SOX10 mutations in chronic intestinal pseudo-obstruction suggest a complex physiopathological mechanism

The type IV Waardenburg syndrome (WS4), also referred to as Shah-Waardenburg syndrome or Waardenburg-Hirschsprung disease, is characterised by the association of Waardenburg features (WS, depigmentation and deafness) and the absence of enteric ganglia in the distal part of the intestine (Hirschsprung disease). Mutations in the EDN3, EDNRB, and SOX10 genes have been reported in this syndrome. Recently, a new SOX10 mutation was observed in a girl with a neural crest disorder without evidence of depigmentation, but with severe constipation due to a chronic intestinal pseudo-obstruction and persistence of enteric ganglia. To refine the nosology of WS, we studied patients with typical WS4 (including Hirschsprung disease) or with WS and intestinal pseudo-obstruction. We found three SOX10 mutations, one EDNRB and one EDN3 mutations in patients presenting with the classical form of WS4, and two SOX10 mutations in patients displaying chronic intestinal pseudo-obstruction and WS features. These results show that chronic intestinal pseudo-obstruction may be a manifestation associated with WS, and indicate that aganglionosis is not the only mechanism underlying the intestinal dysfunction of patients with SOX10 mutations.     

The adrenomedullin receptor acts as clearance receptor in pulmonary circulation

Adrenomedullin (AM) is a powerful pulmonary vasodilator with antimitogenic properties. We investigated the role of the AM receptor (AMR) and the calcitonin gene-related peptide type-1 receptor (CGRP1R) in regulating pulmonary vascular AM levels. The AMR antagonist hAM(22-52) (120 nmol/L) significantly elevated AM release compared with controls to 250% after 2 h in isolated rat lungs and to 830% after 4 h in pulmonary artery endothelial cells (PAEC). CGRP1R blockade had no effect. AMR blockade did not influence prepro-AM mRNA levels nor did inhibition of protein synthesis by cycloheximide (0.01 mg/mL) abolish the effect of the AMR antagonist. Radioligand-binding studies with PAEC membranes revealed a decrease by 44% of the AMR density in response to AMR antagonism. Altogether, the pulmonary vascular AMR represents not only a functionally active, but also a clearance receptor; its expression is constitutively stimulated by basal AM. This identifies a novel mechanism for controlling pulmonary AM levels.     

Forced subunit assembly in alpha1beta2gamma2 GABAA receptors. Insight into the absolute arrangement

The major isoform of the gamma-aminobutyric acid type A (GABA(A)) receptor is thought to be composed of 2alpha(1), 2beta(2), and 1gamma(2) subunit(s), which surround the ion pore. Definite evidence for the subunit arrangement is lacking. We show here that GABA(A) receptor subunits can be concatenated to a trimer that can be functionally expressed upon combination with a dimer. Many combinations did not result in the functional expression. In contrast, four different combinations of triple subunits with dual subunit constructs, all resulting in the identical pentameric receptor gamma(2)beta(2)alpha(1)beta(2)alpha(1), could be successfully expressed in Xenopus oocytes. We characterized the functional properties of these receptors in respect to agonist, competitive antagonist, and diazepam sensitivity. All properties were similar to those of wild type alpha(1)beta(2)gamma(2) GABA(A) receptors. Thus, together with information on the crystal structure of the homologous acetylcholine-binding protein (Brejc, K., van Dijk, W. J., Klaassen, R. V., Schuurmans, M., van Der Oost, J., Smit, A. B., and Sixma, T. K., (2001) Nature 411, 269-276, we provide evidence for an arrangement gamma(2)beta(2)alpha(1)beta(2)alpha(1), counterclockwise when viewed from the synaptic cleft. Forced subunit assembly will also allow receptors containing different subunit isoforms or mutant subunits to be expressed, each in a desired position. The methods established here should be applicable to the entire ion channel family comprising nicotinic acetylcholine, glycine, and 5HT(3) receptors.     

Myostatin expression in age and denervation-induced skeletal muscle atrophy

Myostatin is hypothesized to regulate skeletal muscle mass and to be a potential target for therapeutic intervention in sarcopenia. To clarify whether myostatin is invariably associated with sarcopenia, this study examined the levels of expression of myostatin mRNA and protein in Sprague Dawley rats during aging- and denervation-induced sarcopenia. The level of myostatin mRNA in the gastrocnemius decreased progressively with age being 9, 34 and 56% lower at 6, 12 and 27 months, respectively, compared with mRNA levels at 1.5 months. In contrast, two low molecular mass isoforms of myostatin protein identified by Western blotting increased progressively with age. With denervation, myostatin mRNA was 31% higher on day 1 but by 14 days after sciatic neurectomy when the muscle had atrophied 50%, myostatin expression decreased 34% relative to the sham operated limb. Western analysis of the denervated gastrocnemius showed that myostatin protein levels varied in parallel with mRNA. These disparate patterns of expression of myostatin during age- and denervation-induced atrophy suggest that the regulation of myostatin is complex and variable depending on whether the atrophy is slowly or rapidly progressive.     

