Seasonal Differences of Gene Expression Profiles in Song Sparrow (Melospiza melodia) Hypothalamus in Relation to Territorial Aggression

Background

Male song sparrows (Melospiza melodia) are territorial year-round; however, neuroendocrine responses to simulated territorial intrusion (STI) differ between breeding (spring) and non-breeding seasons (autumn). In spring, exposure to STI leads to increases in luteinizing hormone and testosterone, but not in autumn. These observations suggest that there are fundamental differences in the mechanisms driving neuroendocrine responses to STI between seasons. Microarrays, spotted with EST cDNA clones of zebra finch, were used to explore gene expression profiles in the hypothalamus after territorial aggression in two different seasons.

Methodology/Principal Findings

Free-living territorial male song sparrows were exposed to either conspecific or heterospecific (control) males in an STI in spring and autumn. Behavioral data were recorded, whole hypothalami were collected, and microarray hybridizations were performed. Quantitative PCR was performed for validation. Our results show 262 cDNAs were differentially expressed between spring and autumn in the control birds. There were 173 cDNAs significantly affected by STI in autumn; however, only 67 were significantly affected by STI in spring. There were 88 cDNAs that showed significant interactions in both season and STI.

Conclusions/Significance

Results suggest that STI drives differential genomic responses in the hypothalamus in the spring vs. autumn. The number of cDNAs differentially expressed in relation to season was greater than in relation to social interactions, suggesting major underlying seasonal effects in the hypothalamus which may determine the differential response upon social interaction. Functional pathway analyses implicated genes that regulate thyroid hormone action and neuroplasticity as targets of this neuroendocrine regulation.     

Developmental shifts in gene expression in the auditory forebrain during the sensitive period for song learning

A male zebra finch begins to learn to sing by memorizing a tutor's song during a sensitive period in juvenile development. Tutor song memorization requires molecular signaling within the auditory forebrain. Using microarray and in situ hybridizations, we tested whether the auditory forebrain at an age just before tutoring expresses a different set of genes compared with later life after song learning has ceased. Microarray analysis revealed differences in expression of thousands of genes in the male auditory forebrain at posthatch day 20 (P20) compared with adulthood. Furthermore, song playbacks had essentially no impact on gene expression in P20 auditory forebrain, but altered expression of hundreds of genes in adults. Most genes that were song‐responsive in adults were expressed at constitutively high levels at P20. Using in situ hybridization with a representative sample of 44 probes, we confirmed these effects and found that birds at P20 and P45 were similar in their gene expression patterns. Additionally, eight of the probes showed male–female differences in expression. We conclude that the developing auditory forebrain is in a very different molecular state from the adult, despite its relatively mature gross morphology and electrophysiological responsiveness to song stimuli. Developmental gene expression changes may contribute to fine‐tuning of cellular and molecular properties necessary for song learning. © 2009 Wiley Periodicals, Inc. Develop Neurobiol 2009     

The structures of frataxin oligomers reveal the mechanism for the delivery and detoxification of iron

Defects in the mitochondrial protein frataxin are responsible for Friedreich ataxia, a neurodegenerative and cardiac disease that affects 1:40,000 children. Here, we present the crystal structures of the iron-free and iron-loaded frataxin trimers, and a single-particle electron microscopy reconstruction of a 24 subunit oligomer. The structures reveal fundamental aspects of the frataxin mechanism. The trimer has a central channel in which one atom of iron binds. Two conformations of the channel with different metal-binding affinities suggest that a gating mechanism controls whether the bound iron is delivered to other proteins or transferred to detoxification sites. The trimer constitutes the basic structural unit of the 24 subunit oligomer. The architecture of this oligomer and several features of the trimer structure demonstrate striking similarities to the iron-storage protein ferritin. The data reveal how stepwise assembly provides frataxin with the structural flexibility to perform two functions: metal delivery and detoxification.     

Tumor necrosis factor alpha gene variants do not display allelic imbalance in circulating myeloid cells

Carriage of the TNF −308 A allele (rs1800629 A) has been associated with increased serum TNF-α levels, the development of sepsis syndrome, and fatal outcome, in severely traumatized patients (Menges et al., 2008 [1]). Herein, we analysed the putative allelic imbalance of TNF-α release from myeloid cells. Circulating peripheral blood cells from healthy human blood donors (n = 104) and monocyte-derived macrophages (n = 158) were analysed for their ex vivo capacity of TNF-α expression. Our findings indicate that carriage of the TNF −308 A allele is not associated with high TNF-α expression in circulating human leucocytes and monocyte-derived macrophages. Other cellular sources, e.g. tissue-resident cells like mast cells and/or tissue specific macrophages might be the cellular source of high TNF-α serum levels shortly after trauma.     

