Two hybrid transition metal triphosphonates decorated with a tripodal imidazole ligand: synthesis, structures and properties

Two transition-metal triphosphonates with pillar-layered structures were synthesized and characterized. The luminescence, magnetic and proton conductive properties were investigated.

Syntheses and Characterizations of Three Organically Templated Zinc Phosphites with 12-Ring Channels

Three new zinc phosphites, [Hapy]2[Zn3(HPO3)4] (1; apy = 4-aminopyridine), [H2hepip][Zn3(HPO3)4]·(H2O)0.25 (2; hepip = N-(2-hydroxyethyl)piperazine), and [H2tmdab][Zn3(HPO3)4] (3; tmdab = N,N,N′,N′-tetramethyl-1,3-diaminobutane), have been synthesized and characterized by infrared spectroscopy, elemental analysis, thermogravimetric analysis, and powder and single-crystal X-ray diffraction. The frameworks of 1–3 are constructed from 4-connected ZnO4 tetrahedra and 3-connected HPO3 pseudo pyramids with distinct connection mode driven by different organic amine templates. There are 12-membered ring (12-MR) and 8-MR apertures in the (3,4)-connected three-dimensional architecture of 1–3. It is notable that helical chains are observed in the framework of compound 3.

Concise template syntheses of gallium phosphates driven by in situ direct alkylation of aliphatic and aromatic precursors by methanol

In situ template design and generation strategy is applied to synthesize microporous materials. We report five new organically templated gallium phosphates with different structures varying from 1D chain to 2D layer and 3D framework.

An open-framework beryllium phosphite with extra-large 18-ring channels

We report herein a 3D interrupted beryllium phosphite open-framework with a low density (1.594 g cm⁻³), which is the first case of a beryllium phosphite framework containing extra-large 18-ring channels.

Synthesis, Structure, and Characterisation of Two New Open-Framework Zinc Phosphites of Varying Dimensionality

Using homopiperazine (hpip) as a structure directing agent, two new zinc phosphites [H2hpip][Zn2(HPO3)3] (1) and [H2hpip][Zn3(HPO3)4] (2), have been synthesised and structurally characterised by IR spectroscopy, elemental analysis, thermogravimetric analysis, and powder and single-crystal X-ray diffractions. Although both compounds are constructed from the same ZnO4 and HPO3 building units, the final frameworks are distinctly different due to their different connectivity. Compound 1 displays a 2D layered structure with 8-membered ring apertures, while compound 2 possesses a (3,4)-connected 3D architecture with multidirectional intersecting 8- and 12-ring channels. In addition, the simultaneous occurrence of four types of 8-ring channels intersecting the large 12-ring apertures in 2 is unique and observed here for the first time.

The inorganic–organic hybrid zinc phosphite poly[(μ3-hydrogen phosphito-κ3O:O′:O′′)(piperidin-1-ium-4-carboxylate-κO)zinc(II)]

A new inorganic–organic hybrid zinc phosphite, [Zn(HPO3)(C6H11NO2)]n, has been synthesized hydrothermally. Protonated piperidin-1-ium-4-carboxylate (PDCA) was generatedin situby hydrolysis of the piperidine-4-carboxamide precursor. The P atom possesses a typical PO3H pseudo-pyramidal geometry. The crystal structure features an unusual (3,4)-connected two-dimensional inorganic zinc–phosphite layer, with organic PDCA ligands appended to the sheets and protruding into the interlayer region. Helical chains of opposite chirality are involved in the construction of a puckered sheet structure.

