Mouse cartilage matrix deficiency (cmd) caused by a 7 bp deletion in the aggrecan gene

Mouse cartilage matrix deficiency (cmd) is an autosomal recessive mutation characterized by cleft palate, short limbs, tail and snout. Heterozygous mice show normal size and phenotype, while homozygous mice die just after birth due to respiratory failure. Biochemical and immunohistochemical characterization of cmd cartilage reveals normal levels of type II collagen and link protein, but an absence of the large cartilage proteoglycan, aggrecan. Here, we have mapped the aggrecan gene to a region of mouse chromosome 7 near the cmd locus. DNA sequencing of the aggrecan gene identified a 7 bp deletion in exon 5 resulting in a severely truncated molecule. The finding of an aggrecan mutation in the cmd mouse confirms the critical role of aggrecan in cartilage formation.

Utilization of similar mechanisms by Legionella pneumophila to parasitize two evolutionarily distant host cells, mammalian macrophages and protozoa

The Legionnaires' disease bacterium, Legionella pneumophila, is an intracellular pathogen of humans that is amplified in the environment by intracellular multiplication within protozoa. Within both evolutionarily distant hosts, the bacterium multiplies in a rough endoplasmic reticulum-surrounded phagosome that is retarded from maturation through the endosomal-lysosomal degradation pathway. To gain an understanding of the mechanisms utilized by L. pneumophila to invade and replicate within two evolutionarily distant hosts, we isolated a collection of 89 mini-Tn10::kan insertion mutants that exhibited defects in cytotoxicity, intracellular survival, and replication within both U937 macrophage-like cells and Acanthamoeba polyphaga. Interestingly, the patterns of defects in intracellular survival and replication of the mutants within both host cells were highly similar, and thus we designated the defective loci in these mutants pmi (for protozoan and macrophage infectivity loci). On the basis of their ability to attach to host cells and their growth kinetics during the intracellular infection, the mutants were grouped into five groups. Groups 1 and 2 included 41 mutants that were severely defective in intracellular survival and were completely or substantially killed during the first 4 h of infection in both host cells. Three members of group 1 were severely defective in attachment to both U937 cells and A. polyphaga, and another four mutants of group 1 exhibited severe defects in attachment to A. polyphaga but only a mild reduction in their attachment to U937 cells. Four members of groups 1 and 2 were serum sensitive. Intracellular replication of mutants of the other three groups was less defective than that of mutants of groups 1 and 2, and their growth kinetics within both host cells were similar. The mutants were tested for several other phenotypes in vitro, revealing that 14 of the pmi mutants were resistant to NaCl, 3 had insertions in dot or icm, 3 were aflagellar, 12 were highly intolerant to a hyperosmotic medium, and one failed to grow in a minimal medium. Our data indicated that similar mechanisms are utilized by L. pneumophila to replicate within two evolutionarily distant hosts. Although some mechanisms of attachment to both host cells were similar, other distinct mechanisms were utilized by L. pneumophila to attach to A. polyphaga. Our data supported the hypothesis that preadaptation of L. pneumophila to infection of protozoa may play a major role in its ability to replicate within mammalian cells and cause Legionnaires' disease.

The modulation of host cell apoptosis by intracellular bacterial pathogens

Recent years have witnessed significant advances in unraveling the elegant mechanisms by which intracellular bacterial pathogens induce and/or block apoptosis, which can influence disease progression. This intriguing aspect of the host-pathogen interaction adds another fascinating dimension to our understanding of the exploitation of host cell biology by intracellular bacterial pathogens.

From protozoa to mammalian cells: a new paradigm in the life cycle of intracellular bacterial pathogens

It is becoming apparent that several intracellular bacterial pathogens of humans can also survive within protozoa. This interaction with protozoa may protect these pathogens from harsh conditions in the extracellular environment and enhance their infectivity in mammals. This relationship has been clearly established in the case of the interaction between Legionella pneumophila and its protozoan hosts. In addition, the adaptation of bacterial pathogens to the intracellular life within the primitive eukaryotic protozoa may have provided them with the means to infect the more evolved mammalian cells. This is evident from the existence of several similarities, at both the phenotypic and the molecular levels, between the infection of mammalian and protozoan cells by L. pneumophila. Thus, protozoa appear to play a central role in the transition of bacteria from the environment to mammals. In essence, protozoa may be viewed as a 'biological gym', within which intracellular bacterial pathogens train for their encounters with the more evolved mammalian cells. Thus, intracellular bacterial pathogens have benefited from the structural and biochemical conservation of cellular processes in eukaryotes. The interaction of intracellular bacterial pathogens and protozoa highlights this conservation and may constitute a simplified model for the study of these pathogens and the evolution of cellular processes in eukaryotes. Furthermore, in addition to being environmental reservoirs for known intracellular pathogens of humans and animals, protozoa may be sources of emerging pathogenic bacteria. It is thus critical to re-examine the relationship between bacteria and protozoa to further our understanding of current human bacterial pathogenesis and, possibly, to predict the appearance of emerging pathogens.

