Polycomb comes of age: genome-wide profiling of target sites

The Polycomb group proteins are best known for their role as epigenetic regulators of the fly homeotic (Hox) gene clusters, but it has long been clear that these well conserved proteins have many other targets. For example, they are vital for maintaining both the pluripotency of stem cells and the identity of differentiated cells. However, a comprehensive list of experimentally defined targets has been lacking. Six new studies use genome wide profiling techniques to map Polycomb targets in stem cells and differentiated cells in vertebrates and flies. The findings of these studies demand that we rethink some of our current assumptions about Polycomb function.     

Purification and characterization of recombinant ligand-binding domains from the ecdysone receptors of four pest insects

Cloned EcR and USP cDNAs encoding the ecdysone receptors of four insect pests (Lucilia cuprina, Myzus persicae, Bemisia tabaci, Helicoverpa armigera) were manipulated to allow the co-expression of their ligand binding domains (LBDs) in insect cells using a baculovirus vector. Recombinant DE/F segment pairs (and additionally, for H. armigera, an E/F segment pair) from the EcR and USP proteins associated spontaneously with high affinity to form heterodimers that avidly bound an ecdysteroid ligand. This shows that neither ligand nor D-regions are essential for the formation of tightly associated and functional LBD heterodimers. Expression levels ranged up to 16.6mg of functional apo-LBD (i.e., unliganded LBD) heterodimer per liter of recombinant insect cell culture. Each recombinant heterodimer was affinity-purified via an oligo-histidine tag at the N-terminus of the EcR subunit, and could be purified further by ion exchange and/or gel filtration chromatography. The apo-LBD heterodimers appeared to be more easily inactivated than their ligand-containing counterparts: after purification, populations of the former were <40% active, whereas for the latter >70% could be obtained as the ligand-LBD heterodimer complex. Interestingly, we found that the amount of ligand bound by recombinant LBD heterodimer preparations could be enhanced by the non-denaturing detergent CHAPS (3-[(3-cholamidopropyl)dimethyl-ammonio]-1-propanesulfonate). Purity, integrity, size and charge data are reported for the recombinant proteins under native and denaturing conditions. Certain intra- and intermolecular disulfide bonds were observed to form in the absence of reducing agents, and thiol-specific alkylation was shown to suppress this phenomenon but to introduce microheterogeneity.     

Optimization of neuropeptide extraction from the mouse hypothalamus

Sample preparation for neuropeptidomic studies is a critical issue since protein degradation can produce high levels of peptides that obscure the endogenous neuropeptides. We compared different extraction conditions for the recovery of neuropeptides and the formation of protein breakdown fragments from mouse hypothalami. Sonication and heating in water (70 degrees C for 20 min) followed by cold acid and centrifugation enabled the efficient extraction of many neuropeptides without the formation of protein degradation fragments seen with hot acid extractions. The hot water/cold acid extraction procedure resulted in the reproducible recovery of many hypothalamic peptides, including several novel peptides.     

Synthesis and preliminary evaluation of radiolabeled bis(zinc(II)-dipicolylamine) coordination complexes as cell death imaging agents

The aim of this study was the development of (??m)Tc labeled bis(zinc(II)-dipicolylamine) (Zn2?-DPA) coordination complexes, and the in vivo evaluation of their usefulness as radiotracers for the detection of cell death. DPA ligand 1 was labeled with (??m)Tc via the (??m)Tc-tricarbonyl core ([(??m)Tc(CO)?-1]3?) or via HYNIC ((??m)Tc-HYNIC-1) in good radiochemical yields. Highest in vitro stabilities were demonstrated for [(??m)Tc(CO)?-1]3?. A mouse model of hepatic apoptosis (anti-Fas mAb) was used to demonstrate binding to apoptotic cells. (??m)Tc-HYNIC-1 showed the best targeting of apoptotic hepatic tissue with a 2.2 times higher liver uptake in anti-Fas treated mice as compared to healthy animals. A rat model of ischemia-reperfusion injury was used to further explore the ability of the (??m)Tc-labeled Zn2?-DPA coordination complexes to target cell death. Selective accumulation could be detected for both tracers in the area at risk, correlating with histological proof of cell death. Area at risk to normal tissue uptake ratios were 3.82 for [(??m)Tc(CO)?-1]3? and 5.45 for (??m)Tc-HYNIC-1.     

