Population Genetic Structure and Conservation of the Lesser White-Fronted GooseAnser erythropus

The lesser white-fronted goose is a sub-Arctic species with a currently fragmented breeding range, which extends from Fennoscandia to easternmost Siberia. The population started to decline at the beginning of the last century and, with a current world population estimate of 25,000 individuals, it is the most threatened of the Palearctic goose species. Of these, only 30–50 pairs breed in Fennoscandia. A fragment of the control region of mtDNA was sequenced from 110 individuals from four breeding, one staging and two wintering areas to study geographic subdivisions and gene flow. Sequences defined 15 mtDNA haplotypes that were assigned to two mtDNA lineages. Both the mtDNA lineages were found from all sampled localities indicating a common ancestry and/or some level of gene flow. Analyses of molecular variance showed significant structuring among populations ( _ST 0.220, P < 0.001). The results presented here together with ecological data indicate that the lesser white-fronted goose is fragmented into three distinctive subpopulations, and thus, the conservation status of the species should be reconsidered.     

Making tubes: step by step

Branched hollow tubes form the architectural basis of many mammalian organs. The growth factor HGF/SF and its receptor, the Met receptor tyrosine kinase, stimulate epithelial cells to undergo tubulogenesis in vitro. In this issue of Developmental Cell, O'Brien et al. (2004) look at temporal regulation and the role of two HGF/SF effectors, the ERK 1/2 MAP kinases and matrix metalloproteases, in this process.     

Divergence in gene expression related to variation in host specificity of an ectomycorrhizal fungus

Ectomycorrhizae are formed by mutualistic interactions between fungi and the roots of woody plants. During symbiosis the two organisms exchange carbon and nutrients in a specific tissue that is formed at the contact between a compatible fungus and plant. There is considerable variation in the degree of host specificity among species and strains of ectomycorrhizal fungi. In this study, we have for the first time shown that this variation is associated with quantitative differences in gene expression, and with divergence in nucleotide sequences of symbiosis-regulated genes. Gene expression and sequence evolution were compared in different strains of the ectomycorrhizal fungus Paxillus involutus; the strains included Nau, which is not compatible with birch and poplar, and the two compatible strains Maj and ATCC200175. On a genomic level, Nau and Maj were very similar. The sequence identity was 98.9% in the 16 loci analysed, and only three out of 1075 genes analysed by microarray-based hybridizations had signals indicating differences in gene copy numbers. In contrast, 66 out of the 1075 genes were differentially expressed in Maj compared to Nau after contact with birch roots. Thirty-seven of these symbiosis-regulated genes were also differentially expressed in the ATCC strain. Comparative analysis of DNA sequences of the symbiosis-regulated genes in different strains showed that two of them have evolved at an enhanced rate in Nau. The sequence divergence can be explained by a decreased selection pressure, which in turn is determined by lower functional constraints on these proteins in Nau as compared to the compatible strains.     

Endogenous and dietary indoles: a class of antioxidants and radical scavengers in the ABTS assay

Indoles are very common in the body and diet and participate in many biochemical processes. A total of twenty-nine indoles and analogs were examined for their properties as antioxidants and radical scavengers against 2,2'-Azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) ABTS*+ radical cation. With only a few exceptions, indoles reacted nonspecifically and quenched this radical at physiological pH affording ABTS. Indoleamines like tryptamine, serotonin and methoxytryptamine, neurohormones (melatonin), phytohormones (indoleacetic acid and indolepropionic acid), indoleamino acids like L-tryptophan and derivatives (N-acetyltryptophan, L-abrine, tryptophan ethyl ester), indolealcohols (tryptophol and indole-3-carbinol), short peptides containing tryptophan, and tetrahydro-beta-carboline (pyridoindole) alkaloids like the pineal gland compound pinoline, acted as radical scavengers and antioxidants in an ABTS assay-measuring total antioxidant activity. Their trolox equivalent antioxidant capacity (TEAC) values ranged from 0.66 to 3.9 mM, usually higher than that for Trolox and ascorbic acid (1 mM). The highest antioxidant values were determined for melatonin, 5-hydroxytryptophan, trp-trp and 5-methoxytryptamine. Active indole compounds were consumed during the reaction with ABTS*+ and some tetrahydropyrido indoles (e.g. harmaline and 1-methyl-1,2,3,4-tetrahydro-beta-carboline-3-carboxylic acid ethyl ester) afforded the corresponding fully aromatic beta-carbolines (pyridoindoles), that did not scavenge ABTS*+. Radical scavenger activity of indoles against ABTS*+ was higher at physiological pH than at low pH. These results point out to structural compounds with an indole moiety as a class of radical scavengers and antioxidants. This activity could be of biological significance given the physiological concentrations and body distribution of some indoles.     

How to make tubes: signaling by the Met receptor tyrosine kinase

Hepatocyte growth factor/scatter factor (HGF/SF), acting through the receptor tyrosine kinase Met, stimulates cells derived from a variety of different organs to form elongated hollow tubules when grown in three-dimensional gels. In vivo data also indicate a role for HGF/SF and Met in tubule formation during liver and kidney regeneration and mammary gland formation. Activation of Met results in the recruitment of a myriad of signal transducers that regulate dissociation of adherens junctions and the stimulation of cellular motility, survival, proliferation and morphogenesis during tubule formation. Among these many signal transducers, the Gab1 adaptor protein and its effector, the SHP2 tyrosine phosphatase, have been found to be crucial for tubulogenesis and for the sustained stimulation of the ERK/MAP kinase pathway. Here, we discuss the contribution of these and other signaling pathways and the role of HGF/SF and Met in the formation of epithelial cell tubules both in vitro in branching-morphogenesis assays and in vivo during organogenesis.     

