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Biomedical subjects

A E Allen

Publications and source records attributed to A E Allen.

At least 19 recordsLinked to original sources
PubMed2001

Diversity and detection of nitrate assimilation genes in marine bacteria.

A PCR approach was used to construct a database of nasA genes (called narB genes in cyanobacteria) and to detect the genetic potential for heterotrophic bacterial nitrate utilization in marine environments. A nasA-specific PCR primer set that could be used to selectively amplify the nasA gene from heterotrophic bacteria was designed. Using seawater DNA extracts obtained from microbial communities in the South Atlantic Bight, the Barents Sea, and the North Pacific Gyre, we PCR amplified and sequenced nasA genes. Our results indicate that several groups of heterotrophic bacterial nasA genes are common and widely distributed in oceanic environments.

Bacteria↗
PubMed2000

Transcriptional autorepression of the stress-inducible gene ATF3.

Previously, we demonstrated that ATF3 (activating transcription factor-3) is a stress-inducible gene, and the protein it encodes is a transcriptional repressor. In this report, we present evidence suggesting that ATF3 represses the transcription of its own gene. Interestingly, efficient repression requires a consensus ATF/cAMP-responsive element site in the promoter and a previously unidentified ATF3-binding site immediately downstream from the TATA box. Although this new site resembles the known ATF/cAMP-responsive element sequences at the flanking sequence, it differs from them at the center key residues. These observations indicate that ATF3 can tolerate variations in the center of the binding sites if the flanking sequences are favorable. The repression of the ATF3 promoter by its own gene product provides a mechanistic explanation, at least in part, for the transient expression pattern of the ATF3 gene upon stress induction.

Activating Transcription Factor 3↗
PubMed1999

ATF3 and stress responses.

The purpose of this review is to discuss ATF3, a member of the ATF/CREB family of transcription factors, and its roles in stress responses. In the introduction, we briefly describe the ATF/CREB family, which contains more than 10 proteins with the basic region-leucine zipper (bZip) DNA binding domain. We summarize their DNA binding and heterodimer formation with other bZip proteins, and discuss the nomenclature of these proteins. Over the years, identical or homologous cDNA clones have been isolated by different laboratories and given different names. We group these proteins into subgroups according to their amino acid similarity; we also list the alternative names for each member, and clarify some potential confusion in the nomenclature of this family of proteins. We then focus on ATF3 and its potential roles in stress responses. We review the evidence that the mRNA level of ATF3 greatly increases when the cells are exposed to stress signals. In animal experiments, the signals include ischemia, ischemia coupled with reperfusion, wounding, axotomy, toxicity, and seizure; in cultured cells, the signals include serum factors, cytokines, genotoxic agents, cell death-inducing agents, and the adenoviral protein E1A. Despite the overwhelming evidence for its induction by stress signals, not much else is known about ATF3. Preliminary results suggest that the JNK/SAPK pathway is involved in the induction of ATF3 by stress signals; in addition, IL-6 and p53 have been demonstrated to be required for the induction of ATF3 under certain conditions. The consequences of inducing ATF3 during stress responses are not clear. Transient transfection and in vitro transcription assays indicate that ATF3 represses transcription as a homodimer; however, ATF3 can activate transcription when coexpressed with its heterodimeric partners or other proteins. Therefore, it is possible that, when induced during stress responses, ATF3 activates some target genes but represses others, depending on the promoter context and cellular context. Even less is understood about the physiological significance of inducing ATF3. We will discuss our preliminary results and some reports by other investigators in this regard.

Activating Transcription Factor 3↗
PubMed1992

Transitional cell papillary bladder neoplasm in a girl: an unusual presentation.

An 8-year-old girl presented with the clinical features of acute appendicitis. The removed appendix was normal but the abdominal pain persisted. There were no urinary symptoms and bacteriological examination of the urine was negative. An ultrasound scan showed an intravesical tumor that was subsequently excised. Histology showed a grade 1 transitional cell papillary bladder carcinoma of low grade malignancy. All previously reported cases have presented with urinary tract symptoms, usually hematuria.

Acute Disease↗
PubMed1991

Cloning of cDNA for the glutamate-binding subunit of an NMDA receptor complex.

