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T H Smith

Publications and source records attributed to T H Smith.

At least 19 recordsLinked to original sources
PubMed2000

Plant viral suppressors of post-transcriptional silencing do not suppress transcriptional silencing.

Homology-dependent gene silencing is a regulatory mechanism that limits RNA accumulation from affected loci either by suppression of transcription (transcriptional gene silencing, TGS) or by activation of a sequence-specific RNA degradation process (post-transcriptional gene silencing, PTGS). The P1/HC-Pro sequence of plant potyviruses and the 2b gene of the cucumber mosaic virus have been shown to interfere with PTGS. The ability of these viral suppressors of PTGS to interfere with TGS was tested using the 271 locus which imposes TGS on transgenes under 35S or 19S promoters and PTGS on the endogenous nitrite reductase gene (Nii). Both P1/HC-Pro and 2b reversed PTGS of Nii genes in 271-containing tobacco plants, but failed to reverse TGS of 35S-GUS transgenes in the same plant. P1/HC-Pro expression from a transgene also failed to suppress either the initiation or maintenance of TGS imposed by the NOSpro-silencing locus, H2. These results indicate that PTGS and TGS operate through unlinked pathways or that P1/HC-Pro and 2b interfere at step(s) in PTGS that are downstream of any common components in the two pathways. The data suggest a simple assay to identify post-transcriptionally silenced transgenic lines with the potential to be stably converted to high expressing lines.

Cucumovirus↗
PubMed1999

A left atrial myxoma presenting as a cerebrovascular accident.

A 14-year-old female presented with common clinical findings for a rare primary intracardiac tumor. Primary cardiac tumors are rare in all age groups, occurring in 0.05% of routine postmortem examinations. Pediatric primary cardiac tumors are likewise uncommon, with the most common being a rhabdomyoma. Atrial myxomas occur infrequently in the pediatric age group. They occur primarily between the third and sixth decade, making them the most common adult primary cardiac tumor. The following case presentation demonstrates a common clinical presentation for an intracardiac mass rarely diagnosed in the pediatric population. This patient's acute neurologic symptoms required prompt recognition of an intracardiac etiology. This recognition proved critical for the acute and long-term medical and surgical management of this patient.

Adolescent↗
PubMed1998

A viral suppressor of gene silencing in plants.

Gene silencing is an important but little understood regulatory mechanism in plants. Here we report that a viral sequence, initially identified as a mediator of synergistic viral disease, acts to suppress the establishment of both transgene-induced and virus-induced posttranscriptional gene silencing. The viral suppressor of silencing comprises the 5'-proximal region of the tobacco etch potyviral genomic RNA encoding P1, helper component-proteinase (HC-Pro) and a small part of P3, and is termed the P1/HC-Pro sequence. A reversal of silencing assay was used to assess the effect of the P1/HC-Pro sequence on transgenic tobacco plants (line T4) that are posttranscriptionally silenced for the uidA reporter gene. Silencing was lifted in offspring of T4 crosses with four independent transgenic lines expressing P1/HC-Pro, but not in offspring of control crosses. Viral vectors were used to assess the effect of P1/HC-Pro expression on virus-induced gene silencing (VIGS). The ability of a potato virus X vector expressing green fluorescent protein to induce silencing of a green fluorescent protein transgene was eliminated or greatly reduced when P1/HC-Pro was expressed from the same vector or from coinfecting potato virus X vectors. Expression of the HC-Pro coding sequence alone was sufficient to suppress virus-induced gene silencing, and the HC-Pro protein product was required for the suppression. This discovery points to the role of gene silencing as a natural antiviral defense system in plants and offers different approaches to elucidate the molecular basis of gene silencing.

Journal Article↗
PubMed1998

Outbreak of mastitis caused by one strain of Staphylococcus aureus in a closed dairy herd.

