Rapid early onset lymphocyte cell death in mice resistant, but not susceptible to Leishmania major infection

Leishmania major (Lm) infection in mice is a prototypical model for the role of immune deviation in disease resistance. Resistant strains of mice develop a Th1 response to Lm infection, distinguished by secretion of IL-12 and interferon . In contrast, susceptible strains display sustained IL-4 expression characteristic of a Th2 response. However, when mechanisms of cell death are blocked, mice display a susceptible phenotype even in the presence of a strong Th1 response, suggesting that cell death, and not cytokine bias, may be an importnt factor in disease resistance. Here, we investigated this hypothesis by comparing lymphocyte cellularity, cell death and Fas expression in resistant CBA and susceptible BALB/c mice during the course of Lm infection. We found that delayed onset of cell death and late Fas induction correlated with massive lymphocyte accumulation and susceptibility to leishmaniasis, while early cell death and rapid Fas induction occurred in resistant mice.     

Mitochondrial genome content is regulated during nematode development

Growth and development rely on the mitochondrial respiratory chain (MRC) as the major source of ATP. We measured the mitochondrial DNA (mtDNA) copy number of each of the Caenorhabditis elegans developmental stages. Embryos, L1, L2, and L3 larvae all have approximately 25,000 copies of maternally derived mtDNA. The copy number increases fivefold in L4 larvae and a further sixfold in adult hermaphrodites, but only twofold in adult males. The majority of mtDNA in adult worms is germline associated, and germline-deficient mutants show markedly reduced mtDNA contents. With sperm-deficient or oocyte-deficient mutants, we confirm that mtDNA amplification is primarily associated with oocyte production. When mtDNA replication is inhibited, a quantitative and homogeneous arrest as L3 larvae occurs. Thus, mtDNA amplification is a necessary component of normal development and its regulation may involve an energy-sensing decision or checkpoint that can be invoked when mitochondrial energy generation is impaired.     

Ndrg4 is required for normal myocyte proliferation during early cardiac development in zebrafish

NDRG4 is a novel member of the NDRG family (N-myc downstream-regulated gene). The roles of NDRG4 in development have not previously been evaluated. We show that, during zebrafish embryonic development, ndrg4 is expressed exclusively in the embryonic heart, the central nervous system (CNS) and the sensory system. Ndrg4 knockdown in zebrafish embryos causes a marked reduction in proliferative myocytes and results in hypoplastic hearts. This growth defect is associated with cardiac phenotypes in morphogenesis and function, including abnormal heart looping, inefficient circulation and weak contractility. We reveal that ndrg4 is required for restricting the expression of versican and bmp4 to the developing atrioventricular canal. This constellation of ndrg4 cardiac defects phenocopies those seen in mutant hearts of heartstrings (hst), the tbx5 loss-of-function mutants in zebrafish. We further show that ndrg4 expression is significantly decreased in hearts with reduced tbx5 activities. Conversely, increased expression of tbx5 that is due to tbx20 knockdown leads to an increase in ndrg4 expression. Together, our studies reveal an essential role of ndrg4 in regulating proliferation and growth of cardiomyocytes, suggesting that ndrg4 may function downstream of tbx5 during heart development and growth.     

Haemonchus contortus and Trichostrongylus colubriformis did not adapt to long-term exposure to sheep that were genetically resistant or susceptible to nematode infections

We tested the hypothesis that Haemonchus contortus and Trichostrongylus colubriformis would adapt to long-term exposure to sheep that were either genetically resistant or susceptible to H. contortus. Sheep genotypes were from lines with 10 years prior selection for low (resistant, R) or high (susceptible, S) faecal worm egg count (WEC) following H. contortus infection. Long-term exposure of H. contortus and T.colubriformis to R or S genotypes was achieved using serial passage for up to 30 nematode generations. Thus, we generated four nematode strains; one strain of each species solely exposed to R sheep and one strain of each species solely exposed to S sheep. Considerable host genotype differences in mean WEC during serial passage confirmed adequate nematode selection pressure for both H. contortus (R 4900 eggs per gram (epg), S 19,900 epg) and T. colubriformis (R 5300 epg, S 13,500 epg). Adaptation of nematode strain to host genotype was tested using seven cross-classified tests for H. contortus, and two cross-classified and one outbred genotype test for T. colubriformis. In the cross-classified design, where each strain infects groups of R, S or randomly bred control sheep, parasite adaptation would be indicated by a significant host genotype by nematode strain interaction for traits indicating parasite reproductive success; specifically WEC and, for H. contortus strains, packed cell volume. We found no significant evidence of parasite adaptation to host genotype (P > 0.05) for either the H. contortus or T. colubriformis strains. Therefore, we argue that nematodes will not adapt quickly to sheep bred for nematode resistance, where selection is based on low WEC, although selecting sheep using a subset of immune functions may increase adaptation risk. Our results support the hypothesis that nematode resistance is determined by many genes each with relatively small effect. In conclusion, selection of sheep for nematode resistance using WEC should be sustainable in the medium to long-term.     