Irx4 forms an inhibitory complex with the vitamin D and retinoic X receptors to regulate cardiac chamber-specific slow MyHC3 expression

The slow myosin heavy chain 3 gene (slow MyHC3) is restricted in its expression to the atrial chambers of the heart. Understanding its regulation provides a basis for determination of the mechanisms controlling chamber-specific gene expression in heart development. The observed chamber distribution results from repression of slow MyHC3 gene expression in the ventricles. A binding site, the vitamin D response element (VDRE), for a heterodimer of vitamin D receptor (VDR) and retinoic X receptor alpha (RXR alpha) within the slow MyHC3 promoter mediates chamber-specific expression of the gene. Irx4, an Iroquois family homeobox gene whose expression is restricted to the ventricular chambers at all stages of development, inhibits AMHC1, the chick homolog of quail slow MyHC3, gene expression within developing ventricles. Repression of the slow MyHC3 gene in ventricular cardiomyocytes by Irx4 requires the VDRE. Unlike VDR and RXR alpha, Irx4 does not bind directly to the VDRE. Instead two-hybrid and co-immunoprecipitation assays show that Irx4 interacts with the RXR alpha component of the VDR/RXR alpha heterodimer and that the amino terminus of the Irx4 protein is required for its inhibitory action. These observations indicate that the mechanism of atrial chamber-specific expression requires the formation of an inhibitory protein complex composed of VDR, RXR alpha, and Irx4 that binds at the VDRE inhibiting slow MyHC3 expression in the ventricles.

Cardiomyopathy in Irx4-deficient mice is preceded by abnormal ventricular gene expression

To define the role of Irx4, a member of the Iroquois family of homeobox transcription factors in mammalian heart development and function, we disrupted the murine Irx4 gene. Cardiac morphology in Irx4-deficient mice (designated Irx4(Delta ex2/Delta ex2)) was normal during embryogenesis and in early postnatal life. Adult Irx4(Delta ex2/Delta ex2) mice developed a cardiomyopathy characterized by cardiac hypertrophy and impaired contractile function. Prior to the development of cardiomyopathy, Irx4(Delta ex2/Delta ex2) hearts had abnormal ventricular gene expression: Irx4-deficient embryos exhibited reduced ventricular expression of the basic helix-loop-helix transcription factor eHand (Hand1), increased Irx2 expression, and ventricular induction of an atrial chamber-specific transgene. In neonatal hearts, ventricular expression of atrial natriuretic factor and alpha-skeletal actin was markedly increased. Several weeks subsequent to these changes in embryonic and neonatal gene expression, increased expression of hypertrophic markers BNP and beta-myosin heavy chain accompanied adult-onset cardiac hypertrophy. Cardiac expression of Irx1, Irx2, and Irx5 may partially compensate for loss of Irx4 function. We conclude that Irx4 is not sufficient for ventricular chamber formation but is required for the establishment of some components of a ventricle-specific gene expression program. In the absence of genes under the control of Irx4, ventricular function deteriorates and cardiomyopathy ensues.

Chamber formation and morphogenesis in the developing mammalian heart

In this study we challenge the generally accepted view that cardiac chambers form from an array of segmental primordia arranged along the anteroposterior axis of the linear and looping heart tube. We traced the spatial pattern of expression of genes encoding atrial natriuretic factor, sarcoplasmic reticulum calcium ATPase, Chisel, Irx5, Irx4, myosin light chain 2v, and beta-myosin heavy chain and related these to morphogenesis. Based on the patterns we propose a two-step model for chamber formation in the embryonic heart. First, a linear heart forms, which is composed of "primary" myocardium that nonetheless shows polarity in phenotype and gene expression along its anteroposterior and dorsoventral axes. Second, specialized ventricular chamber myocardium is specified at the ventral surface of the linear heart tube, while distinct left and right atrial myocardium forms more caudally on laterodorsal surfaces. The process of looping aligns these primordial chambers such that they face the outer curvature. Myocardium of the inner curvature, as well as that of inflow tract, atrioventricular canal, and outflow tract, retains the molecular signature originally found in linear heart tube myocardium. Evidence for distinct transcriptional programs which govern compartmentalization in the forming heart is seen in the patterns of expression of Hand1 for the dorsoventral axis, Irx4 and Tbx5 for the anteroposterior axis, and Irx5 for the distinction between primary and chamber myocardium.

rax, Hes1, and notch1 promote the formation of Müller glia by postnatal retinal progenitor cells