The Washington State University dairy experienced an outbreak of intramammary infections (IMI) caused by Staphylococcus aureus during autumn 1993 through summer 1995. The outbreak was believed to be a result of transmission of 1 strain of S aureus in a herd that historically had excellent control of contagious mastitis. Control practices included strict hygiene at time of milking and preferential culling of cows infected with S aureus. Mastitis caused by Streptococcus agalactiae was not found in this herd. Despite excellent control practices, the strain of S aureus caused a new infection rate of approximately 3% of the herd per month. Moreover, a second strain of S aureus, isolated from a cow with mastitis, was introduced into the herd experimentally, and it failed to transmit disease. The outbreak of S aureus mastitis in this herd was eventually controlled by maintaining a program of strict milking time hygiene, by intensifying the program of preferentially culling infected cows, and by segregating cows with S aureus IMI in a separate pen and milking these infected cows last.

Animals↗
PubMed1998

Cleavage susceptibility of reovirus attachment protein sigma1 during proteolytic disassembly of virions is determined by a sequence polymorphism in the sigma1 neck.

A requisite step in reovirus infection of the murine intestine is proteolysis of outer-capsid proteins to yield infectious subvirion particles (ISVPs). When converted to ISVPs by intestinal proteases, virions of reovirus strain type 3 Dearing (T3D) lose 90% of their original infectivity due to cleavage of viral attachment protein sigma1. In an analysis of eight field isolate strains of type 3 reovirus, we identified one additional strain, type 3 clone 31 (T3C31), that loses infectivity and undergoes sigma1 cleavage upon conversion of virions to ISVPs. We examined the sigma1 deduced amino acid sequences of T3D and the eight field isolate strains for a correlation between sequence variability and sigma1 cleavage. The sigma1 proteins of T3D and T3C31 contain a threonine at amino acid position 249, whereas an isoleucine occurs at this position in the sigma1 proteins of the remaining strains. Thr249 occupies the d position of a heptad repeat motif predicted to stabilize sigma1 oligomers through alpha-helical coiled-coil interactions. This region of sequence comprises a portion of the fibrous tail domain of sigma1 known as the neck. Substitution of Thr249 with isoleucine or leucine resulted in resistance to cleavage by trypsin, whereas replacement with asparagine did not affect cleavage susceptibility. These results demonstrate that amino acid position 249 is an independent determinant of T3D sigma1 cleavage susceptibility and that an intact heptad repeat is required to confer cleavage resistance. We performed amino-terminal sequence analysis on the sigma1 cleavage product released during trypsin treatment of T3D virions to generate ISVPs and found that trypsin cleaves sigma1 after Arg245. Thus, the sequence polymorphism at position 249 controls cleavage at a nearby site in the neck region. The relevance of these results to reovirus infection in vivo was assessed by treating virions with the contents of a murine intestinal wash under conditions that result in generation of ISVPs. The pattern of sigma1 cleavage susceptibility generated by using purified protease was reproduced in assays using the intestinal wash. These results provide a mechanistic explanation for sigma1 cleavage during exposure of virions to intestinal proteases and may account for certain strain-dependent patterns of reovirus pathogenesis.

Base Sequence↗
PubMed1997

A cationic lipid for rapid and efficient delivery of plasmid DNA into mammalian cells.

Cationic lipids are widely used for gene transfer into cultured eukaryotic cells. However, lipids with potent transfection activity are often associated with high levels of cytotoxicity, and also require serum-free conditions for optimal performance. These characteristics in many cases result in unsatisfactory transfection efficiency. In this report, we describe a new cationic amphiphile, N-t-butyl-N'-tetradecyl-3-tetradecylaminopropionamidine (Amidine). Amidine requires only 1-2 hour incubation intervals to produce maximal transfection efficiency, and can transfect cells in the presence of serum. Such characteristics significantly minimize cytotoxicity, and also provide time flexibility for researchers. We routinely obtain over 80% transfection efficiency as evidenced by use of an enhanced green fluorescence protein (EGFP) as the reporter. These studies demonstrate the utility of Amidine for rapid and efficient transfection of mammalian cells.

Animals↗
PubMed1997

Rainbow Universal CPG: a versatile solid support for oligonucleotide synthesis.

