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An intergenic region of human chromosome 2 (2p25.3) harbors genetic variants which are among those most strongly and reproducibly associated with obesity. The gene closest to these variants is TMEM18 , although the molecular mechanisms mediating these effects remain entirely unknown. Tmem18 expression in the murine hypothalamic paraventricular nucleus (PVN) was altered by changes in nutritional state. Germline loss of Tmem18 in mice resulted in increased body weight, which was exacerbated by high fat diet and driven by increased food intake. Selective overexpression of Tmem18 in the PVN of wild-type mice reduced food intake and also increased energy expenditure. We provide evidence that TMEM18 has four, not three, transmembrane domains and that it physically interacts with key components of the nuclear pore complex. Our data support the hypothesis that TMEM18 itself, acting within the central nervous system, is a plausible mediator of the impact of adjacent genetic variation on human adiposity., Competing Interests: The authors declare no conflict of interest.

Lipid droplets (LDs) are a conserved feature of most organisms. Vertebrate adipocytes have evolved to efficiently store and release lipids for the whole organism from a single droplet. Perilipin 1, the most abundant lipid-coat protein in adipocytes, plays a key role in regulating lipolysis. In other tissues such as liver and muscle, LDs serve very different biological functions, buffering surplus lipids for subsequent oxidation or export. These tissues express perilipins 2 or 3, rather than perilipin 1. We sought to understand the role of perilipins 2 and 3 in regulating basal lipolysis. Bimolecular fluorescence complementation studies suggested that whereas perilipin 1 prevents the activation of adipose tissue triacylglycerol lipase by its coactivator, AB-hydrolase domain containing-5 (ABHD5), perilipins 2 and 3 do so less effectively. These differences are mediated by a conserved region within the carboxy terminus of perilipin 1 that binds and stabilizes ABHD5 by retarding its degradation by the proteosome. Chimeric proteins generated by fusing the carboxy terminus of perilipin 1 to the amino terminus of perilipins 2 or 3 stabilize ABHD5 and suppress basal lipolysis more effectively than WT perilipins 2 or 3. Furthermore, knockdown of perilipin 1 in adipocytes leads to replacement of perilipin 2 on LDs. In these cells we observed reduced ABHD5 expression and LD localization and a corresponding increase in basal lipolysis. Collectively these data suggest that whereas perilipin 1 potently suppresses basal lipolysis in adipocytes, perilipins 2 and 3 facilitate higher rates of basal lipolysis in other tissues where constitutive traffic of fatty acids via LDs is a necessary step in their metabolism.

Phosphatidylcholine (PC) is the major glycerophospholipid in eukaryotic cells and is an essential component in all cellular membranes. The biochemistry of de novo PC synthesis by the Kennedy pathway is well established, but less is known about the physiological functions of PC. We identified two unrelated patients with defects in the Kennedy pathway due to biallellic loss-of-function mutations in phosphate cytidylyltransferase 1 alpha (PCYT1A), the rate-limiting enzyme in this pathway. The mutations lead to a marked reduction in PCYT1A expression and PC synthesis. The phenotypic consequences include some features, such as severe fatty liver and low HDL cholesterol levels, that are predicted by the results of previously reported liver-specific deletion of murine Pcyt1a. Both patients also had lipodystrophy, severe insulin resistance, and diabetes, providing evidence for an additional and essential role for PCYT1A-generated PC in the normal function of white adipose tissue and insulin action.

The endoplasmic reticulum (ER) stress response detects malfunctions in cellular physiology, and microbial pattern recognition receptors recognize external threats posed by infectious agents. This study has investigated whether proinflammatory cytokine expression by monocyte-derived dendritic cells is affected by the induction of ER stress. Activation of ER stress, in combination with Toll-like receptor (TLR) agonists, markedly enhanced expression of mRNA of the unique p19 subunit of IL-23, and also significantly augmented secretion of IL-23 protein. These effects were not seen for IL-12 secretion. The IL-23 gene was found to be a target of the ER stress-induced transcription factor C/EBP homologous protein (CHOP), which exhibited enhanced binding in the context of both ER stress and TLR stimulation. Knockdown of CHOP in U937 cells significantly reduced the synergistic effects of TLR and ER stress on IL-23p19 expression, but did not affect expression of other LPS-responsive genes. The integration of ER stress signals and the requirement for CHOP in the induction of IL-23 responses was also investigated in a physiological setting: infection of myeloid cells with Chlamydia trachomatis resulted in the expression of CHOP mRNA and induced the binding of CHOP to the IL-23 promoter. Furthermore, knockdown of CHOP significantly reduced the expression of IL-23 in response to this intracellular bacterium. Therefore, the effects of pathogens and other environmental factors on ER stress can profoundly affect the nature of innate and adaptive immune responses.

bir-1, a Caenorhabditis elegans inhibitor-of-apoptosis gene homologous to Survivin is organized in an operon with the transcription cofactor C. elegans SKIP (skp-1). Because genes arranged in operons are frequently linked functionally, we have asked whether BIR-1 also functions in transcription. bir-1 inhibition resulted in multiple developmental defects that overlapped with C. elegans SKIP loss-of-function phenotypes: retention of eggs, dumpy, movement defects, and lethality. bir-1 RNA-mediated interference decreased expression of several gfp transgenes and the endogenous genes dpy-7 and hlh-1. Immunoblot analysis revealed decreased phosphoacetylated histones in bir-1 RNA-mediated interference-treated worms. In a heterologous transfection system, BIR-1 augments thyroid hormone-regulated transcription and has an additive effect with SKIP. These results show that BIR-1 functions in the regulation of transcription and development.

SKI-binding protein (SKIP) is a transcription cofactor present in all eukaryotes. Here we show that SKIP is a unique protein that is required for Caenorhabditis elegans viability and development. Expression of CeSKIP (skp-1) assayed by RT-PCR and by GFP fluorescence in transgenic lines starts in embryos and continues to adulthood. Loss of CeSKIP activity by RNA-mediated inhibition results in early embryonic arrest similar to that seen following inhibition of RNA polymerase II. RNA polymerase II phosphorylation appears normal early in CeSKIP RNA-mediated inhibition treated embryos although the expression of several embryonic GFP reporter genes is severely restricted or absent. Our data suggest that CeSKIP is an essential component of many RNA polymerase II transcription complexes and is indispensable for C. elegans development.