We are interested in the mechanisms of glial cell development in the vertebrate central nervous system. We have identified genes that can direct the formation of glia in the retina. rax, a homeobox gene, Hes1, a basic helix-loop-helix gene, and notch1, a transmembrane receptor gene, are expressed in retinal progenitor cells, downregulated in differentiated neurons, and expressed in Müller glia. Retroviral transduction of any of these genes resulted in expression of glial markers. In contrast, misexpression of a dominant-negative Hes1 gene reduced the number of glia. Cotransfection of rax with reporter constructs containing the Hes1 or notch1 regulatory regions led to the upregulation of reporter transcription. These data suggest a regulatory heirarchy that controls the formation of glia at the expense of neurons.

Cardiac expression of the ventricle-specific homeobox gene Irx4 is modulated by Nkx2-5 and dHand

We report the isolation and characterization of the cDNAs encoded by the murine and human homeobox genes, Irx4 (Iroquois homeobox gene 4). Mouse and human Irx4 proteins are highly conserved (83%) and their 63-aa homeodomain is more than 93% identical to that of the Drosophila Iroquois patterning genes. Human IRX4 maps to chromosome 5p15.3, which is syntenic to murine chromosome 13. Irx4 transcripts are present in the developing central nervous system, skin, and vibrissae, but are predominantly expressed in the cardiac ventricles. In mice at embryonic day (E) 7.5, Irx4 transcripts are found in the chorion and at low levels in a discrete anterior domain of the cardiac primordia. During the formation of the linear heart tube and its subsequent looping (E8.0-8.5), Irx4 expression is restricted to the ventricular segment and is absent from both the posterior (eventual atrial) and the anterior (eventual outflow tract) segments of the heart. Throughout all subsequent stages in which the chambers of the heart become morphologically distinct (E8.5-11) and into adulthood, cardiac Irx4 expression is found exclusively in the ventricular myocardium. Irx4 gene expression was also assessed in embryos with aberrant cardiac development: mice lacking RXRalpha or MEF2c have normal Irx4 expression, but mice lacking the homeobox transcription factor Nkx2-5 (Csx) have markedly reduced levels of Irx4 transcripts. dHand-null embryos initiate Irx4 expression, but cannot maintain normal levels. These data indicate that the homeobox gene Irx4 is likely to be an important mediator of ventricular differentiation during cardiac development, which is downstream of Nkx2-5 and dHand.

Regulation of chamber-specific gene expression in the developing heart by Irx4

The vertebrate heart consists of two types of chambers, the atria and the ventricles, which differ in their contractile and electrophysiological properties. Little is known of the molecular mechanisms by which these chambers are specified during embryogenesis. Here a chicken iroquois-related homeobox gene, Irx4, was identified that has a ventricle-restricted expression pattern at all stages of heart development. Irx4 protein was shown to regulate the chamber-specific expression of myosin isoforms by activating the expression of the ventricle myosin heavy chain-1 (VMHC1) and suppressing the expression of the atrial myosin heavy chain-1 (AMHC1) in the ventricles. Thus, Irx4 may play a critical role in establishing chamber-specific gene expression in the developing heart.

The expression and function of Notch pathway genes in the developing rat eye

The Notch gene plays a role in the development of disparate tissues in multiple organisms. Because the vertebrate eye is an excellent model system for both patterning and cell fate determination, two processes that can involve Notch, we examined the expression patterns of Notch 1 and Notch 2, and their ligands Delta and Jagged, in the developing rat eye. Notch 1 and Delta were found to be expressed in the neural retina during the period of cell fate determination and differentiation. Notch 2 was found to be expressed in the non-neuronal derivatives of the optic cup, including the pigment epithelium, optic stalk, and ciliary body. Jagged was expressed in distinct regions within the optic vesicle, ciliary body, and lens, with patterns that changed over time. The potential function of Notch 1 in cell-type specification and differentiation was examined by introducing a constitutively active form of Notch 1 in vivo using a replication-incompetent retrovirus. This form of Notch 1 was found to cause abnormal growth and interfere with the differentiation of multiple retinal cell types.

