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Biomedical subjects

A F Holloway

Publications and source records attributed to A F Holloway.

At least 19 recordsLinked to original sources
PubMed2000

Functional interaction between the HIV transactivator Tat and the transcriptional coactivator PC4 in T cells.

The human immunodeficiency virus (HIV) transactivator Tat is a potent activator of transcription from the HIV long terminal repeat and is essential for efficient viral gene expression and replication. Tat has been shown to interact with components of the basal transcription machinery and transcriptional activators. Here we identify the cellular coactivator PC4 as a Tat-interacting protein using the yeast two-hybrid system and confirmed this interaction both in vitro and in vivo by coimmunoprecipitation. We found that this interaction has a functional outcome in that PC4 overexpression enhanced activation of the HIV long terminal repeat in transient transfection studies in a Tat-dependent manner. The domains of PC4 and Tat required for the interaction were mapped. In vitro binding studies showed that the basic transactivation-responsive binding domain of Tat is required for the interaction with PC4. The minimum region of PC4 required for Tat binding was amino acids 22-91, whereas mutation of the lysine-rich domain between amino acids 22 and 43 prevented interaction with Tat. Tat-PC4 interactions may be controlled by phosphorylation, because phosphorylation of PC4 by casein kinase II inhibited interactions with Tat both in vivo and in vitro. We propose that PC4 may be involved in linking Tat to the basal transcription machinery.

Amino Acid Sequence↗
PubMed1997

Metallothioneins 1 and 2 are expressed in the olfactory mucosa of mice in untreated animals and during the regeneration of the epithelial layer.

We have examined the expression of the MT1 and MT2 isoforms of metallothionein in the mouse olfactory mucosa. In untreated mice, metallothionein was strongly expressed in supporting cells, acinar cells of the Bowman's glands, and olfactory neurons. Expression was however restricted to a subset of cells within each type, and to zones within the olfactory system. Irrigation with ZnSO4 solution caused exfoliation of the olfactory epithelium and during the resultant regeneration, metallothionein immunoreactivity was associated with the proliferating basal cells. The ability to express MTs 1 and 2 did not appear to be obligatory for the early stages of regeneration since mice which do not express these isoforms responded similarly to wild type mice. Strong nuclear expression of metallothionein was noted in the untreated olfactory chamber following unilateral irrigation.

Animals↗
PubMed1997

Human metallothionein gene MT1L mRNA is present in several human tissues but is unlikely to produce a metallothionein protein.

A human MT gene from the functional locus on chromosome 16, MT1L, is characterised and shown to produce mRNA in at least four human tissues. This gene is unlikely to produce a metallothionein protein because it contains a termination codon at position 26, by analogy to other human MT1 genes. MT1L cDNA is almost identical to another metallothionein cDNA clone reported recently, MT1R, suggesting that either there are unmapped human metallothionein genes, or that MT1L is polymorphic.

Amino Acid Sequence↗
PubMed1997

Localisation and expression of metallothionein immunoreactivity in the developing sheep brain.

Metallothioneins are small cysteine-rich proteins that bind heavy metals. In higher mammals there are complex families of metallothionein isoforms, which are well characterised at the DNA level but less so in terms of their cellular expression and function. In particular, little is known about the localisation of metallothionein in the developing mammalian brain. In this study using sheep fetuses, we have shown that metallothionein 1 and 2 isoform expression undergoes shifts in regional and cellular localisation during development of the brain. Metallothionein 1 and 2 expression is first detected by embryonic days E72 E73 (gestation is 150 days) at the mRNA level and the metallothionein protein is observed in cells of the proliferating ventricular zones. Subsequent expression is detected in radial glial cells, oligodendrocytes and astrocytes in several regions of the brain, most notably the cerebral cortex. In the adult brain, metallothionein is expressed in astrocytes but not in oligodendrocytes. Double-labelling immunohistochemistry using the glial fibrillary acidic protein (GFAP) an astrocyte marker, and metallothionein revealed that although there is an overlap in the profiles of the two proteins, there is no simple correlation in their expression. These observations are consistent with metallothionein, under physiological conditions, being regulated mainly by intracellular factors.

Aging↗
PubMed1995

The spectrum and angular distribution of x rays scattered from a water phantom.