Apoptosis in macrophages and alveolar epithelial cells during early stages of infection by Legionella pneumophila and its role in cytopathogenicity

The hallmark of Legionnaires' disease is intracellular replication of Legionella pneumophila within cells in the alveolar spaces. Cytopathogenicity of this bacterium to the host cell has been well demonstrated, but the mechanisms of host cell death due to infection by L. pneumophila are not well understood. In this study, induction of apoptosis in macrophages and alveolar epithelial cells by L. pneumophila during early stages of infection was confirmed by using multiple criteria, including DNA fragmentation by agarose gel electrophoresis, terminal deoxynucleotidyltransferase-mediated dUTP nick end labeling, surface exposure of phosphatidylserine, and cellular morphology by transmission electron microscopy. Induction of nuclear apoptosis in L. pneumophila-infected macrophages is mediated by activation of the caspase cascade death machinery. We provide genetic and biochemical evidence that L. pneumophila-induced apoptosis in macrophages and alveolar epithelial cells does not require intracellular bacterial replication or new protein synthesis. In addition, extracellular L. pneumophila is capable of inducing apoptosis. Furthermore, induction of apoptosis by L. pneumophila correlates with cytopathogenicity. We conclude that L. pneumophila-induced apoptosis in macrophages and alveolar epithelial cells plays an important role in cytopathogenicity to the host cell during early stages of infection.

Temporal pore formation-mediated egress from macrophages and alveolar epithelial cells by Legionella pneumophila

Legionella pneumophila does not induce apoptosis in the protozoan host, but induces pore formation-mediated cytolysis after termination of intracellular replication (L.-Y. Gao and Y. Abu Kwaik, Environ. Microbiol. 2:79-90, 2000). In contrast to this single mode of killing of protozoa, we have recently proposed a biphasic model by which L. pneumophila kills macrophages, in which the first phase is manifested through the induction of apoptosis during early stages of the infection, followed by an independent and temporal induction of necrosis during late stages of intracellular replication. Here we show that, similar to the protozoan host, the induction of necrosis and cytolysis of macrophages by L. pneumophila is mediated by the pore-forming toxin or activity. This activity is temporally and maximally expressed only upon termination of bacterial replication and correlates with cytolysis of macrophages and alveolar epithelial cells in vitro. We have identified five L. pneumophila mutants defective in the pore-forming activity. The phagosomes harboring the mutants do not colocalize with the late endosomal or lysosomal marker Lamp-1, and the mutants replicate intracellularly similar to the parental strain. Interestingly, despite their prolific intracellular replication, the mutants are defective in cytotoxicity and are "trapped" within and fail to lyse and egress from macrophages and alveolar epithelial cells upon termination of intracellular replication. However, the mutants are subsequently released from the host cell, most likely due to apoptotic death of the host cell. Data derived from cytotoxicity assays, confocal laser scanning microscopy, and electron microscopy confirm the defect in the mutants to induce necrosis of macrophages and the failure to egress from the host cell. Importantly, the mutants are completely defective in acute lethality (24 to 48 h) to intratracheally inoculated A/J mice. We conclude that the pore-forming activity of L. pneumophila is not required for phagosomal trafficking or for intracellular replication. This activity is expressed upon termination of bacterial replication and is essential to induce cytolysis of infected macrophages to allow egress of intracellular bacteria. In addition, this activity plays a major role in pulmonary immunopathology in vivo.

