with other HLA-A and -B locus amino acid sequences revealed four HLA-B44-specific substitutions including a new polymorphic site. Regions of strong sequence conservation for HLA-B-locus products were found at the nucleotide and amino acid levels.