The murine model of infection with Leishmania major and its importance for the deciphering of mechanisms underlying differences in Th cell differentiation in mice from different genetic backgrounds

Mice from the majority of inbred strains are resistant to infection by Leishmania major, an obligate intracellular protozoan parasite of macrophages in the mammalian host. In contrast, mice from BALB strains are unable to control infection and develop progressive disease. In this model of infection, genetically determined resistance and susceptibility have been clearly shown to result from the appearance of parasite-specific CD4+ T helper 1 or T helper 2 cells, respectively. This murine model of infection is considered as one of the best experimental systems for the study of the mechanisms operating in vivo at the initiation of polarised T helper 1 and T helper 2 cell maturation. Among the several factors influencing Th cell development, cytokines themselves critically regulate this process. The results accumulated during the last years have clarified some aspects of the role played by cytokines in Th cell differentiation. They are providing critical information that may ultimately lead to the rational devise of means by which to tailor immune responses to the effector functions that are most efficient in preventing and/or controlling infections with pathogens.     

Mouse FGF15 is the ortholog of human and chick FGF19, but is not uniquely required for otic induction

The inner ear develops from an ectodermal placode that is specified by inductive signals from the adjacent neurectoderm and underlying mesoderm. In chick, fibroblast growth factor (Fgf)-19 is expressed in mesoderm underlying the presumptive otic placode, and human FGF19 induces expression of otic markers in a tissue explant containing neural plate and surface ectoderm. We show here that mouse Fgf15 is the sequence homolog of chick and human Fgf19/FGF19. In addition, we show that FGF15, like FGF19, is sufficient to induce expression of otic markers in a chick explant assay, suggesting that these FGFs are orthologs. Mouse embryos lacking Fgf15, however, do not have otic abnormalities at E9.5-E10.5, suggesting that Fgf15 is not uniquely required for otic induction or early patterning of the otocyst. To compare FGF15 and FGF19 signaling components and assess where signals potentially redundant with FGF15 might function, we determined the expression patterns of Fgf15 and Fgf19. Unlike Fgf19, Fgf15 is not expressed in mesoderm underlying the presumptive otic placode, but is expressed in the adjacent neurectoderm. Fgfr4, which encodes the likely receptor for both FGF19 and FGF15, is expressed in the neurectoderm of both species, and is also expressed in the mesoderm only in chick. These results suggest the hypotheses that during otic induction, FGF19 signals in either an autocrine fashion to the mesoderm or a paracrine fashion to the neurectoderm, whereas FGF15 signals in an autocrine fashion to the neurectoderm. Thus, the FGFs that signal to the neurectoderm are the best potential candidates for redundancy with FGF15 during mouse otic development.     

Syntrophin-2 is required for eye development in Drosophila

Syntrophins are components of the dystrophin glycoprotein complex (DGC), which is encoded by causative genes of muscular dystrophies. The DGC is thought to play roles not only in linking the actin cytoskeleton to the extracellular matrix, providing stability to the cell membrane, but also in signal transduction. Because of their binding to a variety of different molecules, it has been suggested that syntrophins are adaptor proteins recruiting signaling proteins to membranes and the DGC. However, critical roles in vivo remain elusive. Drosophila Syntrophin-2 (Syn2) is an orthologue of human γ1/γ2-syntrophins. Western immunoblot analysis here showed Syn2 to be expressed throughout development, with especially high levels in the adult head. Morphological aberrations were observed in Syn2 knockdown adult flies, with lack of retinal elongation and malformation of rhabdomeres. Furthermore, Syn2 knockdown flies exhibited excessive apoptosis in third instar larvae and alterations in the actin localization in the pupal retinae. Genetic crosses with a collection of Drosophila deficiency stocks allowed us to identify seven genomic regions, deletions of which caused enhancement of the rough eye phenotype induced by Syn2 knockdown. This information should facilitate identification of Syn2 regulators in Drosophila and clarification of roles of Syn2 in eye development.     