Activation of caspase 3 during Legionella pneumophila-induced apoptosis

The hallmark of Legionnaires' disease is replication of Legionella pneumophila within cells in the alveolar spaces. The mechanisms by which L. pneumophila replicates intracellularly and kills the host cell are largely not understood. We have recently shown that within 3 h of initiation of the infection and prior to intracellular replication, L. pneumophila induces apoptosis in macrophages, alveolar epithelial cells, and peripheral blood monocytes, which correlates with cytopathogenicity (L.-Y. Gao and Y. Abu Kwaik, Infect. Immun. 67:862-870, 1999). In this report, we show that the ability of L. pneumophila to induce apoptosis is, largely, not growth phase regulated. We demonstrate that the induction of apoptosis by L. pneumophila in macrophages is mediated through the activation of caspase 3. The enzymatic activity of caspase 3 to cleave a specific synthetic substrate in vitro is detected in L. pneumophila-infected macrophages at 2 h after infection and is maximal at 3 h, with over 900% increase in activity. The activity of caspase 3 to cleave a specific substrate [poly(ADP-ribose) polymerase, or PARP] in vivo is also detected at 2 h and is maximal at 3 h postinfection. The activity of caspase 3 to cleave the synthetic substrate in vitro and PARP in vivo is blocked by a specific inhibitor of caspase 3. The kinetics of caspase 3 activation correlates with that of L. pneumophila-induced nuclear apoptosis. Inhibition of caspase 3 activity blocks L. pneumophila-induced nuclear apoptosis and cytopathogenicity during early stages of the infection. Consistent with the ability to induce apoptosis, extracellular L. pneumophila also activates caspase 3. Three dotA/icmWXYZ mutants of L. pneumophila that are defective in inducing apoptosis do not induce caspase 3 activation, suggesting that expression and/or export of the apoptosis-inducing factor(s) is regulated by the dot/icm virulence system. This is the first description of the role of caspase 3 activation in induction of nuclear apoptosis in the host cell infected by a bacterial pathogen.

The mechanism of killing and exiting the protozoan host Acanthamoeba polyphaga by Legionella pneumophila

The ability of Legionella pneumophila to cause legionnaires' disease is dependent on its capacity to replicate within cells in the alveolar spaces. The bacteria kill mammalian cells in two phases: induction of apoptosis during the early stages of infection, followed by an independent and rapid necrosis during later stages of the infection, mediated by a pore-forming activity. In the environment, L. pneumophila is a parasite of protozoa. The molecular mechanisms by which L. pneumophila kills the protozoan cells, after their exploitation for intracellular proliferation, are not known. In an effort to decipher these mechanisms, we have examined induction of both apoptosis and necrosis in the protozoan Acanthamoeba polyphaga upon infection by L. pneumophila. Our data show that, although A. polyphaga undergoes apoptosis following treatment with actinomycin D, L. pneumophila does not induce apoptosis in these cells. Instead, intracellular L. pneumophila induces necrotic death in A. polyphaga, which is mediated by the pore-forming activity. Mutants of L. pneumophila defective in expression of the pore-forming activity are indistinguishable from the parental strain in intracellular replication within A. polyphaga. The parental strain bacteria cause necrosis-mediated lysis of all the A. polyphaga cells within 48 h after infection, and all the intracellular bacteria are released into the tissue culture medium. In contrast, all cells infected by the mutants remain intact, and the intracellular bacteria are 'trapped' within A. polyphaga after the termination of intracellular replication. Failure to exit the host cell after termination of intracellular replication results in a gradual decline in the viability of the mutant strain bacteria within A. polyphaga starting 48h after infection. Our data show that the pore-forming activity of L. pneumophila is not required for intracellular bacterial replication within A. polyphaga but is required for killing and exiting the protozoan host upon termination of intracellular replication.

Transcriptional regulation of the macrophage-induced gene (gspA) of Legionella pneumophila and phenotypic characterization of a null mutant

Expression of the global stress protein gene (gspA) is induced during the intracellular infection of macrophages and upon exposure of Legionella pneumophila to in vitro stress stimuli. Transcription of gspA is regulated by two promoters, one of which is regulated by the sigma 32 heat-shock transcription factor. We utilized a gspA promoter fusion to a promoter less lacZ to probe the phagososmal 'microenvironment' for the kinetics of exposure of intracellular L. pneumophila to stress stimuli. Expression through the gspA promoter was constitutively induced by approx. 16-fold throughout the intracellular infection, and occurred predominantly through the sigma 32-regulated promoter. Expression of the gspA promoter was induced approx. 4.5-fold, 5-, 11- and 9-fold upon exposure of L. pneumophila to heat shock, oxidative stress, acid shock, and osmotic shock, respectively. An isogenic insertion mutant of L. pneumophila in gspA (strain AA224) was constructed by allelic exchange in the wild-type strain AA200. Compared to in vitro-grown wild-type strain AA200, AA224 was more susceptible to all four in vitro stress stimuli. The wild-type phenotypes were restored to strain AA224 by complementation with a plasmid containing wild-type gspA. There was no difference between the wild-type strain and the gspA mutant in cytopathogenicity to U937 cells or in their kinetics of intracellular replication within macrophages and amoebae. However, compared to in vitro-grown bacteria, macrophage-grown and amoebae-grown AA200 and AA224 showed an equal and dramatic increase in resistance to in vitro stress stimuli. Our data showed that regardless of the capacity of L. pneumophila to subvert the microbicidal mechanisms of the macrophage, intracellular L. pneumophila is exposed to a high level of stress stimuli throughout the intracellular infection. Although the GspA protein is required for protection of the bacteria against in vitro stress stimuli, and is induced during intracellular multiplication, the loss of its function is probably compensated for by other macrophage-induced and stress-induced proteins within the intracellular environment.

