Ankrd17, an ubiquitously expressed ankyrin factor, is essential for the vascular integrity during embryogenesis

Ankyrin repeat domain 17 (Ankrd17) encodes an ubiquitously expressed protein with two clusters of ankyrin repeats. We have used gene targeting strategy to ablate the Ankrd17 gene in mouse. The Ankrd17-deficient mice died between embryonic day (E) 10.5 and E11.5 due to cardiovascular defects. Serious hemorrhages were detected and the vascular smooth muscle cells (vSMCs) surrounding the vessels were drastically reduced in the Ankrd17-deficient embryos, suggesting that the vascular maturation was not completed. Interestingly, vSMC differentiation marker genes were up-regulated in the mutant embryos. Our data have demonstrated the indispensability of Ankrd17 functioning for vascular maturation during early development. The Ankrd17-deficient mice also provide a new animal model for the analysis of the regulatory pathways of the differentiation of vSMC precursor cells.     

Effect of dominant-negative epidermal growth factor receptors on cardiomyocyte hypertrophy

Angiotensin II (AngII) induces heart growth via cardiomyocyte hypertrophy, and central to this is the capacity of the type 1 AngII receptor (AT1R) to "transactivate" epidermal growth factor receptors (EGFRs)--a family with four main subtypes (HER1-4)--although the exact molecular mechanism remains unresolved. In this study, the pharmacological inhibition of AngII-stimulated ERK1/2 activation and cardiomyocyte hypertrophy by increasing concentrations of an EGFR inhibitor, AG1478, indicated that other EGFR subtypes, in addition to HER1, may be involved. We constructed expression vectors and adenoviruses expressing truncated mutant versions of HER1, HER2, and HER4 and determined their capacity to act as dominant-negative inhibitors when co-transfected with full-length EGFRs. It is surprising that adenoviral-mediated expression of these truncated EGFRs in cardiomyocytes led to paradoxical, ligand-independent increases in cardiomyocyte hypertrophy and unusual morphological changes. These results challenge our perception of AT1R-mediated EGFR transactivation and imply that truncated EGFRs may affect cell function through unconventional mechanisms.     

Quantification of bacterial adhesion forces using atomic force microscopy (AFM)

This study demonstrated that atomic force microscopy (AFM) can be used to obtain high-resolution topographical images of bacteria, and to quantify the tip-cell interaction force and the surface elasticity. Results show that the adhesion force between the Si3N4 tip and the bacteria surface was in the range from -3.9 to -4.3 nN. On the other hand, the adhesion forces at the periphery of the cell-substratum contact surface ranged from -5.1 to -5.9 nN and those at the cell-cell interface ranged from -6.5 to -6.8 nN. The two latter forces were considerably greater than the former one, most likely due to the accumulation of extracellular polymer substance (EPS). Results also show that the elasticity varied on the cell surface.     

<Emphasis Type="Italic">Chlorobaculum tepidum</Emphasis> regulates chlorosome structure and function in response to temperature and electron donor availability

Green sulfur bacteria (GSB) rely on the chlorosome, a light-harvesting apparatus comprised almost entirely of self-organizing arrays of bacteriochlorophyll (BChl) molecules, to harvest light energy and pass it to the reaction center. In Chlorobaculum tepidum, over 97% of the total BChl is made up of a mixture of four BChl c homologs in the chlorosome that differ in the number and identity of alkyl side chains attached to the chlorin ring. C. tepidum has been reported to vary the distribution of BChl c homologs with growth light intensity, with the highest degree of BChl c alkylation observed under low-light conditions. Here, we provide evidence that this functional response at the level of the chlorosome can be induced not only by light intensity, but also by temperature and a mutation that prevents phototrophic thiosulfate oxidation. Furthermore, we show that in conjunction with these functional adjustments, the fraction of cellular volume occupied by chlorosomes was altered in response to environmental conditions that perturb the balance between energy absorbed by the light-harvesting apparatus and energy utilized by downstream metabolic reactions.     

Relationship between insertion/deletion (indel) frequency of proteins and essentiality

Background  

In a previous study, we demonstrated that some essential proteins from pathogenic organisms contained sizable insertions/deletions (indels) when aligned to human proteins of high sequence similarity. Such indels may provide sufficient spatial differences between the pathogenic protein and human proteins to allow for selective targeting. In one example, an indel difference was targeted via large scale in-silico screening. This resulted in selective antibodies and small compounds which were capable of binding to the deletion-bearing essential pathogen protein without any cross-reactivity to the highly similar human protein. The objective of the current study was to investigate whether indels were found more frequently in essential than non-essential proteins.     