IFN-beta gene deletion leads to augmented and chronic demyelinating experimental autoimmune encephalomyelitis

Since the basic mechanisms behind the beneficial effects of IFN-beta in multiple sclerosis (MS) patients are still obscure, here we have investigated the effects of IFN-beta gene disruption on the commonly used animal model for MS, experimental autoimmune encephalomyelitis (EAE). We show that IFN-beta knockout (KO) mice are more susceptible to EAE than their wild-type (wt) littermates; they develop more severe and chronic neurological symptoms with more extensive CNS inflammation and demyelination. However, there was no discrepancy observed between wt and KO mice regarding the capacity of T cells to proliferate or produce IFN-gamma in response to recall Ag. Consequently, we addressed the effect of IFN-beta on encephalitogenic T cell development and the disease initiation phase by passive transfer of autoreactive T cells from KO or wt littermates to both groups of mice. Interestingly, IFN-beta KO mice acquired a higher incidence and augmented EAE regardless of the source of T cells. This shows that the anti-inflammatory effect of endogenous IFN-beta is predominantly exerted on the effector phase of the disease. Histopathological investigations of CNS in the effector phase revealed an extensive microglia activation and TNF-alpha production in IFN-beta KO mice; this was virtually absent in wt littermates. This coincided with an increase in effector functions of T cells in IFN-beta KO mice, as measured by IFN-gamma and IL-4 production. We suggest that lack of endogenous IFN-beta in CNS leads to augmented microglia activation, resulting in a sustained inflammation, cytokine production, and tissue damage with consequent chronic neurological deficits.     

Suppressive DNA vaccination in myelin oligodendrocyte glycoprotein peptide-induced experimental autoimmune encephalomyelitis involves a T1-biased immune response

Vaccination with DNA encoding a myelin basic protein peptide suppresses Lewis rat experimental autoimmune encephalomyelitis (EAE) induced with the same peptide. Additional myelin proteins, such as myelin oligodendrocyte glycoprotein (MOG), may be important in multiple sclerosis. Here we demonstrate that DNA vaccination also suppresses MOG peptide-induced EAE. MOG(91-108) is encephalitogenic in DA rats and MHC-congenic LEW.1AV1 (RT1(av1)) and LEW.1N (RT1(n)) rats. We examined the effects of DNA vaccines encoding MOG(91-108) in tandem, with or without targeting of the hybrid gene product to IgG. In all investigated rat strains DNA vaccination suppressed clinical signs of EAE. There was no requirement for targeting the gene product to IgG, but T1-promoting CpG DNA motifs in the plasmid backbone of the construct were necessary for efficient DNA vaccination, similar to the case in DNA vaccination in myelin basic protein-induced EAE. We failed to detect any effects on ex vivo MOG-peptide-induced IFN-gamma, TNF-alpha, IL-6, IL-4, IL-10, and brain-derived neurotropic factor expression in splenocytes or CNS-derived lymphocytes. In CNS-derived lymphocytes, Fas ligand expression was down-regulated in DNA-vaccinated rats compared with controls. However, MOG-specific IgG2b responses were enhanced after DNA vaccination. The enhanced IgG2b responses together with the requirement for CpG DNA motifs in the vaccine suggest a protective mechanism involving induction of a T1-biased immune response.     

Strong differential regulation of serum and mucosal IgA responses as revealed in CD28-deficient mice using cholera toxin adjuvant

In this study, we show that costimulation required for mucosal IgA responses is strikingly different from that needed for systemic responses, including serum IgA. Following oral immunization with cholera toxin (CT) adjuvant we found that whereas CTLA4-H1 transgenic mice largely failed to respond, CD28-/- mice developed near normal gut mucosal IgA responses but poor serum Ab responses. The local IgA response was functional in that strong antitoxic protection developed in CT-immunized CD28-/- mice. This was in spite of the fact that no germinal centers (GC) were observed in the Peyer's patches, spleen, or other peripheral lymph nodes. Moreover, significant somatic hypermutation was found in isolated IgA plasma cells from gut lamina propria of CD28-/- mice. Thus, differentiation to functional gut mucosal IgA responses against T cell-dependent Ags does not require signaling through CD28 and can be independent of GC formations and isotype-switching in Peyer's patches. By contrast, serum IgA responses, similar to IgG-responses, are dependent on GC and CD28. However, both local and systemic responses are impaired in CTLA4-Hgamma1 transgenic mice, indicating that mucosal IgA responses are dependent on the B7-family ligands, but require signaling via CTLA4 or more likely a third related receptor. Therefore, T-B cell interactions leading to mucosal as opposed to serum IgA responses are uniquely regulated and appear to represent separate events. Although CT is known to strongly up-regulate B7-molecules, we have demonstrated that it acts as a potent mucosal adjuvant in the absence of CD28, suggesting that alternative costimulatory pathways are involved.