We have developed a universal solid support, termed Rainbow Universal CPG, for use in automated oligonucleotide synthesis. The universal solid support allows any oligodeoxyribonucleotide sequence to be synthesized from a single type of controlled pore glass (CPG) support. Deprotection of oligodeoxyribonucleotides was optimized using 0.5 M LiCl in concentrated ammonium hydroxide. PCR experiments using three different sets of primers proved that the 3'-hydroxyl function of oligodeoxyribonucleotides synthesized from Rainbow Universal CPG was retained. This universal solid support shows promise for replacing the standard nucleoside CPG supports.

Automation↗
PubMed1994

Somite subdomains, muscle cell origins, and the four muscle regulatory factor proteins.

We show by immunohistology that distinct expression patterns of the four muscle regulatory factor (MRF) proteins identify subdomains of mouse somites. Myf-5 and MyoD are, at specific stages, each expressed in both myotome and dermatome cells. Myf-5 expression is initially restricted to dorsal cells in all somites, as is MyoD expression in neck somites. In trunk somites, however, MyoD is initially expressed in ventral cells. Myogenin and MRF4 are restricted to myotome cells, though the MRF4-expressing cells are initially less widely distributed than the myogenin-expressing cells, which are at all stages found throughout the myotome. All somitic myocytes express one or more MRFs. The transiently distinct expression patterns of the four MRF proteins identify dorsal and ventral subdomains of somites, and suggest that skeletal muscle cells in somites originate at multiple sites and via multiple molecular pathways.

Animals↗
PubMed1993

Pulmonary metastases in children and young adults with differentiated thyroid cancer.

BACKGROUND: The prognostic significance and optimal care of children with differentiated thyroid cancer and pulmonary metastases are not well established. METHODS: Of 209 patients younger than 25 years of age who were treated at University of Texas M. D. Anderson Cancer Center between 1960 and 1990 and for whom there was sufficient information, 19 (9%) had pulmonary metastases at presentation. RESULTS: All of these patients had regional lymphadenopathy at the time of diagnosis. All but two had intense, diffuse radioiodine uptake in the lungs; there were two false-negative scans immediately after surgical procedure caused by competing thyroid residual. The chest radiograph (CXR) was normal in 8 of 17 (42%) patients with abnormal radioiodine scans. After therapy with radioiodine (100-499 mCi), CXR appeared normal in 7 of 9 patients with initial abnormal radiographs (within 6-75 months). Radioiodine uptake by the lungs normalized in 3 of 8 patients with initially normal radiographs, and in 3 of 9 patients with initially abnormal radiographs. There have been no deaths in these 19 patients. CONCLUSION: Pulmonary metastases are not uncommon in children and young adults with differentiated thyroid cancer, especially those who have regional lymphadenopathy. The lung metastases almost always concentrate radioiodine diffusely and may be associated with a normal CXR in almost half of the patients. Pulmonary metastases may be overlooked unless near total thyroidectomy is followed by total body radioiodine scan (TBS) in all children and young adults who have regional lymphadenopathy of the neck.

Adenocarcinoma↗
PubMed1993

Hidden sugars.

Explore the source record for details and available documents.

Acids↗
PubMed1993

Cellular and molecular diversity in skeletal muscle development: news from in vitro and in vivo.

Skeletal muscle formation is studied in vitro with myogenic cell lines and primary muscle cell cultures, and in vivo with embryos of several species. We review several of the notable advances obtained from studies of cultured cells, including the recognition of myoblast diversity, isolation of the MyoD family of muscle regulatory factors, and identification of promoter elements required for muscle-specific gene expression. These studies have led to the ideas that myoblast diversity underlies the formation of the multiple types of fast and slow muscle fibers, and that myogenesis is controlled by a combination of ubiquitous and muscle-specific transcriptional regulators that may be different for each gene. We further review some unexpected results that have been obtained when ideas from work in culture have been tested in developing animals. The studies in vivo point to additional molecular and cellular mechanisms that regulate muscle formation in the animal.

Animals↗
PubMed1993

A unique pattern of expression of the four muscle regulatory factor proteins distinguishes somitic from embryonic, fetal and newborn mouse myogenic cells.

