PubMed Health⌕ Search

Biomedical subjects

Michael C Holmes

Publications and source records attributed to Michael C Holmes.

8 recordsLinked to original sources
PubMed2006

Mesh phases in a ternary nonionic surfactant, oil, and water system.

The binary system of hexaethylene glycol n-hexadecyl ether (C16EO6) and water (2H2O) has a complex, temperature-dependent lyotropic phase sequence, in the concentration region of 48-62 wt %. On cooling it shows the sequence lamellar phase, L(alpha), random mesh phase Mh1(0), rhombohedral mesh phase, Mh1(R(-)3m), bicontinuous cubic phase, V1(Ia(-)3d), and a two-phase hexagonal region, H1+Lbeta. On heating from the latter two-phase region the phase sequence is V1(Ia(-)3d), ,Mh1(0), and Lalpha. Polarizing optical microscopy, 2H nuclear magnetic resonance, and small-angle X-ray scattering have been used to study the stability of these phases, their sequence, and their physical parameters with the addition of the oils, 1-hexene, decane, and octadecane. The oils are located within the alkyl chain regions of the mesophase structures. Depending on whether the added oil is "penetrating" or "swelling", it may reside in the region between the C16 alkyl chains of the surfactant or at the center of the bilayer and affect phase stability. Oils affect both the volume of the alkyl chain region (at fixed surfactant water mole ratio) and the rigidity of the interfacial region. Both effects can influence the phase structures and their ranges of stability. Adding different types of oil to the mesh phases gives an opportunity to understand the factors that are important in their formation. The transition from the Mh1(R(-)3m) phase to Mh1(0) phase is triggered by the hydrocarbon region swelling to a critical volume fraction of 0.32, a surfactant rod radius of approximately 1.75 nm, and a critical water layer thickness of approximately 2.5 nm. The latter is most likely responsible for a weakening of the interlayer headgroup overlap interaction and the loss of correlation between the layers. The lamellar phase becomes the only stable phase at high oil content.

Journal Article↗
PubMed2006

Controlling gene expression in Drosophila using engineered zinc finger protein transcription factors.

Zinc finger protein transcription factors (ZFP TFs) have been designed to control the expression of endogenous genes in a variety of cells. However, thus far the use of engineered ZFP TFs in germline transgenic settings has been restricted to plants. Here we report that ZFP TFs can regulate gene expression in transgenic Drosophila. To demonstrate this, we targeted the promoter of the well-characterized fushi tarazu (ftz) gene with a ZFP TF activator using the VP16 activation domain from Herpes simplex virus, and ZFP TF repressors using the Drosophila methyl-CpG binding domain (MBD)-like Delta protein. Heat-shock-inducible expression of the ZFP TF activator and repressors resulted in reciprocal effects on ftz regulation, as deduced from changes in the staining pattern and intensity of ftz and en gene expression, and from the cuticular analysis of first instar larvae. These data demonstrate the utility of ZFP TFs as tools for controlling gene expression in the context of a metazoan organism.

Animals↗
PubMed2006

2H NMR evidence for the formation of random mesh phases in nonionic surfactant-water systems.

Random mesh phases share many common features with the classical lamellar phase in that they are layered phases; but crucially, they possess nonuniform interfacial curvature, since the lamellae are pierced by water-filled pores. The introduction of curvature into the lamellae has been posited as a transitional precursor for other lyotropic phases. In this paper, we show that simple 2H nuclear magnetic resonance (NMR) experiments provide strong indication for the formation of the random mesh phase and the NMR data correlate well with literature results from small-angle X-ray scattering. The thermal evolution of the recorded quadrupolar splitting (DeltanuQ) is monitored within the lamellar phase of two nonionic surfactants, C16E6 and C12E5, as the samples are cooled or heated, and a marked and reversible change in the evolution of DeltanuQ is observed. Data from heavy water and deuterium labeled surfactant show the same temperature dependence and consequently report on the same structural changes with temperature. The formation of the random mesh phase is quantified in terms of an effective order parameter that is unity in the classical lamellar phase and takes values of <1 in the random mesh phase, reaching 0.6 at lower temperatures.

Journal Article↗
PubMed2005

Highly efficient endogenous human gene correction using designed zinc-finger nucleases.

Permanent modification of the human genome in vivo is impractical owing to the low frequency of homologous recombination in human cells, a fact that hampers biomedical research and progress towards safe and effective gene therapy. Here we report a general solution using two fundamental biological processes: DNA recognition by C2H2 zinc-finger proteins and homology-directed repair of DNA double-strand breaks. Zinc-finger proteins engineered to recognize a unique chromosomal site can be fused to a nuclease domain, and a double-strand break induced by the resulting zinc-finger nuclease can create specific sequence alterations by stimulating homologous recombination between the chromosome and an extrachromosomal DNA donor. We show that zinc-finger nucleases designed against an X-linked severe combined immune deficiency (SCID) mutation in the IL2Rgamma gene yielded more than 18% gene-modified human cells without selection. Remarkably, about 7% of the cells acquired the desired genetic modification on both X chromosomes, with cell genotype accurately reflected at the messenger RNA and protein levels. We observe comparably high frequencies in human T cells, raising the possibility of strategies based on zinc-finger nucleases for the treatment of disease.