To calculate the response of an image receptor to the x rays emerging from a scattering medium, it is necessary to know the x-ray spectrum and intensity as a function of the angle of incidence on the receptor. To permit this calculation for any x-ray spectrum incident on a medium, these functions must be known for monoenergetic x rays. For monoenergetic x rays in the range 20-70 keV we have measured with a high-purity germanium detector the spectrum and intensity of x rays emitted from a water phantom at angles of 0 degree-50 degrees to the direction of the primary beam. The spectrum and intensity of emitted x rays have also been calculated by the Monte Carlo method. At small exit angles, most of the x rays have energies close to the incident energy. As the exit angle increases, the fraction of multiply scattered x rays increases. At very large exit angles, the dominant feature of the spectrum is the peak due to these multiply scattered x rays. For small scattering angles the Monte Carlo calculations are in good agreement with the measurements over the range of energies. For large scattering angeles the scattered photon fluence predicted by Monte Carlo modeling is consistently lower than the measurement in the region just below the full energy peak. The cause of the discrepancies is not fully understood, but cannot be accounted for by Compton broadening alone. An alternate approach to model incoherent scattering is proposed.

Humans↗
PubMed1994

Characterisation of six additional human metallothionein genes.

Human metallothionein (MT) genes are clustered in a locus on chromosome 16, and this report presents the characterisation of the remaining six univestigated members of the family. Nucleotide sequencing in whole or part suggested that four of these genes, MT1I, MT1J, MT1K and MT1L do not encode expressed MT proteins, based on the presence of structural faults or atypical amino acid assignments. On the other hand, the structures of MT1H and MT1X are consistent with these genes being functional and encoding unique type 1 isoforms. The promoters of both genes conferred activity to CAT expression constructs when transfected into HeLa cells, and showed differential responses to inducers MT synthesis. Endogenous MT1H and MT1X genes were expressed at the mRNA level in HeLa cells following cadmium treatment. This work brings the number of functional class 1 and 2 MT genes in the human to eight, and confirms that each encodes structurally unique proteins.

Amino Acid Sequence↗
PubMed1984

Dose and quality control (DQC) in diagnostic radiology.

Dose and quality control in diagnostic radiology can play an important role in reducing x-ray exposure and costs whilst maintaining a high level of imaging quality and diagnostic benefit. It can also become very costly. Current government regulations demand unnecessary accuracy in the measurement and performance of certain parameters of x-ray generators whilst ignoring others which are more important. They totally neglect imaging systems. We urge a more critical approach to the requirements for dose and quality control programs. We propose the exchange of information through a user's club and a less regulatory but equally important role for government.

Calibration↗
PubMed1983

Comparison and variations of the speed of radiographic film.

A study of 50 different batches of film from 20 institutions across Ontario was conducted to measure sensitivities when exposed between intensifying screens and to white light. For films of different types but of the same nominal speed, the x-ray exposures required to produce a net optical density of 1.0 varied by a factor of up to 2.5. For films of the same type from different batches, the required exposure varied by +/- 20%. It was found that sensitivity to white light from the commonly used Wejex sensitometer was not always a good indicator of x-ray sensitivity, and therefore should not be used to compare speeds of different films or films from different batches.

Technology, Radiologic↗
PubMed1983

Speeds of film-screen combinations for radiography.

Values of Ex, the exposure required to yield a net optical density of 1.0, were determined for 12 blue- and nine green-sensitive film types used with 11 blue- and eight green-emitting screen types respectively. The measurements were made using x-rays generated at 80 kVp and 200 mA, under conditions simulating clinical procedures. To examine reciprocity law failure many of the determinations were repeated under similar conditions but at 15 mA. The values of Ex obtained at 15 mA were 6% to 93% greater than those at 200 mA.

Radiographic Image Enhancement↗
PubMed1981

Performance evaluation of image-intensifier tubes.

A series of image quality measurements were obtained over a two-year period for eight image-intensifier tube fluoroscopic units used in clinical practice. The measurements were in agreement with a radiologist's opinion of the image quality for each tube. The results showed that some systems did not change significantly over the two-year period, while others deteriorated from acceptable to unacceptable image quality during this time. For this reason, it is recommended that measurements be obtained for all diagnostic fluoroscopic equipment at least semiannually to monitor image quality and remedy any changes before diagnostic accuracy is severely affected.

Fluoroscopy↗
PubMed1979

A head holder for operative serial angiography.

An apparatus was developed to combine two functions--a versatile neurosurgical head clamp and a compact film changer for operative serial angiography. The construction costs were +15,000, and provided a programmer, six cassettes, and attachments to position the film changer over much of the skull surface. Exposures are obtained by a mobile x-ray machine.

Cerebral Angiography↗