Retinoic acid signalling is required for specification of pronephric cell fate

The mechanisms by which a subset of mesodermal cells are committed to a nephrogenic fate are largely unknown. In this study, we have investigated the role of retinoic acid (RA) signalling in this process using Xenopus laevis as a model system and Raldh2 knockout mice. Pronephros formation in Xenopus embryo is severely impaired when RA signalling is inhibited either through expression of a dominant-negative RA receptor, or by expressing the RA-catabolizing enzyme XCyp26 or through treatment with chemical inhibitors. Conversely, ectopic RA signalling expands the size of the pronephros. Using a transplantation assay that inhibits RA signalling specifically in pronephric precursors, we demonstrate that this signalling is required within this cell population. Timed antagonist treatments show that RA signalling is required during gastrulation for expression of Xlim-1 and XPax-8 in pronephric precursors. Moreover, experiments conducted with a protein synthesis inhibitor indicate that RA may directly regulate Xlim-1. Raldh2 knockout mouse embryos fail to initiate the expression of early kidney-specific genes, suggesting that implication of RA signalling in the early steps of kidney formation is evolutionary conserved in vertebrates.     

Characterisation of the protective immune response following subcutaneous vaccination of susceptible mice against Trichuris muris

Trichuris muris is a laboratory model for the human whipworm Trichuris trichiura which infects approximately 1 billion people in tropical and sub-tropical countries. The development of a vaccine would control trichuriasis by promoting the acquisition of immunity during childhood, thereby reducing faecal egg output by the community into their environment. Resistance to T. muris, defined as expulsion of the parasite prior to patency, requires the development of a T helper 2 (Th2) response during a primary infection. To our knowledge this is the first study to describe the protective immune response in the peripheral lymph nodes (PLN), mesenteric lymph nodes (MLN) and colonic mucosa following s.c. vaccination against T. muris. Susceptible AKR mice were either vaccinated with T. muris excretory-secretory product (ES) in incomplete Freund’s adjuvant (IFA) (ES/IFA) or injected with PBS in IFA (PBS/IFA) and for protection experiments were infected with embryonated infective T. muris eggs 10 days later. The ES/IFA vaccine induced the proliferation of PLN cells and their production of Th2 cytokines and the Th1-associated cytokine IFN-γ. Following a challenge infection, the ES/IFA vaccination offered susceptible mice complete protection. While MLN-derived IFN-γ was produced by infected mice following either ES/IFA vaccination or PBS/IFA, the protection of susceptible mice by ES/IFA was characterised by the production of MLN-derived Th2 cytokines. Goblet cell hyperplasia and the influx and alternative activation of macrophages were observed locally in the gut post-challenge infection. The rate of epithelial turnover did not appear to be increased by vaccination, suggesting that there are differences in the mechanisms of expulsion between ‘natural resistance’ and ‘vaccinated resistance’. High levels of serum IgG1 and cell-bound IgG1 in the colon of mice protected by the ES/IFA vaccine suggest that antibody may be involved in vaccination-induced worm expulsion.     

Notch2 is required for maintaining sustentacular cell function in the adult mouse main olfactory epithelium

Notch receptors are expressed in neurons and glia in the adult nervous system, but why this expression persists is not well-understood. Here we examine the role of the Notch pathway in the postnatal mouse main olfactory system, and show evidence consistent with a model where Notch2 is required for maintaining sustentacular cell function. In the absence of Notch2, the laminar nature of these glial-like cells is disrupted. Hes1, Hey1, and Six1, which are downstream effectors of the Notch pathway, are down-regulated, and cytochrome P450 and Glutathione S-transferase (GST) expression by sustentacular cells is reduced. Functional levels of GST activity are also reduced. These disruptions are associated with increased olfactory sensory neuron degeneration. Surprisingly, expression of Notch3 is also down-regulated. This suggests the existence of a feedback loop where expression of Notch3 is initially independent of Notch2, but requires Notch2 for maintained expression. While the Notch pathway has previously been shown to be important for promoting gliogenesis during development, this is the first demonstration that the persistent expression of Notch receptors is required for maintaining glial function in adult.     

Fgf19 regulated by Hh signaling is required for zebrafish forebrain development

Fibroblast growth factor (Fgf) signaling plays important roles in brain development. Fgf3 and Fgf8 are crucial for the formation of the forebrain and hindbrain. Fgf8 is also required for the midbrain to form. Here, we identified zebrafish Fgf19 and examined its roles in brain development by knocking down Fgf19 function. We found that Fgf19 expressed in the forebrain, midbrain and hindbrain was involved in cell proliferation and cell survival during embryonic brain development. Fgf19 was also essential for development of the ventral telencephalon and diencephalon. Regional specification is linked to cell type specification. Fgf19 was also essential for the specification of gamma-aminobutyric acid (GABA)ergic interneurons and oligodendrocytes generated in the ventral telencephalon and diencephalon. The cross talk between Fgf and Hh signaling is critical for brain development. In the forebrain, Fgf19 expression was down-regulated on inhibition of Hh but not of Fgf3/Fgf8, and overexpression of Fgf19 rescued partially the phenotype on inhibition of Hh. The present findings indicate that Fgf19 signaling is crucial for forebrain development by interacting with Hh and provide new insights into the roles of Fgf signaling in brain development.