Alleles↗
PubMed2002

TRF2 associates with DREF and directs promoter-selective gene expression in Drosophila.

Drosophila TATA-box-binding protein (TBP)-related factor 2 (TRF2) is a member of a family of TBP-related factors present in metazoan organisms. Recent evidence suggests that TRF2s are required for proper embryonic development and differentiation. However, true target promoters and the mechanisms by which TRF2 operates to control transcription remain elusive. Here we report the antibody affinity purification of a Drosophila TRF2-containing complex that contains components of the nucleosome remodelling factor (NURF) chromatin remodelling complex as well as the DNA replication-related element (DRE)-binding factor DREF. This latter finding led us to potential target genes containing TRF2-responsive promoters. We have used a combination of in vitro and in vivo assays to show that the DREF-containing TRF2 complex directs core promoter recognition of the proliferating cell nuclear antigen (PCNA) gene. We also identified additional TRF2-responsive target genes involved in DNA replication and cell proliferation. These data suggest that TRF2 functions as a core promoter-selectivity factor responsible for coordinating transcription of a subset of genes in Drosophila.

Animals↗
PubMed2002

Compartmentalization of macrophage inflammatory protein-2, but not cytokine-induced neutrophil chemoattractant, in rats challenged with intratracheal endotoxin.

An important feature of the pulmonary inflammatory response is that the production of certain cytokines and chemokines is largely confined to the lung. This study investigated the local and systemic responses of macrophage inflammatory protein-2 (MIP-2) and cytokine-induced neutrophil chemoattractant (CINC) in rats administered with either intratracheal or intravenous lipopolysaccharide (LPS). Intratracheal LPS induced a significant increase in MIP-2 in bronchoalveolar lavage (BAL) fluid with no detectable MIP-2 in the plasma. In contrast, CINC was significantly increased in both BAL fluid and the plasma after intratracheal LPS challenge. Cell-associated MIP-2 was increased in the pulmonary-recruited neutrophils (PMNs) but not in the circulating PMNs in rats given intratracheal LPS. Cell-associated CINC was increased in both the recruited and circulating PMNs in these animals. Intravenous LPS caused a marked increase in plasma MIP-2 and CINC, whereas only a small elevation of both MIP-2 and CINC concentrations in BAL fluid was observed. The lack of CINC compartmentalization compared to MIP-2 implies that these C-X-C chemokines are regulated differentially and may have different effects upon polymorphonuclear leukocyte (PMN) recruitment into the alveolar space in response to intrapulmonary LPS or bacterial challenge.

Animals↗
PubMed2002

Neutrophil modulation of the pulmonary chemokine response to lipopolysaccharide.

When cells within the intrapulmonary compartment are exposed to pathogens or their products such as lipopolysaccharide, they produce CXC chemokines in order to attract circulating neutrophils into the lower respiratory tract. Previous studies have shown that as neutrophils (PMNs) enter the lung, bronchoalveolar lavage (BAL) chemokine levels are decreased. In this study, we determined the intrapulmonary and systemic responses to two important rat chemokines, cytokine-induced neutrophil chemoattractant (CINC) and macrophage inflammatory protein-2 (MIP-2), to intratracheal (i.t.) LPS (100 microg in 0.5 mL of phosphate-buffered saline) under neutropenic (cyclophosphamide [CPA]) and neutrophilic (G-CSF) conditions. By 4 h after i.t. LPS, CPA pretreatment decreased PMN recruitment 83% and G-CSF increased PMN recruitment 91% compared with recruitment into the lung in vehicle-pretreated rats (42.7 +/- 19.3 million PMNs). Neutropenic rats had increased CINC and MIP-2 concentrations in BAL fluid 4 h after i.t. LPS when compared with levels seen in vehicle controls (P < 0.05). In vitro LPS-stimulated chemokine production by alveolar macrophages obtained from CPA- and vehicle-pretreated animals did not differ. The increase in BAL fluid chemokine levels in neutropenic rats corresponded to increased chemotaxis of neutrophils to BAL fluid from CPA-pretreated rats as compared with the chemotaxis response of PMN to BAL fluid from vehicle-pretreated rats. In contrast, G-CSF enhancement of neutrophil recruitment decreased chemotactic activity of BAL fluid collected 4 h after i.t. LPS. These data show that as neutrophils are recruited into the lung, they alter chemokine levels, which most likely serves to down-regulate the inflammatory response.

Animals↗