Identification of macrophage-specific infectivity loci (mil) of Legionella pneumophila that are not required for infectivity of protozoa

We have recently shown that many mutants of Legionella pneumophila exhibit similar defective phenotypes within both U937 human-derived macrophages and the protozoan host Acanthamoeba (L.-Y. Gao, O. S. Harb, and Y. Abu Kwaik, Infect. Immun. 65:4738-4746, 1997). These observations have suggested that many of the mechanisms utilized by L. pneumophila to parasitize mammalian and protozoan cells are similar, but our data have not excluded the possibility that there are unique mechanisms utilized by L. pneumophila to survive and replicate within macrophages but not protozoa. To examine this possibility, we screened a bank of 5,280 miniTn10::kan transposon insertion mutants of L. pneumophila for potential mutants that exhibited defective phenotypes of cytopathogenicity and intracellular replication within macrophage-like U937 cells but not within Acanthamoeba polyphaga. We identified 32 mutants with various degrees of defects in cytopathogenicity, intracellular survival, and replication within human macrophages, and most of the mutants exhibited wild-type phenotypes within protozoa. Six of the mutants exhibited mild defects in protozoa. The defective loci were designated mil (for macrophage-specific infectivity loci). Based on their intracellular growth defects within macrophages, the mil mutants were grouped into five phenotypic groups. Groups I to III included the mutants that were severely defective in macrophages, while members of the other two groups exhibited a modestly defective phenotype within macrophages. The growth kinetics of many mutants belonging to groups I to III were also examined, and these were shown to have a similar defective phenotype in peripheral blood monocytes and a wild-type phenotype within another protozoan host, Hartmannella vermiformis. Transmission electron microscopy of A. polyphaga infected by three of the mil mutants belonging to groups I and II showed that they were similar to the parent strain in their capacity to recruit the rough endoplasmic reticulum (RER) around the phagosome. In contrast, infection of macrophages showed that the three mutants failed to recruit the RER around the phagosome during early stages of the infection. None of the mil mutants was resistant to NaCl, and the dot or icm NaCl(r) mutants are severely defective within mammalian and protozoan cells. Our data indicated that in addition to differences in mechanisms of uptake of L. pneumophila by macrophages and protozoa, there were also genetic loci required for L. pneumophila to parasitize mammalian but not protozoan cells. We hypothesize that L. pneumophila has evolved as a protozoan parasite in the environment but has acquired loci specific for intracellular replication within macrophages. Alternatively, ecological coevolution with protozoa has allowed L. pneumophila to possess multiple redundant mechanisms to parasitize protozoa and that some of these mechanisms do not function within macrophages.

Heterogeneity in the attachment and uptake mechanisms of the Legionnaires' disease bacterium, Legionella pneumophila, by protozoan hosts

Invasion and intracellular replication of Legionella pneumophila within protozoa in the environment plays a major role in the transmission of Legionnaires' disease. Intracellular replication of L. pneumophila within protozoa occurs in a rough endoplasmic reticulum (RER)-surrounded phagosome (Y. Abu Kwaik, Appl. Environ. Microbiol. 62:2022-2028, 1996). Since the subsequent fate of many intracellular pathogens is determined by the route of entry, we compared the mechanisms of attachment and subsequent uptake of L. pneumophila by the two protozoa Hartmannella vermiformis and Acanthamoeba polyphaga. Our data provide biochemical and genetic evidence that the mechanisms of attachment and subsequent uptake of L. pneumophila by the two protozoan hosts are, in part, different. First, uptake of L. pneumophila by H. vermiformis is completely blocked by the monovalent sugars galactose and N-acetyl-D-galactosamine, but these sugars partially blocked A. polyphaga. Second, attachment of L. pneumophila to H. vermiformis is associated with a time-dependent and reversible tyrosine dephosphorylation of multiple host proteins. In contrast, only a slight dephosphorylation of a 170-kDa protein of A. polyphaga is detected upon infection. Third, synthesis of H. vermiformis proteins but not of A. polyphaga proteins is required for uptake of L. pneumophila. Fourth, we have identified L. pneumophila mutants that are severely defective in attachment to A. polyphaga but which exhibit minor reductions in attachment to H. vermiformis and, thus, provide a genetic basis for the difference in mechanisms of attachment to both protozoa. The data indicate a remarkable adaptation of L. pneumophila to attach and invade different protozoan hosts by different mechanisms, yet invasion is followed by a remarkably similar intracellular replication within a RER-surrounded phagosome and subsequent killing of the host cell.