Proteomic analysis of common bean seed with storage protein deficiency reveals up-regulation of sulfur-rich proteins and starch and raffinose metabolic enzymes,and down-regulation of the secretory pathway

A deficiency in major seed storage proteins is associated with a nearly two-fold increase in sulfur amino acid content in genetically related lines of common bean (Phaseolus vulgaris). Their mature seed proteome was compared by an approach combining label-free quantification by spectral counting, 2-DE, and analysis of selective extracts. Lack of phaseolin, phytohemagglutinin and arcelin was mainly compensated by increases in legumin, α-amylase inhibitors and mannose lectin FRIL. Along with legumin, albumin-2, defensin and albumin-1 were major contributors to the elevated sulfur amino acid content. Coordinate induction of granule-bound starch synthase I, starch synthase II-2 and starch branching enzyme were associated with minor alteration of starch composition, whereas increased levels of UDP-glucose 4-epimerase were correlated with a 30% increase in raffinose content. Induction of cell division cycle protein 48 and ubiquitin suggested enhanced ER-associated degradation. This was not associated with a classical unfolded protein response as the levels of ER HSC70-cognate binding protein were actually reduced in the mutant. Repression of rab1 GTPase was consistent with decreased traffic through the secretory pathway. Collectively, these results have implications for the nutritional quality of common bean, and provide information on the pleiotropic phenotype associated with storage protein deficiency in a dicotyledonous seed.     

Distribution analysis of hydrogenases in surface waters of marine and freshwater environments

Background

Surface waters of aquatic environments have been shown to both evolve and consume hydrogen and the ocean is estimated to be the principal natural source. In some marine habitats, H₂ evolution and uptake are clearly due to biological activity, while contributions of abiotic sources must be considered in others. Until now the only known biological process involved in H₂ metabolism in marine environments is nitrogen fixation.

Principal Findings

We analyzed marine and freshwater environments for the presence and distribution of genes of all known hydrogenases, the enzymes involved in biological hydrogen turnover. The total genomes and the available marine metagenome datasets were searched for hydrogenase sequences. Furthermore, we isolated DNA from samples from the North Atlantic, Mediterranean Sea, North Sea, Baltic Sea, and two fresh water lakes and amplified and sequenced part of the gene encoding the bidirectional NAD(P)-linked hydrogenase. In 21% of all marine heterotrophic bacterial genomes from surface waters, one or several hydrogenase genes were found, with the membrane-bound H₂ uptake hydrogenase being the most widespread. A clear bias of hydrogenases to environments with terrestrial influence was found. This is exemplified by the cyanobacterial bidirectional NAD(P)-linked hydrogenase that was found in freshwater and coastal areas but not in the open ocean.

Significance

This study shows that hydrogenases are surprisingly abundant in marine environments. Due to its ecological distribution the primary function of the bidirectional NAD(P)-linked hydrogenase seems to be fermentative hydrogen evolution. Moreover, our data suggests that marine surface waters could be an interesting source of oxygen-resistant uptake hydrogenases. The respective genes occur in coastal as well as open ocean habitats and we presume that they are used as additional energy scavenging devices in otherwise nutrient limited environments. The membrane-bound H₂-evolving hydrogenases might be useful as marker for bacteria living inside of marine snow particles.     

T cell responses to allogeneic human mesenchymal stem cells: immunogenicity,tolerance, and suppression

Human mesenchymal stem cells (MSCs) were evaluated for their ability to activate allogeneic T cells in cell mixing experiments. Phenotypic characterization of MSCs by flow cytometry showed expression of MHC Class I alloantigens, but minimal expression of Class II alloantigens and costimulatory molecules, including CD80 (B7-1), CD86 (B7-2), and CD40. T cells purified from peripheral blood mononuclear cells (PBMCs) did not proliferate to allogeneic MSCs. Lack of response was not due to a deficiency of costimulation, since retroviral transduction of MSCs with either B7-1 or B7-2 costimulatory molecules did not result in lymphoproliferation. Although these results suggested that MSCs were immunologically inert or potentially tolerogenic, T cells cultured with MSCs produced IFN- and displayed secondary kinetics to restimulation with PBMCs, indicating alloantigen priming rather than tolerance induction by the MSCs. To determine whether MSCs suppressed alloreactive T cells, MSCs were added to primary mixed lymphocyte reaction (MLR) cultures. MSCs suppressed cell proliferation when added at the initiation of culture or when added to an ongoing MLR culture. Suppression was dose-dependent, genetically unrestricted, and occurred whether or not MSCs were pretreated with IFN-. MSCs in transwell chambers suppressed primary MLR cultures, indicating that suppression was mediated by soluble molecules. Analysis of cytokines in suppressed MLR cultures demonstrated up-regulation of IFN- and IL-10, and down-regulation of TNF- production relative to control cultures. We conclude that MSCs can initiate activation of alloreactive T cells, but do not elicit T cell proliferative responses due to active suppressive mechanisms.