Project description: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. 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. 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.
Project description:The sterol regulatory element binding proteins (SREBPs) are transcription factors that govern cholesterol and fatty acid metabolism. Owing to their central role in controlling hepatic lipid and lipoprotein metabolism their activity is tightly coordinated, and accordingly dysregulation of the SREBP pathway is associated with development of dyslipidemia and non-alcoholic fatty liver disease. Using a suite of genome-wide genetic screens we have recently identified SPRING (C12ORF49) as a novel post-transcriptional regulator of SREBP activation in vitro. Our previous work demonstrated that constitutive ablation of Spring in mice is embryonically lethal. Here we show that inducible global deletion of Spring is also untolerated, and therefore to interrogate the physiological role of SPRING in controlling hepatic lipid metabolism we developed liver-specific Spring knockout mice (LKO). Liver transcriptomics and proteomics analysis revealed severely attenuated SREBP signaling in livers and in hepatocytes of LKO mice, which was associated with marked effects on both plasma and hepatic lipid levels. In plasma, total cholesterol levels were dramatically reduced in both male and female LKO mice, apparent in both the LDL and HDL fractions, while triglyceride levels remained largely unaffected. In liver, loss of Spring diminished cholesterol and triglyceride biosynthesis resulting in decreased hepatic cholesterol and triglyceride content. This coincided with reduced secretion of VLDL into the circulation. Consistent with diminished hepatic de novo lipogenesis, LKO mice were protected from developing hepatosteatosis when challenged with a fructose-rich diet. Supporting the significance of our findings in mice, we identified common and rare SPRING genetic variants that are strongly associated with circulating HDL-c and ApoA1 levels in humans. Collectively, our study positions SPRING as a core component of hepatic SREBP signaling, and consequently of systemic lipid metabolism in mice and humans.
Project description:Marine microalgae (phytoplankton) mediate almost half of the worldwide photosynthetic carbon dioxide fixation and therefore play a pivotal role in global carbon cycling, most prominently during massive phytoplankton blooms. Phytoplankton biomass consists of considerable proportions of polysaccharides, substantial parts of which are rapidly remineralized by heterotrophic bacteria. We analyzed the diversity, activity and functional potential of such polysaccharide-degrading bacteria in different size fractions during a diverse spring phytoplankton bloom at Helgoland Roads (southern North Sea) at high temporal resolution using microscopic, physicochemical, biodiversity, metagenome and metaproteome analyses.