In Salmonella enterica, the sirtuin-dependent protein acylation/deacylation system (SDPADS) maintains energy homeostasis during growth on low concentrations of acetate

Acetyl-coenzyme A synthetase (Acs) activates acetate into acetyl-coenzyme A (Ac-CoA) in most cells. In Salmonella enterica, acs expression and Acs activity are controlled. It is unclear why the sirtuin-dependent protein acylation/deacylation system (SDPADS) controls the activity of Acs. Here we show that, during growth on 10 mM acetate, acs(+) induction in a S. enterica strain that cannot acetylate (i.e. inactivate) Acs leads to growth arrest, a condition that correlates with a drop in energy charge (0.17) in the acetylation-deficient strain, relative to the energy charge in the acetylation-proficient strain (0.71). Growth arrest was caused by elevated Acs activity, a conclusion supported by the isolation of a single-amino-acid variant (Acs(G266S)), whose overproduction did not arrest growth. Acs-dependent depletion of ATP, coupled with the rise in AMP levels, prevented the synthesis of ADP needed to replenish the pool of ATP. Consistent with this idea, overproduction of ADP-forming Ac-CoA-synthesizing systems did not affect the growth behaviour of acetylation-deficient or acetylation-proficient strains. The Acs(G266S) variant was >2 orders of magnitude less efficient than the Acs(WT) enzyme, but still supported growth on 10 mM acetate. This work provides the first evidence that SDPADS function helps cells maintain energy homeostasis during growth on acetate.     

Effects of increasing doses of glucagon-like peptide-1 on insulin-releasing phases during intravenous glucose administration in mice

The increase in insulin secretion caused by glucagon-like peptide-1 (GLP-1) and GLP-1 mimetics observed during an intravenous glucose test (IVGTT) has been reported in both normal and disease animal models, as well as in humans. In this study, a hierarchical population modeling approach is used, together with a previously reported model relating glucose to insulin appearance, to determine quantitative in vivo dose-response relationships between GLP-1 dose level and both first- and second-phase insulin release. Parameters of the insulin kinetic model were estimated from the complete set of glucose and insulin data collected in 219 anesthetized nonfasted NMR-imaged mice after intravenous injection of glucose (1 g/kg) alone or with GLP-1 (0.03-100 nmol/kg). The resulting dose-response curves indicate a difference in GLP-1 effect on the two release phases, as is also evident from the different ED(50) parameter values (0.107 vs. 6.65 nmol/kg for phase 1 vs. phase 2 insulin release parameters). The first phase of insulin release is gradually augmented with increasing GLP-1 dose, reaching saturation at a dose of ~1 nmol/kg, while the second-phase release changes more abruptly at GLP-1 doses between 3 and 10 nmol/kg and shows a more pronounced 100-fold increase between control and the high GLP-1 dose of 100 nmol/kg Moreover, separate disposition indices calculated for phase 1 and 2 insulin release, show a different pattern of increase with increasing GLP-1 dose.     

Fine mapping of the NRG1 Hirschsprung's disease locus

The primary pathology of Hirschsprung's disease (HSCR, colon aganglionosis) is the absence of ganglia in variable lengths of the hindgut, resulting in functional obstruction. HSCR is attributed to a failure of migration of the enteric ganglion precursors along the developing gut. RET is a key regulator of the development of the enteric nervous system (ENS) and the major HSCR-causing gene. Yet the reduced penetrance of RET DNA HSCR-associated variants together with the phenotypic variability suggest the involvement of additional genes in the disease. Through a genome-wide association study, we uncovered a ～350 kb HSCR-associated region encompassing part of the neuregulin-1 gene (NRG1). To identify the causal NRG1 variants contributing to HSCR, we genotyped 243 SNPs variants on 343 ethnic Chinese HSCR patients and 359 controls. Genotype analysis coupled with imputation narrowed down the HSCR-associated region to 21 kb, with four of the most associated SNPs (rs10088313, rs10094655, rs4624987, and rs3884552) mapping to the NRG1 promoter. We investigated whether there was correlation between the genotype at the rs10088313 locus and the amount of NRG1 expressed in human gut tissues (40 patients and 21 controls) and found differences in expression as a function of genotype. We also found significant differences in NRG1 expression levels between diseased and control individuals bearing the same rs10088313 risk genotype. This indicates that the effects of NRG1 common variants are likely to depend on other alleles or epigenetic factors present in the patients and would account for the variability in the genetic predisposition to HSCR.