Zur Beziehung zwischen endogener Atmung und Glucoseatmung bei Chlorella.

Zusammenfassung Mit Hilfe von Chlorellakulturen, deren Zellmaterial durch autotrophe Anzucht in C¹³-reichem CO₂ markiert war, wurde nachgewiesen, daß die Veratmung von endogenem Substrat bei Zufuhr von Glucose nicht unterdrückt wird. Die endogene Atmung ist vielmehr in Gegenwart von Glucose merklich gesteigert.     

Altered White Matter Architecture in BDNF Met Carriers

Brain-derived neurotrophic factor (BDNF) modulates the pruning of synaptically silent axonal arbors. The Met allele of the BDNF gene is associated with a reduction in the neurotrophin''s activity-dependent release. We used diffusion-weighted imaging to construct structural brain networks for 36 healthy subjects with known BDNF genotypes. Through permutation testing we discovered clear differences in connection strength between subjects carrying the Met allele and those homozygotic for the Val allele. We trained a Gaussian process classifier capable of identifying the subjects'' allelic group with 86% accuracy and high predictive value. In Met carriers structural connectivity was greatly increased throughout the forebrain, particularly in connections corresponding to the anterior and superior corona radiata as well as corticothalamic and corticospinal projections from the sensorimotor, premotor, and prefrontal portions of the internal capsule. Interhemispheric connectivity was also increased via the corpus callosum and anterior commissure, and extremely high connectivity values were found between inferior medial frontal polar regions via the anterior forceps. We propose that the decreased availability of BDNF leads to deficits in axonal maintenance in carriers of the Met allele, and that this produces mesoscale changes in white matter architecture.     

The c-Cbl-associated protein and c-Cbl are two new partners of the SH2-containing inositol polyphosphate 5-phosphatase SHIP2

SHIP2 is a phosphatidylinositol 3,4,5-trisphosphate (PtdIns(3,4,5)P(3)) 5-phosphatase which contains motifs susceptible to mediate protein-protein interaction. Using yeast two-hybrid, GST-pulldown, and coimmunoprecipitation studies, we isolated the CAP cDNA as a specific partner of SHIP2 proline-rich domain and showed by GST-pulldown experiments that the interaction took place with the SH3C of CAP. The interaction was not modulated in COS-7 cells stimulated by EGF neither in CHO cells overexpressing the insulin receptor in the presence or absence of insulin stimulation. We also showed that SHIP2 was able to coimmunoprecipitate with endogenous c-Cbl protein in the absence of CAP and with the insulin receptor in CHO-IR cell extracts. The presence of SHIP2 in a complex around the insulin receptor could account for the very specific increase in insulin sensitivity of SHIP2 knock-out mice.     

Quaking is essential for blood vessel development

For nearly 40 years functional studies of the mouse quaking gene (qkI) have focused on its role in the postnatal central nervous system during myelination. However, the homozygous lethality of a number of ENU-induced alleles reveals that quaking has a critical role in embryonic development prior to the start of myelination. In this article, we show that quaking has a previously unsuspected and essential role in blood vessel development. Interestingly, we found that quaking, a nonsecreted protein, is expressed in the yolk sac endoderm, adjacent to the mesodermal site of developing blood islands, where the differentiation of blood and endothelial cells first occurs. Antibodies against PE-CAM-1, TIE-2 and SM-alpha-actin reveal that embryos homozygous for the qk(k2) allele have defective yolk sac vascular remodeling and abnormal vessels in the embryo proper at midgestation, coinciding with the timing of embryonic death. However, these mutants exhibit normal expression of Nkx2.5 and alpha-sarcomeric actin, indicating that cardiac muscle differentiation was normal. Further, they had normal embryonic heart rates in culture, suggesting that cardiac function was not compromised at this stage of embryonic development. Together, these results suggest that quaking plays an essential role in vascular development and that the blood vessel defects are the cause of embryonic death.     