A unique pattern of expression of the four muscle regulatory factor (MRF) proteins was found to distinguish early somitic from embryonic, fetal and newborn limb myogenic cells in vitro. Expression of the myosin heavy chain (MHC), MyoD, myogenin, Myf-5, and MRF4 proteins was examined by immunocytochemistry in cultures of four distinct types of mouse myogenic cells: somitic (E8.5), embryonic (E11.5), fetal (E16.5) and newborn limb. In embryonic, fetal and newborn cultures, the MRF proteins were expressed in generally similar patterns: MyoD was the first MRF expressed; MyoD and myogenin were expressed by more cells than Myf-5 or MRF4; and each of the four MRFs was found both in cells that expressed MHC and in cells that did not express MHC. In cultures of somitic cells, in contrast, Myf-5 was expressed first and by more cells than MyoD or myogenin; MRF4 was not detected; and the MRFs were never found to be coexpressed with MHC in the same cell. Thus, some somitic cells had the unexpected ability to maintain MHC expression in the absence of detectable MRF protein expression. The different myogenic programs of embryonic, fetal and newborn myogenic cells are not, therefore, a simple result of qualitatively different MRF expression patterns, whereas myogenesis by somitic cells does include a unique pattern of MRF expression.

Animals↗
PubMed1992

Looking back and looking forward.

'Forty years back and forty years on' was the title of the address given by Francis Manfield at the annual meeting of the RCS of England in December 1970. Francis, twice president of the Middx & Herts Branch, which this year celebrates its first 40 years, started in practice in 1930, so he was well qualified to look back over those 40 years. The aspects of change in dentistry, 1930-1970, make arresting reading more than 20 years later. His predictions for the future are equally interesting.

Dental Instruments↗
PubMed1992

Distinct myogenic programs of embryonic and fetal mouse muscle cells: expression of the perinatal myosin heavy chain isoform in vitro.

Early embryonic and late fetal mouse myogenic cells showed distinct patterns of perinatal myosin heavy chain (MHC) isoform expression upon differentiation in vitro. In cultures of somite or limb muscle cells isolated from Day 9 to Day 12 embryos, differentiated cells that expressed perinatal MHC were rare and perinatal MHC was not detectable by immunoblotting. In cultures of limb muscle cells isolated from Day 13 to Day 18 fetuses, in contrast, the perinatal MHC isoform was easily detected and was expressed in a substantial percentage of myocytes and myotubes. Analyses of clonally derived muscle colonies and cytosine arabinoside-treated fetal muscle cell cultures suggested that different fetal muscle cell nuclei initiated perinatal MHC expression at different times. In both embryonic and fetal cell cultures, the embryonic MHC isoform was expressed by all differentiated cells examined. A small number of myotubes in fetal muscle cell cultures showed a mosaic distribution of MHC isoform accumulation in which the perinatal MHC isoform accumulated in a restricted region of the myotube near particular nuclei, whereas the embryonic MHC isoform accumulated throughout the myotube. Thus, the myogenic program of fetal, but not embryonic, mouse myogenic cells includes expression of the perinatal MHC isoform upon differentiation in culture.

Animals↗
PubMed1991

Wolf syndrome.

Since the initial description in 1965 of Wolf syndrome, or deletion of the short arm of chromosome number four, over one hundred cases have been reported. Much less, however, has been published on the radiologic findings in this disorder. We report a case with both typical and unusual features of the 4p- syndrome, including "bottle opener" deformity of the clavicles, and review the relevant literature.

Abnormalities, Multiple↗
PubMed1991

Seatbelt induced chance fracture in an infant. Case report and literature review.

Chance ("seat belt") fractures of the lumbar spine are extremely rare in the pediatric population and virtually unheard of in infants. We report a case of a 14 month old boy sustaining an isolated Chance fracture to L1 without associated spinal subluxation, dislocation, neurologic or visceral injury. He was being breast fed with his back beneath the passenger side shoulder harness when the vehicular front end collision causing his injury occurred. Thus, he may actually have sustained a hyperextension distraction or "Reverse Chance" fracture.

Accidents, Traffic↗