Different fates of Legionella pneumophila pmi and mil mutants within macrophages and alveolar epithelial cells

Alveolar epithelial cells, which constitute the majority of the alveolar surface, may represent a potential niche for intracellular replication of Legionella pneumophila that has been largely overlooked. We examined the phenotypes of a bank of 121 macrophage-defective mutants of L. pneumophila (designated as pmi and mil) for their cytopathogenicity to and intracellular survival and replication within human alveolar epithelial cells. Our data showed that 91 of 121 mutants that were defective (modest-severe) in macrophages exhibited wild type-like phenotypes in human type I alveolar epithelial cells. In contrast, the other 30 mutants were defective in both macrophages and alveolar epithelial cells. Transmission electron microscopy of the intracellular infection by three mutants showed that the defect in intracellular replication in macrophages and epithelial cells was associated with a defect in recruitment of the RER around the phagosome. Differences in attachment to macrophages and epithelial cells were also exhibited by some of the mutants. Pulmonary infection studies of A/J mice showed that a mutant defective in macrophages but not in alveolar epithelial cells replicated like the wild type strain in the lungs of A/J mice. In contrast, a mutant defective in both macrophages and alveolar epithelial cells failed to replicate and was killed. We conclude that certain distinct genetic loci of L. pneumophila are uniquely required for intracellular survival and replication within phagocytic but not epithelial cells, which may be important in vivo.

Heterogeneity in intracellular replication and cytopathogenicity of Legionella pneumophila and Legionella micdadei in mammalian and protozoan cells

In contrast to Legionella pneumophila, little is known about the pathogenesis of other legionellae species that are capable of causing Legionnaires' disease. In this report, we contrast L. pneumophila and L. micdadei for their cytopathogenicity and intracellular replication within mammalian and protozoan cells. We show by transmission electron microscopy that L. micdadei replicates within an endoplasmic reticulum (RER)-free phagosome within human macrophages, alveolar epithelial cells, and within the protozoan Hartmannella vermiformis. In contrast, L. pneumophila replicates within a RER-surrounded phagosome within the same host cells. In contrast to replication of L. pneumophila within Acanthamoebae polyphaga, L. micdadei does not replicate within this protozoan host. Despite the prolific intracellular replication, L. micdadei is less cytopathogenic to all host cells than L. pneumophila. Since both species replicate intracellularly to a similar level, we have examined whether the reduced cytopathogenicity of L. micdadei is due to a reduced capacity to induce apoptosis or pore formation-mediated necrosis, both of which contribute to killing of the host cell by L. pneumophila. The data show that both species induced apoptosis-mediated killing of mammalian cells to a similar level. In contrast to L. pneumophila, expression of the pore-forming toxin by L. micdadei and its necrotic effect on macrophages and alveolar epithelial cells is undetectable. This has been further confirmed showing that L. micdadei is completely defective in contact-dependent haemolysis of RBCs, an activity mediated by the pore-forming toxin. Finally, in contrast to L. pneumophila, there was no significant intrapulmonary replication of L. micdadei in the A/J mice animal model. Our data show dramatic differences between L. pneumophila and L. micdadei in intracellular replication, cytopathogenicity, and infectivity to mammalian and protozoan cells.

Identification of putative cytoskeletal protein homologues in the protozoan host Hartmannella vermiformis as substrates for induced tyrosine phosphatase activity upon attachment to the Legionnaires' disease bacterium, Legionella pneumophila

The Legionnaires' disease bacterium, Legionella pneumophila, is a facultative intracellular pathogen that invades and replicates within two evolutionarily distant hosts, free living protozoa and mammalian cells. Invasion and intracellular replication within protozoa are thought to be major factors in the transmission of Legionnaires' disease. We have recently reported the identification of a galactose/N-acetyl-D-galactosamine (Gal/GalNAc) lectin in the protozoan host Hartmannella vermiformis as a receptor for attachment and invasion by L. pneumophila (Venkataraman, C., B.J. Haack, S. Bondada, and Y.A. Kwaik. 1997. J. Exp. Med. 186:537-547). In this report, we extended our studies to the effects of bacterial attachment and invasion on the cytoskeletal proteins of H. vermiformis. We first identified the presence of many protozoan cytoskeletal proteins that were putative homologues to their mammalian counterparts, including actin, pp125(FAK), paxillin, and vinculin, all of which were basally tyrosine phosphorylated in resting H. vermiformis. In addition to L. pneumophila-induced tyrosine dephosphorylation of the lectin, bacterial attachment and invasion was associated with tyrosine dephosphorylation of paxillin, pp125(FAK), and vinculin, whereas actin was minimally affected. Inhibition of bacterial attachment to H. vermiformis by Gal or GalNAc monomers blocked bacteria-induced tyrosine dephosphorylation of detergent-insoluble proteins. In contrast, inhibition of bacterial invasion but not attachment failed to block bacteria-induced tyrosine dephosphorylation of H. vermiformis proteins. This was further supported by the observation that 10 mutants of L. pneumophila that were defective in invasion of H. vermiformis were capable of inducing tyrosine dephosphorylation of H. vermiformis proteins. Entry of L. pneumophila into H. vermiformis was predominantly mediated by noncoated receptor-mediated endocytosis (93%) but coiling phagocytosis was infrequently observed (7%). We conclude that attachment but not invasion by L. pneumophila into H. vermiformis was sufficient and essential to induce protein tyrosine dephosphorylation in H. vermiformis. These manipulations of host cell processes were associated with, or followed by, entry of the bacteria by a noncoated receptor-mediated endocytosis. A model for attachment and entry of L. pneumophila into H. vermiformis is proposed.

