Biomedical subjects

Laelie A Snook

Publications and source records attributed to Laelie A Snook.

5 recordsLinked to original sources

PubMed2006

Fungal surface remodelling visualized by atomic force microscopy.

Most fungal growth is localized to the tips of hyphae, however, early stages of spore germination and the growth of certain morphological mutant strains exhibit non-polarized expansion. We used atomic force microscopy (AFM) to document changes in Aspergillus nidulans wall surfaces during non-polarized growth: spore germination, and growth in a strain containing the hypA1 temperature sensitive morphogenesis defect. We compared wall surface structures of both wild-type and mutant A. nidulans following growth at 28 degrees and 42 degrees C, the latter being the restrictive temperature for hypA1. There was no appreciable difference in surface ultrastructure between wild-type and hypA1 spores, or hyphal walls grown at 28 degrees C. When dry mature A. nidulans conidia were wetted they lost their hydrophobin coat, indicating an intermediate stage between dormancy and swelling. The surface structure of hypA1 germlings grown at 42 degrees C was less organized than wild-type hyphae grown under the same conditions, and had a larger range of subunit sizes. AFM images of hyphal wall surface changes following a shift in growth temperature from restrictive (42 degrees C) to permissive (28 degrees C), showed a gradient of sizes for wall surface features similar to the trend observed for wild-type cells at branch points. Changes associated with the hyphal wall structure for A. nidulans hypA1 offer insight into the events associated with fungal germination, and wall remodelling.

Aspergillus nidulans↗

PubMed2006

Mu-delta opioid receptor functional interaction: Insight using receptor-G protein fusions.

Fusion proteins between a receptor and a pertussis toxin-insensitive G(i)alpha subunit were used to gain insight into the molecular interactions that take place upon mu and delta opioid receptor heterodimerization. When mu opioid receptor-G(i1)alpha fusions were coexpressed with nonfused delta opioid receptors in human embryonic kidney 293 cells, or vice versa, receptor heterodimers were detected by coimmunoprecipitation. In pertussis toxin-treated cells, receptor coexpression decreased the amount of guanosine 5'-O-(3-[35S]thio)triphosphate ([35S]GTPgammaS) incorporated in the fused G alpha protein after the addition of agonists specific for the receptor-G(i1)alpha fusion. In addition, activation of the G alpha protein occurred in heterodimers upon addition of an agonist specific for the nonfused receptor. It remained unaffected by an inverse agonist specific for the receptor-G(i1)alpha fusion. These data suggest that signaling through the receptor-G(i1)alpha fusion protein is impaired in heterodimers and support a mechanism in which activation of the G alpha subunit is promoted by a direct interaction with the nonfused receptor. Alternatively, receptor coexpression did not modify the ligand binding properties for the high-affinity state of the receptor-G(i1)alpha fusion nor the EC50 values for agonist-induced [35S]GTPgammaS incorporation in the G(i1)alpha subunit. In addition, no binding competition was observed between delta and mu ligands. Together, the data point to mu-delta opioid receptor heterodimers formed by contact interactions between monomers that retain their structural integrity.

Analgesics, Opioid↗

PubMed2005

Surface ultrastructure and elasticity in growing tips and mature regions of Aspergillus hyphae describe wall maturation.

This study reports the first direct, high-resolution physical and structural evidence of wall changes during hyphal tip growth, visualized by atomic force microscopy (AFM) in Aspergillus nidulans. Images from AFM and cryo-scanning electron microscopy provided comparable information, but AFM was also able to image and physically probe living cells. AFM images showed changes in the surface ultrastructure of A. nidulans hyphae, from newly deposited walls at hyphal tips to fully mature walls, as well as additional changes at young branches arising from mature walls. Surface architecture during wall maturation correlated with changes in the relative viscoelasticity (compliance per unit applied force) of walls measured by force spectroscopy (FS) in growing A. nidulans hyphae. Growing tips showed greater viscoelasticity than mature walls, despite equal support from turgor. Branch tips had comparable viscoelasticity to hyphal tips, unlike the mature wall from which they grew. FS also revealed differences in surface hydrophilicity between newly deposited and mature walls, with the tips being more hydrophilic. The hydrophilicity of young branch tips was similar to that of hyphal tips, and different from that of mature walls. Taken together, AFM images and FS data suggest that the A. nidulans wall matures following deposition at the hyphal tip.

Aspergillus nidulans↗

PubMed2005

Development of a triplex real-time PCR assay for detection of Panton-Valentine leukocidin toxin genes in clinical isolates of methicillin-resistant Staphylococcus aureus.

Community-associated methicillin-resistant Staphylococcus aureus harboring Panton-Valentine leukocidin (PVL) genes is an emerging pathogen. A novel real-time PCR assay for identification of MRSA isolates containing PVL was developed. The PVL assay was used in a triplex format allowing simultaneous amplification of mecA, nuc, and PVL genes in 614 clinical isolates. This assay facilitates the rapid identification of PVL-positive isolates of MRSA.

Bacterial Toxins↗

PubMed2002

Expression of the human mu opioid receptor in a stable Sf9 cell line.

The cDNA that encodes the human mu opioid receptor (hMOR) has been cloned and expressed in Spodoptera frugiperda (Sf9) cells using a nonlytic vector system. The coding sequence fused to the cleavable glycoprotein signal peptide gp 64, and a C-terminal histidine tag was placed under the transcriptional control of the Orgyia pseudotsugata multicapsid nucleopolyhedrosis virus immediate-early 2 (OpIE2) promoter. Transfected cells were selected using Zeocin resistance and the receptor was constitutively expressed at approximately 12000 receptors per cell. Immunofluorescence images illustrated that more than 75% of the Sf9 cells expressed hMOR at the plasma membrane. This is the first report of the constitutive and heterologous expression of a G protein-coupled receptor in a stably transfected Sf9 cell line, under the control of the OpIE2 promoter.

Animals↗