Impacts of Brain Serotonin Deficiency following Tph2 Inactivation on Development and Raphe Neuron Serotonergic Specification

Brain serotonin (5-HT) is implicated in a wide range of functions from basic physiological mechanisms to complex behaviors, including neuropsychiatric conditions, as well as in developmental processes. Increasing evidence links 5-HT signaling alterations during development to emotional dysregulation and psychopathology in adult age. To further analyze the importance of brain 5-HT in somatic and brain development and function, and more specifically differentiation and specification of the serotonergic system itself, we generated a mouse model with brain-specific 5-HT deficiency resulting from a genetically driven constitutive inactivation of neuronal tryptophan hydroxylase-2 (Tph2). Tph2 inactivation (Tph2-/-) resulted in brain 5-HT deficiency leading to growth retardation and persistent leanness, whereas a sex- and age-dependent increase in body weight was observed in Tph2+/- mice. The conserved expression pattern of the 5-HT neuron-specific markers (except Tph2 and 5-HT) demonstrates that brain 5-HT synthesis is not a prerequisite for the proliferation, differentiation and survival of raphe neurons subjected to the developmental program of serotonergic specification. Furthermore, although these neurons are unable to synthesize 5-HT from the precursor tryptophan, they still display electrophysiological properties characteristic of 5-HT neurons. Moreover, 5-HT deficiency induces an up-regulation of 5-HT(1A) and 5-HT(1B) receptors across brain regions as well as a reduction of norepinephrine concentrations accompanied by a reduced number of noradrenergic neurons. Together, our results characterize developmental, neurochemical, neurobiological and electrophysiological consequences of brain-specific 5-HT deficiency, reveal a dual dose-dependent role of 5-HT in body weight regulation and show that differentiation of serotonergic neuron phenotype is independent from endogenous 5-HT synthesis.     

Effect of leaf surface waxes on leaf colonization by Pantoea agglomerans and Clavibacter michiganensis

To evaluate the influence of leaf cuticular waxes on bacterial colonization of leaves, bacterial colonization patterns were examined on four glossy maize (Zea mays L.) mutants that were altered in their cuticular wax biosynthesis. Mutant gl3 was indistinguishable from the wild-type maize in its ability to foster colonization by the two bacterial species, Pantoea agglomerans and Clavibacter michiganensis subsp. nebraskensis. In contrast, the other three mutants supported the development of populations that significantly differed in size from those on the wild type. Mutant gl5 gl20 supported smaller populations of P. agglomerans, but not C. michiganensis, while mutant gl1 supported larger populations of C. michiganensis but not P. agglomerans. Mutant gl4 supported larger populations of both bacterial species. The exceptional ability of mutant gl4 to support bacterial colonization was hypothesized to result from the lower density of the crystalline waxes on gl4 than on the wild type, because a reduced crystal density could promote capillary water movement and water trapping among the wax crystals. This hypothesis was supported by the demonstration that the mechanical introduction of gaps among the wax crystals of the wild-type leaves resulted in the establishment of larger P. agglomerans populations on the altered leaves. These results provide the first direct evidence that leaf surface waxes affect bacterial leaf colonization at various stages of colonization and in a bacterial species-dependent manner.     

Formation of a new receptor-operated channel by heteromeric assembly of TRPP2 and TRPC1 subunits

Although several protein-protein interactions have been reported between transient receptor potential (TRP) channels, they are all known to occur exclusively between members of the same group. The only intergroup interaction described so far is that of TRPP2 and TRPC1; however, the significance of this interaction is unknown. Here, we show that TRPP2 and TRPC1 assemble to form a channel with a unique constellation of new and TRPP2/TRPC1-specific properties. TRPP2/TRPC1 is activated in response to G-protein-coupled receptor activation and shows a pattern of single-channel conductance, amiloride sensitivity and ion permeability distinct from that of TRPP2 or TRPC1 alone. Native TRPP2/TRPC1 activity is shown in kidney cells by complementary gain-of-function and loss-of-function experiments, and its existence under physiological conditions is supported by colocalization at the primary cilium and by co-immunoprecipitation from kidney membranes. Identification of the heteromultimeric TRPP2/TRPC1 channel has implications in mechanosensation and cilium-based Ca(2+) signalling.     

Genetic and environmental contributions to weight, height, and BMI from birth to 19 years of age: an international study of over 12,000 twin pairs

Objective

To examine the genetic and environmental influences on variances in weight, height, and BMI, from birth through 19 years of age, in boys and girls from three continents.

Design and Settings

Cross-sectional twin study. Data obtained from a total of 23 twin birth-cohorts from four countries: Canada, Sweden, Denmark, and Australia. Participants were Monozygotic (MZ) and dizygotic (DZ) (same- and opposite-sex) twin pairs with data available for both height and weight at a given age, from birth through 19 years of age. Approximately 24,036 children were included in the analyses.

Results

Heritability for body weight, height, and BMI was low at birth (between 6.4 and 8.7% for boys, and between 4.8 and 7.9% for girls) but increased over time, accounting for close to half or more of the variance in body weight and BMI after 5 months of age in both sexes. Common environmental influences on all body measures were high at birth (between 74.1–85.9% in all measures for boys, and between 74.2 and 87.3% in all measures for girls) and markedly reduced over time. For body height, the effect of the common environment remained significant for a longer period during early childhood (up through 12 years of age). Sex-limitation of genetic and shared environmental effects was observed.

Conclusion

Genetics appear to play an increasingly important role in explaining the variation in weight, height, and BMI from early childhood to late adolescence, particularly in boys. Common environmental factors exert their strongest and most independent influence specifically in pre-adolescent years and more significantly in girls. These findings emphasize the need to target family and social environmental interventions in early childhood years, especially for females. As gene-environment correlation and interaction is likely, it is also necessary to identify the genetic variants that may predispose individuals to obesity.     