Signal transduction in the protozoan host Hartmannella vermiformis upon attachment and invasion by Legionella micdadei

The intracellular pathogens Legionella micdadei and Legionella pneumophila are the two most common Legionella species that cause Legionnaires' disease. Intracellular replication within pulmonary cells is the hallmark of Legionnaires' disease. In the environment, legionellae are parasites of protozoans, and intracellular bacterial replication within protozoans plays a major role in the transmission of Legionnaires' disease. In this study, we characterized the initial host signal transduction mechanisms involved during attachment to and invasion of the protozoan host Hartmannella vermiformis by L. micdadei. Bacterial attachment prior to invasion of H. vermiformis by L. micdadei is associated with tyrosine dephosphorylation of multiple host cell proteins, including a 170-kDa protein. We have previously shown that this 170-kDa protein is the galactose N-acetylgalactosamine (Gal/GalNAc)-inhibitable lectin receptor that mediates attachment to and invasion of H. vermiformis by L. pneumophila. Subsequent bacterial entry targets L. micdadei into a phagosome that is not surrounded by the rough endoplasmic reticulum (RER). In contrast, uptake of L. pneumophila mediated by attachment to the Gal/GalNAc lectin is followed by targeting of the bacterium into an RER-surrounded phagosome. These results indicate that despite similarities in the L. micdadei and L. pneumophila attachment-mediated signal transduction mechanisms in H. vermiformis, the two bacterial species are targeted into morphologically distinct phagosomes in their natural protozoan host.

Molecular characterization of HMW-GS 1Dx3(t) and 1Dx4(t) genes from Aegilops tauschii and their potential value for wheat quality improvement

Two x-type high molecular weight glutenin subunits (HMW-GS) in Aegilops tauschii, 1Dx3(t) and 1Dx4(t) were identified by SDS-PAGE and MALDI-TOF-MS. Their complete coding sequences were isolated by AS-PCR. 1Dx3(t) and 1Dx4(t) genes consist of 2535 bp and 2508 bp and encode 845 and 836 amino acid residues, respectively. The deduced molecular masses of 1Dx3(t) and 1Dx4(t) gene products are 87655.26 Da and 86664.24 Da, respectively, well corresponding to the molecular masses measured by MALDI-TOF-MS. A total of 18 SNPs were identified between 1Dx3(t) and 1Dx4(t). Comparing with 1Dx5 subunit, 1Dx3(t) had a six amino acid insertion at 146-151 while the 1Dx4(t) had a nine amino acid deletion when compared with 1Dx3(t) subunit. The authenticity of the cloned 1Dx3(t) and 1Dx4(t) genes were confirmed by successful expression of their ORFs in E. coli. Comparison and phylogenetic tree based on the amino acid and nucleotide sequences confirmed that 1Dx3(t) was most closely related to 1Dx5 subunit that is widely accepted as a superior subunit for bread-making property. The secondary structure prediction demonstrated that 1Dx3(t) subunit has significantly high α-helix and β-strand contents, suggesting it might have positive effects on dough quality.

Molecular characterization and comparative transcriptional analysis of LMW-m-type genes from wheat (Triticum aestivum L.) and Aegilops species

Twelve new LMW-GS genes were characterized from bread wheat (Triticum aestivum L.) cultivar Zhongyou 9507 and five Aegilops species by AS-PCR. These genes belong to the LMW-m type and can be classified into two subclasses designated as 1 and 2, with the latter predominant in both wheat and related wild species. Genes in the two subclasses were significantly different from each other in SNPs and InDels variations. In comparison to subclass 1, the structural features of subclass 2 differs in possessing 21 amino acid residue substitutions, two fragment deletions (each with 7 amino acid residues), and a double-residue deletion and two fragment insertions (12 and 2-5 residues). Phylogenetic analysis revealed that the two subclasses were divergent at about 6.8 MYA, earlier than the divergence of C, M, N, S(s) and U genomes. The S(s) and B genomes displayed a very close relationship, whereas the C, M, N and U genomes appeared to be related to the D genome of bread wheat. The presently characterized genes ZyLMW-m1 and ZyLMW-m2 from Zhongyou 9507 were assigned to the D genome. Moreover, these genes were expressed successfully in Escherichia coli. Their transcriptional levels during grain developmental stages detected by quantitative real-time PCR (qRT-PCR) showed that both genes started to express at 5 days post-anthesis (DPA), reaching the maximum at 14 DPA after which their expressions decreased. Furthermore, the expression level of ZyLMW-m2 genes was much higher than that of ZyLMW-m1 during all grain developmental stages, suggesting that the expression efficiency of LMW-GS genes between the two subclasses was highly discrepant.

