Biomedical subjects

Steven G Thomas

Publications and source records attributed to Steven G Thomas.

5 recordsLinked to original sources

PubMed2006

Actin depolymerization is sufficient to induce programmed cell death in self-incompatible pollen.

Self-incompatibility (SI) prevents inbreeding through specific recognition and rejection of incompatible pollen. In incompatible Papaver rhoeas pollen, SI triggers a Ca2+ signaling cascade, resulting in the inhibition of tip growth, actin depolymerization, and programmed cell death (PCD). We investigated whether actin dynamics were implicated in regulating PCD. Using the actin-stabilizing and depolymerizing drugs jasplakinolide (Jasp) and latrunculin B, we demonstrate that changes in actin filament levels or dynamics play a functional role in initiating PCD in P. rhoeas pollen, triggering a caspase-3-like activity. Significantly, SI-induced PCD in incompatible pollen was alleviated by pretreatment with Jasp. This represents the first account of a specific causal link between actin polymerization status and initiation of PCD in a plant cell and significantly advances our understanding of the mechanisms involved in SI.

Actin Cytoskeleton↗

PubMed2005

Fluorescence fibre-optic confocal microscopy of skin in vivo: microscope and fluorophores.

BACKGROUND/AIMS: Fibre-optic confocal imaging in vivo is a new approach in the assessment of human skin. The objective is to describe a novel instrument and its operation and use in combination with fluorophores. METHODS: The Stratum is a fibre-optic fluorescence confocal microscope especially developed for the study of skin and mucous membranes. The system is flexible and any body site can be studied with a hand-held scanner. The light source is a 488 nm argon ion laser. Horizontal (en face) images of the epidermis and outer dermis are produced with cellular resolution. Magnification is approximately 1000 x . Fluorescein sodium is routinely used as fluorophore (intradermal injection or application to the skin surface). This fluorophore is safe for human use in vivo, but other substances (rhodamine B, Acridine Orange, green fluorescent protein, curcumin) have also been studied. RESULTS: The instrument produces sharp images of epidermal cell layers from the epidermal surface to the sub-papillary dermis, with sub-cellular resolution. The scanner is flexible in use. The technique of intradermal fluorophore injection requires some skill. CONCLUSIONS: We consider this fibre-optic instrument a potentially important tool in skin research for non-invasive optical biopsy of primarily the epidermis. Present use is focussed on research applications, where the fluorophore distribution in the skin may illustrate morphological changes in the epidermis.

Dermoscopy↗

PubMed2004

Self-incompatibility triggers programmed cell death in Papaver pollen.

Sexual reproduction in many angiosperm plants involves self-incompatibility (SI), which is one of the most important mechanisms to prevent inbreeding. SI is genetically controlled by the S-locus, and involves highly specific interactions during pollination between pollen and the pistil on which it lands. This results in the rejection of incompatible ('self') pollen, whereas compatible ('non-self') pollen is allowed to fertilize the plant. In Papaver rhoeas, S-proteins encoded by the stigma component of the S-locus interact with incompatible pollen, triggering a Ca2+-dependent signalling network, resulting in the inhibition of pollen-tube growth. Programmed cell death (PCD) is a mechanism used by many organisms to destroy unwanted cells in a precisely regulated manner. Here we show that PCD is triggered by SI in an S-specific manner in incompatible pollen. This provides a demonstration of a SI system using PCD, revealing a novel mechanism to prevent self-fertilization. Furthermore, our data reveal that the response is biphasic; rapid inhibition of pollen-tube growth is followed by PCD, which is involved in a later 'decision-making' phase, making inhibition irreversible.

Animals↗

PubMed2003

View of normal human skin in vivo as observed using fluorescent fiber-optic confocal microscopic imaging.

Fluorescence confocal scanning laser microscopy, using a miniaturized handheld scanner, was performed to visualize the microscopic architecture of normal human epidermis in vivo. Fluorescein sodium (approximately 20 microL of 0.2% wt/vol) was administered via intradermal injection to normal skin on the volar forearm of 22 patients. The skin was imaged continuously from 1 to 15 min after injection. Fluorescein was excited at 488 nm and the fluorescent emission was detected at > 505 nm. In each subject, a series of images was collected at increasing depth, from superficial stratum corneum to papillary dermis. Features observed in confocal images were compared to those seen in hematoxylin- and eosin-stained sections of skin. The confocal images demonstrated the architecture of superficial skin in the horizontal plane. There was a transition in keratinocyte size, shape, and morphology with progressive imaging into the deeper epidermal layers. Superficial dermis and microscopic capillaries with blood flow were easily observed. The morphologic patterns associated with the major cell types of the epidermis were consistent with those known from conventional histology. We report the ability of in vivo fluorescence point scanning laser confocal microscopy to produce real-time, high-resolution images of the microscopic architecture of normal human epidermis using a noninvasive imaging technology.

Adult↗

PubMed2002

In vivo detection of morphological and microvascular changes of the colon in association with colitis using fiberoptic confocal imaging (FOCI).

Using a well-established rodent model of inflammatory bowel disease (IBD), the present study examined changes in the microvasculature of the colonic mucosa in association with ulcerative colitis (UC). The results were compared to microscopic alterations in tissue morphology to establish a temporal relationship between microcirculatory dysfunction and IBD pathology. Mild colitis was induced in rats by the oral consumption of 5% dextran sulfate sodium (DSS) in drinking water. Control animals were provided with water ad libitum. After 3, 5, and 7 days of oral ingestion of DSS, anesthetized rats were laparotomized. The mucosal surface of the distal colon was then examined using fiber optic confocal imaging (FOCI; excitation 488 nm argon ion laser, detection above 515 nm). Changes in the mucosal architecture were examined following the topical application of the fluorescent dye, tetracycline hydrochloride. Tetracycline hydrochloride, an antibiotic used widely in clinical medicine, enabled imaging of the crypts at the surface of the mucosa. Spatial changes in the microvascular structure were assessed following the intravenous administration of fluorescein isothiocyanate dextran (FITC-dextran). Confocal images were correlated with clinical parameters, including weight loss, occult blood, and stool consistency. Attenuation of the colonic epithelium was detected on day 3 colitis. Morphological changes including crypt loss, crypt distortion, and inflammatory cell infiltrate were detected on day 5 and day 7 colitis. Dual channel imaging showed the mucosal capillary network outlining the stromal confines of the mucus-secreting glands in control tissue. Experimental colitis resulted in diffuse hypervascularity and tortuosity of the capillary vessels. Evidence of increased vessel leakiness (leakage of FITC-dextran from the lumen) was first detected on day 5 colitis. Complete disruption of the normal honeycomb pattern of the vessels and capillary dilation was evident after 7 days of DSS ingestion. These findings suggest that the pathogenesis of ulcerative colitis is associated with changes in the vascular architecture as demonstrated in vivo using confocal microscopy.

Animals↗