Progressive Myoclonic Epilepsy-Associated Gene KCTD7 is a Regulator of Potassium Conductance in Neurons

The potassium channel tetramerization domain-containing protein 7 (KCTD7) was named after the structural homology of its predicted N-terminal broad complex, tramtrack and bric à brac/poxvirus and zinc finger domain with the T1 domain of the Kv potassium channel, but its expression profile and cellular function are still largely unknown. We have recently reported a homozygous nonsense mutation of KCTD7 in patients with a novel form of autosomal recessive progressive myoclonic epilepsy. Here, we show that KCTD7 expression hyperpolarizes the cell membrane and reduces the excitability of transfected neurons in patch clamp experiments. We found the expression of KCTD7 in the hippocampal and Purkinje cells of the murine brain, an expression profile consistent with our patients’ phenotype. The effect on the plasma membrane resting potential is possibly mediated by Cullin-3, as we demonstrated direct molecular interaction of KCTD7 with Cullin-3 in co-immunoprecipitation assays. Our data link progressive myoclonic epilepsy to an inherited defect of the neuron plasma membrane’s resting potential in the brain.     

SHIP2 interaction with the cytoskeletal protein Vinexin

The src homology 2 (SH2) domain-containing inositol 5-phosphatase 2 (SHIP2) catalyses the dephosphorylation of phosphatidylinositol 3,4,5-trisphosphate [PtdIns(3,4,5)P3] to phosphatidylinositol 3,4-bisphosphate [PtdIns(3,4)P2]. We report the identification of the cytoskeletal protein Vinexin as a protein interacting with SHIP2. This was achieved by yeast two-hybrid screening using the C-terminal region of SHIP2 as bait. Vinexin has previously been identified as a vinculin-binding protein that plays a key role in cell spreading and cytoskeletal organization. The interaction between SHIP2 and Vinexin was confirmed in lysates of both COS-7 cells and mouse embryonic fibroblasts (MEF). The C-terminus was involved in the interaction, as shown by the transfection of a truncated C-terminus mutant of SHIP2. In addition, we showed the colocalization between Vinexin alpha and SHIP2 at the periphery of transfected COS-7 cells. When added in vitro to SHIP2, Vinexin did not affect the PtdIns(3,4,5)P3 5-phosphatase activity of SHIP2. Enhanced cell adhesion to collagen-I-coated dishes was shown upon transfection of either SHIP2 or Vinexin to COS-7 cells. This effect was no longer observed with either a catalytic mutant or the C-terminus mutant of SHIP2. It also appears SHIP2 specific; this was not seen with SHIP1. Adhesion to the same matrix was decreased in SHIP2-/- MEF cells compared with MEF+/+ cells. Our data suggest that SHIP2 interaction with Vinexin promotes the localization of SHIP2 at the periphery of the cells leaving its catalytic site intact. The complex formation between Vinexin and SHIP2 may increase cellular adhesion. The data reinforce the concept that SHIP2 is active both as a PtdIns(3,4,5)P3 5-phosphatase and as a modulator of focal contact formation.     

Deleterious mutations in LRBA are associated with a syndrome of immune deficiency and autoimmunity

Most autosomal genetic causes of childhood-onset hypogammaglobulinemia are currently not well understood. Most affected individuals are simplex cases, but both autosomal-dominant and autosomal-recessive inheritance have been described. We performed genetic linkage analysis in consanguineous families affected by hypogammaglobulinemia. Four consanguineous families with childhood-onset humoral immune deficiency and features of autoimmunity shared genotype evidence for a linkage interval on chromosome 4q. Sequencing of positional candidate genes revealed that in each family, affected individuals had a distinct homozygous mutation in LRBA (lipopolysaccharide responsive beige-like anchor protein). All LRBA mutations segregated with the disease because homozygous individuals showed hypogammaglobulinemia and autoimmunity, whereas heterozygous individuals were healthy. These mutations were absent in healthy controls. Individuals with homozygous LRBA mutations had no LRBA, had disturbed B cell development, defective in vitro B cell activation, plasmablast formation, and immunoglobulin secretion, and had low proliferative responses. We conclude that mutations in LRBA cause an immune deficiency characterized by defects in B cell activation and autophagy and by susceptibility to apoptosis, all of which are associated with a clinical phenotype of hypogammaglobulinemia and autoimmunity.