Decline in intrahepatic cccDNA and increase in immune cell reactivity after 12 weeks of antiviral treatment were associated with HBeAg loss

Viral load reduction facilitates recovery of antiviral T-cell responses. Dynamic alterations in intrahepatic viraemia clearance and immune cell reactivity during the early phase of nucleoside analogue (NA) therapy and the impact of these changes on HBeAg seroconversion are unknown. Fifteen HBeAg-positive chronic hepatitis B (CHB) patients were treated with adefovir dipivoxil. T-cell reactivity to HBV core and surface antigens were tested using ELISPOT assay from baseline to week 48 post-treatment (at 4-week intervals). Before and at week 12 of treatment, paired liver biopsies were analysed for intrahepatic HBV-DNA and cccDNA via real-time fluorescent PCR. In situ detection of CD4(+) , CD8(+) T cells and NK cells was analysed by immunohistochemistry. With viral load reduction, HBV-specific IFN-γ-producing CD4(+) T cells in patients with HBeAg loss were greatly enhanced and reached the highest level at week 12, with further increase observed between week 36 and week 48. After 12 weeks of treatment, total intrahepatic HBV-DNA and cccDNA had significantly decreased; however, there was no difference in the viral loads or extent of reduction between patients with and without HBeAg loss. Paralleling reduction in viral load, intrahepatic CD8(+) T lymphocytes increased in patients with HBeAg loss compared with baseline values. Only one patient without HBeAg loss exhibited similar results. Increased immune cells were observed in certain patients along with reduced hepatic viral loads during the second phase of HBV-DNA decline, which could promote the recovery of antiviral immunity and facilitate HBeAg loss.

Preparation and maintenance of SCID-hu mice for HIV research

The SCID-hu mouse bearing a functional human thymic implant can be easily infected with HIV. Infection results in virus replication and relatively rapid depletion of CD4+ human thymocytes, resulting in a pathologic profile similar to that seen in the thymus of HIV-infected humans. The use of the SCID-hu model for HIV research requires protection of the animals from opportunistic infections and protection of the operators from human pathogens. This discussion describes reliable methods of animal care and surgical procedures to meet these needs.

Dissecting the Genetic Architecture of Melon Chilling Tolerance at the Seedling Stage by Association Mapping and Identification of the Elite Alleles

Low temperature is an important abiotic stress that negatively affects morphological growth and fruit development in melon (Cucumis melo L.). Chilling stress at the seedling stage causes seedling injury and poor stand establishment, prolonging vegetative growth and delaying fruit harvest. In this study, association mapping was performed for chilling tolerance at the seedling stage on an expanded melon core collection containing 212 diverse accessions by 272 SSRs and 27 CAPSs. Chilling tolerance of the melon seedlings was evaluated by calculating the chilling injury index (CII) in 2016 and 2017. Genetic diversity analysis of the whole accession panel presented two main groups, which corresponded to the two subspecies of C. melo, melo, and agrestis. Both the subspecies were sensitive to chilling but with agrestis being more tolerant. Genome-wide association study (GWAS) was conducted, respectively, on the whole panel and the two subspecies, totally detecting 51 loci that contributed to 74 marker-trait associations. Of these associations, 35 were detected in the whole panel, 21 in melo, and 18 in agrestis. About half of the associations identified in the two subspecies were also observed in the whole panel, and seven associations were shared by both the subspecies. CMCT505_Chr.1 was repeatedly detected in different populations with high phenotypic contribution and could be a key locus controlling chilling tolerance in C. melo. Nine loci were selected for evaluation of the phenotypic effects related to their alleles, which identified 11 elite alleles contributing to seedling chilling tolerance. Four such alleles existed in both the subspecies and six in either of the two subspecies. Analysis of 20 parental combinations for their allelic status and phenotypic values showed that the elite alleles collectively contributed to enhancement of the chilling tolerance. Tagging the loci responsible for chilling tolerance may simultaneously favor dissecting the complex adaptability traits and elevate the efficiency to improve chilling tolerance using marker-assisted selection in melon.

