RESUMO
The products of the Legionella pneumophila dot/icm genes enable the bacterium to replicate within a macrophage vacuole. This study demonstrates that the Dot/Icm machinery promotes macropinocytotic uptake of L. pneumophila into mouse macrophages. In mouse strains harboring a permissive Lgn1 allele, L. pneumophila promoted formation of vacuoles that were morphologically similar to macropinosomes and dependent on the presence of an intact Dot/Icm system. Macropinosome formation appeared to occur during, rather than after, the closure of the plasma membrane about the bacterium, since a fluid-phase marker preloaded into the macrophage endocytic path failed to label the bacterium-laden macropinosome. The resulting macropinosomes were rich in GM1 gangliosides and glycosylphosphatidylinositol-linked proteins. The Lgn1 allele restrictive for L. pneumophila intracellular replication prevented dot/icm-dependent macropinocytosis, with the result that phagosomes bearing the microorganism were targeted into the endocytic network. Analysis of macrophages from recombinant inbred mouse strains support the model that macropinocytotic uptake is controlled by the Lgn1 locus. These results indicate that the products of the dot/icm genes and Lgn1 are involved in controlling an internalization route initiated at the time of bacterial contact with the plasma membrane.
Assuntos
Genes Bacterianos/fisiologia , Legionella pneumophila/imunologia , Macrófagos/imunologia , Pinocitose/imunologia , Animais , Células da Medula Óssea/citologia , Células da Medula Óssea/imunologia , Membrana Celular/microbiologia , Membrana Celular/fisiologia , Células Cultivadas , Feminino , Macrófagos/citologia , Macrófagos/microbiologia , Camundongos , Camundongos Endogâmicos A , Camundongos Endogâmicos C57BLRESUMO
Prior genetic and physical mapping has shown that the Naip gene cluster on mouse chromosome 13D1-D3 contains a gene, Lgn1, that is responsible for determining the permissivity of ex vivo macrophages to Legionella pneumophila replication. We have identified differences in the structure of the Naip array among commonly used inbred mouse strains, although these gross structural differences do not correlate with differences in L. pneumophila permissiveness. A physical map of the region employing clones of the C57BL/6J haplotype confirms that there are fewer copies of Naip in this strain than are in the physical map of the 129 haplotype. We have also refined the genetic location of Lgn1, leaving only Naip2 and Naip5 as candidates for Lgn1. Our genetic map suggests the presence of two hotspots of recombination within the Naip array, indicating that the 3' portion of Naip may be involved in the genomic instability at this locus.
Assuntos
Apoptose/genética , Legionella pneumophila/genética , Legionella pneumophila/patogenicidade , Doença dos Legionários/genética , Proteínas do Tecido Nervoso/genética , Mapeamento Físico do Cromossomo/métodos , Animais , Linhagem Celular , Predisposição Genética para Doença/genética , Doença dos Legionários/etiologia , Camundongos , Camundongos Endogâmicos A , Camundongos Endogâmicos C57BL , Dados de Sequência Molecular , Família Multigênica/genética , Proteína Inibidora de Apoptose NeuronalRESUMO
A mouse locus called Lgn1 determines differences in macrophage permissiveness for the intracellular replication of Legionella pneumophila. The only regional candidate genes for this phenotype difference lie within a cluster of closely linked paralogs of the Neuronal Apoptosis Inhibitory Protein (Naip) gene. Previous genetic and physical mapping of the Lgn1 phenotype narrowed it to an interval containing only Naip2 and Naip5, suggesting that there is not complete functional overlap among the mouse Naip loci. In order to gather more information about polymorphisms among the Naip genes of the 129 mouse haplotype, we have determined the genomic sequence of a substantial portion of the 129 Naip gene array. We have constructed an evolutionary model for the expansion of the Naip gene array from a single progenitor Naip gene. This model predicts the presence of two distinct families of Naip paralogs: Naip1/2/3 and Naip4/5/6/7. Unlike the divergences among all the other Naip paralogs, the splits among Naip4, Naip5, Naip6, and Naip7 occurred relatively recently. The high degree of sequence conservation within the Naip4/5/6/7 family increases the likelihood of functional overlap among these genes.
Assuntos
Apoptose/genética , Genoma , Família Multigênica , Proteínas do Tecido Nervoso/genética , Animais , Marcadores Genéticos , Humanos , Camundongos , Dados de Sequência Molecular , Proteína Inibidora de Apoptose Neuronal , Alinhamento de Sequência , Análise de Sequência de DNARESUMO
The orthologous genomic segments on mouse chromosome 13D1-D3 and human chromosome 5q11.2-q13.3 have been extensively studied because of their involvement in two distinct disease phenotypes, spinal muscular atrophy (SMA) in human and susceptibility to Legionella pneumophila (determined by Lgn1) in mice. The overlapping intervals in both species contain genomic amplifications of distinct structure, indicating an independent origin. We have endeavored to construct a comprehensive comparative gene map of the mouse and human Lgn1/SMA intervals in the hopes that the origins and maintenance of the genomic amplifications may become clear. Our comparative gene map demonstrates that the only regional gene in common between the amplified segments in mouse and human is the Lgn1 candidate Naip/NAIP. We have also determined that mice of the 129 haplotype harbor seven intact and three partial Naip transcription units arranged in a closely linked direct repeat on chromosome 13. Several, but not all, of these Naip loci are contained within the Lgn1 critical interval. We present a model for the origins of the mouse and human repetitive arrays from a common ancestral haplotype.