Alpha 7 beta 1 integrin is a component of the myotendinous junction on skeletal muscle

Immunization against a 70 kDa band that co-purifies with skeletal muscle integrins has resulted in an antibody directed against the avain alpha 7 integrin subunit. The specificity of the antibody was established by patterns of tissue staining and cross-reactivity with antibodies directed against the cytoplasmic domain of the rat alpha 7 cytoplasmic domain. On sections of adult skeletal muscle the alpha 7 integrin was enriched in the myotendinous junction (MTJ). This localization was unique as neither the alpha 1, alpha 3, alpha 5, alpha 6 and alpha v subunit localizes in the myotendinous junction. The distribution of the alpha 7 subunit in the MTJ was examined during embryonic development. alpha 7 expression in the junction is first apparent around embryo day 14 and is almost exclusively at the developing MTJ at this stage. alpha 3 is expressed with distinctive punctate staining around the junctional area in earlier embryos (11-day). The time of appearance of the alpha 7 subunit in the MTJ correlates with the insertion of myofibrils into subsarcolemmal densities and folding of the junctional membrane, suggesting a role of the alpha 7 integrin in this process. Vinculin is present throughout development of the myotendinous junction, suggesting that the alpha 7 integrin recognizes a preformed cytoskeletal structure. The presence of the alpha 7 subunit in the myotendinous junction and the alpha 5 subunit in the adhesion plaque demonstrates a molecular difference between these two adherens junctions. It also points to possible origins of junctional specificity on muscle. Differences between these two junctions were developed further using an antibody against phosphotyrosine (PY20). Phosphotyrosine is thought to participate in the organization and stabilization of adhesions. The focal adhesion and the neuromuscular junction, but not the MTJ, contained proteins phosphorylated on tyrosine.

LBL, a novel, developmentally regulated, laminin-binding lectin

A 190/220-kDa complex found in integrin preparations was purified, and monoclonal antibodies were raised against it. The immunoaffinity-purified complex appears to be a trimer of very similar or identical 70-kDa subunits. It is a novel extracellular matrix molecule as determined by its subunit composition, N-terminal amino acid sequence, and in vivo localization. It is distributed widely in basement membranes including those from muscle, nerve, and kidney. It is also present in connective tissue regions such as perineurium and perimysium. It has the unusual property that it is initially expressed very late in avian development near the time of hatching. This protein is found to copurified with integrin because it binds to the carbohydrate support in Sepharose. Hemagglutination assays with mono- and disaccharides show that it functions as a lectin with galactoside-binding specificity. This protein is also found to bind strongly and specifically to laminin at a site distinct from its lectin activity, but does not bind to fibronectin or type IV collagen. The protein appears to be conserved and is a common contaminant of many laminin preparations. We call this novel protein "LBL" for laminin-binding lectin.

Repression of integrin beta 1 subunit expression by antisense RNA

A quail cell line (QT6-c) was co-transfected with pTEX vector expressing RNA complementary to chicken integrin beta 1 subunit mRNA (Anti-Int) and pRSVneo vector by a calcium phosphate method. Transfectants showing reduced expression of quail integrin beta 1 subunit were selected with an immunoblot assay, and a few positive clones were examined in detail. Northern blot and immunoblot analyses revealed that the Anti-Int caused a clear reduction of the transcript encoding integrin beta 1 subunit depending on culture conditions. The number of cell surface integrins also decreased in proportion to the decrement of the total amount of integrin beta 1 subunits. When one transfectant (QA23) was cultured in a serum-free medium, cell shape changed from fibroblast-like to neuron-like morphology accompanied by a low growth rate, and the cells did not form focal contact on fibronectin. A similar morphological change occurred in QT6-c cells when the cells were infected with Rous Sarcoma virus, which could produce the Anti-Int. The QA23 cells did not attach to fibronectin as efficiently as did the original QT6-c cells. These data suggest that reduced expression of integrin beta 1 subunit affects cell growth as well as cell morphology by disordering the interaction between integrins and matrix proteins and/or cytoplasmic proteins.