Association between the rs189037 single nucleotide polymorphism in the ATM gene promoter and cognitive impairment

The aim of this study was to explore the existence of a relationship between the rs189037 single nucleotide polymorphism (SNP) of the ataxia telangiectasia mutated (ATM) gene and cognitive impairment in the elderly (aged 60 years and above). In a cohort, 505 residents of Suinung City were consecutively recruited and their cognitive function was measured using a 30-point Mini-Mental State Examination (MMSE). The subjects were divided into cognitive impairment group and control group on the basis of MMSE scores. Presence of the rs189037 SNP variant was examined using polymerase chain reaction-restriction fragment length polymorphism. The prevalence rates of cognitive impairment were 32.7% in the whole sample. The genotype frequencies of the rs189037 polymorphism were 33.5% (CC), 50.7% (CT), and 15.8% (TT); the C and T allele frequencies were 58.8 and 41.2%, respectively. No significant differences in the frequency distributions of the CC, CT and TT genotypes were observed between cognitively impaired and control groups. We found that the rs189037 SNP was not directly correlated with cognitive impairment among the elderly Chinese Han population.

Celiac disease is not increased in women with hip fractures and low vitamin D levels

OBJECTIVE

Celiac disease is associated with decreased bone density; however, the risk of fractures in celiac disease patients is unclear. We compared the prevalence of celiac disease between a group of women with hip fractures and a group of women undergoing elective joint replacement surgery and the association between celiac disease and vitamin D levels.

METHODS

Two hundred eight community dwelling and postmenopausal women were recruited from Boston, MA (n=81) and Baltimore, MD (n=127). We measured tissue transglutaminase IgA by ELISA to diagnose celiac disease and 25-hydroxyvitamin D (25(OH)D) levels by radioimmunoassay in both women with hip fractures (n=157) and a control group (n=51) of total hip replacement subjects from Boston. Subjects were excluded if they took any medications or had medical conditions that might affect bone.

RESULTS

Median serum 25(OH)D levels were significantly lower (p< 0.0001) in the hip fracture cohorts compared to the elective joint replacement cohort (14.1 ng/ml vs. 21.3 ng/ml, respectively). There were no differences in the percentage of subjects with a positive tissue transglutaminase in the women with hip fractures versus the control group (1.91% vs. 1.96%, respectively).

CONCLUSION

Vitamin D levels are markedly reduced in women with hip fractures, however hip fracture patients did not show a higher percentage of positive tissue transglutaminase levels compared with controls. These data suggest that routine testing for celiac disease among hip fracture patients may not be necessary in the absence of clinical signs and symptoms, although data from larger studies among hip fracture subjects are needed.

[Study on the clinical significance and correlation of arginase-1 and inducible nitric oxide synthase expression in hepatocellular carcinoma]

Objective: To investigate the clinical significance and correlation of arginase 1 (Arg-1) and inducible nitric oxide synthase (iNOS) expression in hepatocellular carcinoma (HCC). Methods: The expression of Arg-1and iNOS in 146 cases of hepatocellular carcinoma tissues and corresponding adjacent tissues was detected by immunohistochemistry. The clinicopathological characteristics and the correlation between the expressions and prognosis were determined by chi square test, Spearman's rank correlation, Kaplan-Meier survival analysis and Cox regression analysis. Results: The positive rates of Arg-1 and iNOS were 18.7% (23/123) and 37.0% (54/146), respectively, which was significantly lower than the adjacent tissues [100%(146/146) and 93.8% (137/146)] and the difference was statistically significant (χ (2) = 212.521, P < 0.01, χ (2) = 104.276, P < 0.01). There was a positive correlation between the both expression (r = 0.331, P < 0.01). Arg-1 low expression was correlated with preoperative serum alpha-fetoprotein (AFP) level, tumor size, differentiation degree, histological types and Edmondson's grade. iNOS low expression was correlated with the differentiation degree and Edmondson's grade (P < 0.05). Kaplan Meier survival analysis showed that in patients with recurrence-free survival (RFs), Arg-1 (+) group > Arg-1 (-) group and Arg-1 (+) iNOS (+) group > Arg-1 (+) iNOS (-) group > Arg-1 (-) iNOS (-) group (P < 0.05). Cox multivariate analysis showed that age, tumor size, Edmondson's grade, vascular tumor emboli were significantly correlated with RFs (P < 0.05). Conclusion: There is a positive correlation between Arg-1 and iNOS expressions in HCC, and both may reflect the HCC malignant degree. The reduced/absent expression of both may participate in the occurrence and development of HCC. The combined detection of Arg-1 and iNOS on HCC may have certain significance for the judgment of differentiation degree and prognosis.