The Cdc48-Ufd1-Npl4 complex is central in ubiquitin-proteasome triggered catabolite degradation of fructose-1,6-bisphosphatase

The switch from gluconeogenesis to glycolysis in yeast has been shown to require ubiquitin-proteasome dependent elimination of the key enzyme fructose-1,6-bisphosphatase (FBPase). Prior to proteasomal degradation, polyubiquitination of the enzyme occurs via the ubiquitin-conjugating enzymes Ubc1, Ubc4, Ubc5 and Ubc8 in conjunction with a novel multi-subunit ubiquitin ligase, the Gid complex. As an additional machinery required for the catabolite degradation process, we identified the trimeric Cdc48^Ufd1-Npl4 complex and the ubiquitin receptors Dsk2 and Rad23. We show that this machinery acts between polyubiquitination of FBPase and its degradation by the proteasome.     

Nuclear Receptor Liver X Receptor Is O-GlcNAc-modified in Response to Glucose

Post-translational modification of nucleocytoplasmic proteins by O-linked β-N-acetylglucosamine (O-GlcNAc) has for the last 25 years emerged as an essential glucose-sensing mechanism. The liver X receptors (LXRs) function as nutritional sensors for cholesterol-regulating lipid metabolism, glucose homeostasis, and inflammation. LXRs are shown to be post-translationally modified by phosphorylation, acetylation, and sumoylation, affecting their target gene specificity, stability, and transactivating and transrepressional activity, respectively. In the present study, we show for the first time that LXRα and LXRβ are targets for glucose-hexosamine-derived O-GlcNAc modification in human Huh7 cells. Furthermore, we observed increased hepatic LXRα O-GlcNAcylation in vivo in refed mice and in streptozotocin-induced refed diabetic mice. Importantly, induction of LXRα O-GlcNAcylation in both mouse models was concomitant with increased expression of the lipogenic gene SREBP-1c (sterol regulatory element-binding protein 1c). Furthermore, glucose increased LXR/retinoic acid receptor-dependent activation of luciferase reporter activity driven by the mouse SREBP-1c promoter via the hexosamine biosynthetic pathway in Huh7 cells. Altogether, our results suggest that O-GlcNAcylation of LXR is a novel mechanism by which LXR acts as a glucose sensor affecting LXR-dependent gene expression, substantiating the crucial role of LXR as a nutritional sensor in lipid and glucose metabolism.     

Genetic uniformity and long‐distance clonal dispersal in the invasive androgenetic Corbicula clams

The clam genus Corbicula is an interesting model system to study the evolution of reproductive modes as it includes both sexual and asexual (androgenetic) lineages. While the sexual populations are restricted to the native Asian areas, the androgenetic lineages are widely distributed being also found in America and Europe where they form a major aquatic invasive pest. We investigated the genetic diversity of native and invasive Corbicula populations through a worldwide sampling. The use of mitochondrial and nuclear (microsatellite) markers revealed an extremely low diversity in the invasive populations with only four, undiversified, genetic lineages distributed across Europe and America. On the contrary, in the native populations, both sexual and androgenetic lineages exhibited much higher genetic diversity. Remarkably, the most abundant and widely distributed invasive forms, the so‐called form A and form R found in America and Europe respectively, are fixed for the same single COI (cytochrome c oxydase subunit I) haplotype and same multilocus genotype. This suggests that form R, observed in Europe since the 1980s, derived directly from form A found in America since the 1920s. In addition, this form shares alleles with some Japanese populations, indicating a Japanese origin for this invasive lineage. Finally, our study suggests that few androgenetic Corbicula individuals successfully invaded the non‐native range and then dispersed clonally. This is one striking case of genetic paradox raising the issue of invasive and evolutionary success of genetically undiversified populations.     

Catalytic activation of human glucokinase by substrate binding: residue contacts involved in the binding of D-glucose to the super-open form and conformational transitions

alpha-D-Glucose activates glucokinase (EC 2.7.1.1) on its binding to the active site by inducing a global hysteretic conformational change. Using intrinsic tryptophan fluorescence as a probe on the alpha-D-glucose induced conformational changes in the pancreatic isoform 1 of human glucokinase, key residues involved in the process were identified by site-directed mutagenesis. Single-site W-->F mutations enabled the assignment of the fluorescence enhancement (DeltaF/F(0)) mainly to W99 and W167 in flexible loop structures, but the biphasic time course of DeltaF/F(0) is variably influenced by all tryptophan residues. The human glucokinase-alpha-D-glucose association (K(d) = 4.8 +/- 0.1 mm at 25 degrees C) is driven by a favourable entropy change (DeltaS = 150 +/- 10 J.mol(-1).K(-1)). Although X-ray crystallographic studies have revealed the alpha-d-glucose binding residues in the closed state, the contact residues that make essential contributions to its binding to the super-open conformation remain unidentified. In the present study, we combined functional mutagenesis with structural dynamic analyses to identify residue contacts involved in the initial binding of alpha-d-glucose and conformational transitions. The mutations N204A, D205A or E256A/K in the L-domain resulted in enzyme forms that did not bind alpha-D-glucose at 200 mm and were essentially catalytically inactive. Our data support a molecular dynamic model in which a concerted binding of alpha-D-glucose to N204, N231 and E256 in the super-open conformation induces local torsional stresses at N204/D205 propagating towards a closed conformation, involving structural changes in the highly flexible interdomain connecting region II (R192-N204), helix 5 (V181-R191), helix 6 (D205-Y215) and the C-terminal helix 17 (R447-K460).