Cellular lipid dynamics

During the past years, the notion of microdomains at the surface of cellular membranes has been developed. These are constituted by lipid rafts which involve sphingoglycolipids and cholesterol. To these rafts are associated proteins which have a lipid anchor or are transmembrane proteins. These lipid rafts target specific proteins at the plasma membrane surface and can remain associated with them. They are present in surface receptors and endocytosis occurs upon binding of the specific ligands. Thus these rafts participate to major aspects of cellular dynamics. These rafts are complex structures, insoluble in non-ionic detergents. According to the detergent used, many types of rafts can be isolated. Any alteration of cholesterol, sphingoglycolipids, or abnormalities of the proteins themselves, can lead to abnormal targeting at the membrane surface. It is possible that specific sphingoglycolipids are necessary to target specific proteins at the membrane surface. This may explain the complexity of the sphingoglycolipid molecules, both in relation to their oligosaccharide and to their ceramide structures. There is both a cellular and a tissue specificity of these constituents. Complex sphingoglycolipids are involved in cellular differentiation, cellular polarization, and modified in relation to cancer. Virus and bacteria can be linked to the sphingoglycolipids of these microdomains and alter cellular signaling and function. Sphingoglycolipids are involved in autoimmune diseases as antibody targets and in neurolipidoses which are genetic diseases involving their catabolism. The dynamics of the lipid rafts, in relation to cholesterol, can be altered in Niemann-Pick's disease type C and in Alzheimer's disease. Thus these microdomains are involved in many aspects related to normal and pathological cellular dynamics.     

Homothorax switches function of Drosophila photoreceptors from color to polarized light sensors

Different classes of photoreceptors (PRs) allow animals to perceive various types of visual information. In the Drosophila eye, the outer PRs of each ommatidium are involved in motion detection while the inner PRs mediate color vision. In addition, flies use a specialized class of inner PRs in the "dorsal rim area" of the eye (DRA) to detect the e-vector of polarized light, allowing them to exploit skylight polarization for orientation. We show that homothorax is both necessary and sufficient for inner PRs to adopt the polarization-sensitive DRA fate instead of the color-sensitive default state. Homothorax increases rhabdomere size and uncouples R7-R8 communication to allow both cells to express the same opsin rather than different ones as required for color vision. Homothorax expression is induced by the iroquois complex and the wingless (wg) pathway. However, crucial wg pathway components are not required, suggesting that additional signals are involved.     

Taurocholate feeding prevents CCl4-induced damage of large cholangiocytes through PI3-kinase-dependent mechanism

Bile acids are cytoprotective in hepatocytes by activating phosphatidylinositol-3-kinase (PI3-K) and its downstream signal AKT. Our aim was to determine whether feeding taurocholate to CCl(4)-treated rats reduces cholangiocyte apoptosis and whether this cytoprotective effect is dependent on PI3-K. Cholangiocyte proliferation, secretion, and apoptosis were determined in cholangiocytes from bile duct ligation (BDL), CCl(4)-treated BDL rats, and CCl(4)-treated taurocholate-fed rats. In vitro, we tested whether CCl(4) induces apoptosis and whether loss of cholangiocyte proliferation and secretion is dependent on PI3-K. The CCl(4)-induced cholangiocyte apoptosis and loss of cholangiocyte proliferation and secretion were reduced in CCl(4)-treated rats fed taurocholate. CCl(4)-induced cholangiocyte apoptosis, loss of cholangiocytes secretion, and proliferation were prevented by preincubation with taurocholate. Taurocholate cytoprotective effects were ablated by wortmannin. Taurocholate prevented, in vitro, CCl(4)-induced decrease of phosphorylated AKT protein expression in cholangiocytes. The cytoprotective effects of taurocholate on CCl(4) effects on cholangiocyte proliferation and secretion were abolished by wortmannin. Taurocholate protects cholangiocytes from CCl(4)-induced apoptosis by a PI3-K-dependent mechanism. Bile acids are important in the prevention of drug-induced ductopenia in cholangiopathies.     

Expression of α1-adrenergic receptor subtypes in heart cell culture

Three ₁AR subtypes have been cloned so far and are designated as _1a, _1b, and _1d. Organspecific distribution pattern and subtype-specific effects are known but not fully understood. To address a cell-type specific expression pattern in the heart we investigated expression pattern of ₁AR subtypes on RNA and proteinlevel in heart tissue, cultured cardiomyocytes and nonmyocytes of the rat. Each ₁ARsubtype mRNA was present in neonatal and adult rat heart culture but the relative distribution pattern was significantly different. While the _1aAR subtype is preferentially expressed in adult cardiomyocytes, the _1bAR subtype was preferentially expressed in the nonmyocyte cell fraction. The RTPCR results were confirmed by Westernblotting (_1b) and immunocytochemical studies. Incubation with an ₁agonist (phenylephrine) for 72 h led to a significant reduction of the _1bAR in neonatal heart cell culture on both mRNA and protein level. In contrast, incubation with an ₁antagonist (prazosin) induced a 1.6 fold upregulation of the _1aAR mRNA without significant effects on radioligand binding and functional assay. The results indicate a distribution pattern of the ₁AR subtype which is specific for cell type and ontogeny of the rat heart and may be regulated by adrenergic agents.     

The Epstein-Barr virus lytic program is controlled by the co-operative functions of two transactivators

The propagation of herpesviruses has long been viewed as a temporally regulated sequential process that results from the consecutive expression of specific viral transactivators. As a key step in this process, lytic viral DNA replication is considered as a checkpoint that controls the expression of the late structural viral genes. In a novel genetic approach, we show that both hypotheses do not hold true for the Epstein-Barr virus (EBV). The study of viral mutants of EBV in which the early genes BZLF1 and BRLF1 are deleted allowed a precise assignment of the function of these proteins. Both transactivators were absolutely essential for viral DNA replication. Both BZLF1 and BRLF1 were required for full expression of the EBV proteins expressed during the lytic program, although the respective influence of these molecules on the expression of various viral target genes varied greatly. In replication-defective viral mutants, neither early gene expression nor DNA replication was a prerequisite for late gene expression. This work shows that BRLF1 and BZLF1 harbor distinct but complementary functions that influence all stages of viral production.