Highly pathogenic avian influenza virus H5N1 infects alveolar macrophages without virus production or excessive TNF-alpha induction

Highly pathogenic avian influenza virus (HPAIV) of the subtype H5N1 causes severe, often fatal pneumonia in humans. The pathogenesis of HPAIV H5N1 infection is not completely understood, although the alveolar macrophage (AM) is thought to play an important role. HPAIV H5N1 infection of macrophages cultured from monocytes leads to high percentages of infection accompanied by virus production and an excessive pro-inflammatory immune response. However, macrophages cultured from monocytes are different from AM, both in phenotype and in response to seasonal influenza virus infection. Consequently, it remains unclear whether the results of studies with macrophages cultured from monocytes are valid for AM. Therefore we infected AM and for comparison macrophages cultured from monocytes with seasonal H3N2 virus, HPAIV H5N1 or pandemic H1N1 virus, and determined the percentage of cells infected, virus production and induction of TNF-alpha, a pro-inflammatory cytokine. In vitro HPAIV H5N1 infection of AM compared to that of macrophages cultured from monocytes resulted in a lower percentage of infected cells (up to 25% vs up to 84%), lower virus production and lower TNF-alpha induction. In vitro infection of AM with H3N2 or H1N1 virus resulted in even lower percentages of infected cells (up to 7%) than with HPAIV H5N1, while virus production and TNF-alpha induction were comparable. In conclusion, this study reveals that macrophages cultured from monocytes are not a good model to study the interaction between AM and these influenza virus strains. Furthermore, the interaction between HPAIV H5N1 and AM could contribute to the pathogenicity of this virus in humans, due to the relative high percentage of infected cells rather than virus production or an excessive TNF-alpha induction.     

Hostile takeover by Plasmodium: reorganization of parasite and host cell membranes during liver stage egress

The protozoan parasite Plasmodium is transmitted by female Anopheles mosquitoes and undergoes obligatory development within a parasitophorous vacuole in hepatocytes before it is released into the bloodstream. The transition to the blood stage was previously shown to involve the packaging of exoerythrocytic merozoites into membrane-surrounded vesicles, called merosomes, which are delivered directly into liver sinusoids. However, it was unclear whether the membrane of these merosomes was derived from the parasite membrane, the parasitophorous vacuole membrane or the host cell membrane. This knowledge is required to determine how phagocytes will be directed against merosomes. Here, we fluorescently label the candidate membranes and use live cell imaging to show that the merosome membrane derives from the host cell membrane. We also demonstrate that proteins in the host cell membrane are lost during merozoite liberation from the parasitophorous vacuole. Immediately after the breakdown of the parasitophorous vacuole membrane, the host cell mitochondria begin to degenerate and protein biosynthesis arrests. The intact host cell plasma membrane surrounding merosomes allows Plasmodium to mask itself from the host immune system and bypass the numerous Kupffer cells on its way into the bloodstream. This represents an effective strategy for evading host defenses before establishing a blood stage infection.     

Trans fat diet causes decreased brood size and shortened lifespan in Caenorhabditis elegans delta-6-desaturase mutant fat-3

Trans-fatty acids (TFAs) enter the diet through industrial processes and can cause adverse human health effects. The present study was aimed to examine the effects of dietary cis- and trans-fatty acids on the model organism Caenorhabditis elegans. Cis- or trans-18:1n9 triglycerides (25 μM) caused no apparent changes in the numbers of viable progeny of wild-type N2 animals. However, in fat-3 mutants lacking delta-6-desaturase, the trans-isomer caused modest decreases in lifespan and progeny after three generations. Long-chain polyunsaturated fatty acids (PUFA) profiles were significantly altered in fat-3 mutants compared to wild type but were not altered after exposure to dietary cis- or trans-18:1n9. Genome-wide expression analysis of fat-3 mutants revealed hundreds of changes. Several genes involved in fat metabolism (acs-2, fat-7, mdt-15) were significantly increased by cis- or trans-18:1n9 without discrimination between isomers. These results provide support for the hypothesis that dietary trans fats are detrimental to development and aging.