The amino acids L-glutamic and L-aspartic acids form the most widespread excitatory transmitter network in mammalian brain. The excitation produced by L-glutamic acid is important in the early development of the nervous system, synaptic plasticity and memory formation, seizures and neuronal degeneration. The receptors activated by L-glutamic acid are a target for therapeutic intervention in neurodegenerative diseases, brain ischaemia and epilepsy. There are two types of receptors for the excitatory amino acids, those that lead to the opening of cation-selective channels and those that activate phospholipase C (ref. 11). The receptors activating ion channels are NMDA (N-methyl-D-aspartate) and kainate/AMPA (alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate)-sensitive receptors. The complementary DNAs for the kainate/AMPA receptor and for the metabotropic receptor have been cloned. We report here on the isolation and characterization of a protein complex of four major proteins that represents an intact complex of the NMDA receptor ion channel and on the cloning of the cDNA for one of the subunits of this receptor complex, the glutamate-binding protein.

Amino Acid Sequence↗
PubMed1991

The effect of environmental photoperiodicity on indole rhythms and locomotor activity in sighted and eye covered chickens.

Direct (via the skull) and indirect (via the eyes) light on the rate of adaptation of circadian rhythms of pineal, retina and serum indoleamines and of locomotor activity was examined by observing photoperiod reversal in eye covered and normally sighted chickens. Eye covering did not affect indoleamine levels nor locomotor activity on the regular light:dark (L:D) cycle. However, following photoperiod reversal, the eye covered chickens showed slower rates of adaptation of retinal melatonin and locomotor activity to the new L:D cycle than did the normal sighted chickens. Pineal and serum indole levels were unaffected by eye covering. Our results in birds indicate that 1) light to the eye has a role in governing retinal melatonin and locomotor activity, 2) the pineal is directly photosensitive, and 3) the endogenous rhythm of pineal melatonin may play a role in the entrainment of the locomotor rhythm in the chicken.

Adaptation, Physiological↗
PubMed1990

Cold stress during scotophase elicited differential responses in quail pineal, retinal, and serum melatonin levels.

Effects of cold stress during scotophase on pineal, retinal and serum melatonin levels were examined in quails. All experimental subjects were housed under a constant room temperature of 23 +/- 2 degrees C and a daily 12 h:12 h light:dark cycle. After 1 week of adaptation, quails were exposed to 4 degrees C in darkness for 60, 120, 180 and 210 min. Immediately following their respective cold treatments, subjects were sacrificed at mid-dark and pineal, retina and serum samples were collected for melatonin radioimmunoassay. Cold stress during scotophase was found to potentiate melatonin levels in the retinas significantly. Conversely, cold exposures in dark significantly decreased melatonin levels in pineal glands and serum. Such diversified responses might be attributed to tissue specific variations in adrenergic and/or dopaminergic receptors responsible for regulating the synthesis and/or secretory mechanisms of melatonin.

Animals↗
PubMed1989

Cold exposure or norepinephrine injections altered melatonin levels in the quail retina.

The possible involvement of ambient temperature and norepinephrine on daytime levels of retinal melatonin were investigated in quails. For a minimum of 1 week, experimental animals were housed under constant room temperature of 23 +/- 2 degrees C and a daily 12:12 h light-dark cycle with light on at 06.00-18.00 h. The quails were then transferred to a cold room of 4 degrees C and cold-exposed for 0, 30, 60, 90 and 120 min. Retina samples were subsequently collected at mid-light for melatonin radioimmunoassay. An initial decline of melatonin was detected in the cold treated birds after 30 min of exposure. Thereafter prolongation of cold stimulation produced significant increases in the levels of retinal melatonin. In the second experiment, intra-peritoneal norepinephrine injections (0, 1, 10 and 100 micrograms/bird) at mid-light were found to increase the levels of retinal melatonin in quails. We postulate the cold-induced increase of retinal melatonin may be attributed to an augmented level of catecholamines released as a general neuroendocrine response to temperature decrements.

Animals↗
PubMed1989

Inherited changes in concentrations of retinal and serum melatonin in the chicken.

Concentrations of melatonin in the retina, serum, and pineal gland were studied in genetically blind chicks carrying an autosomal recessive mutation, rc, characterized by the degeneration of photoreceptors in the retina after hatching. Blind homozygous (rc/rc) and sighted heterozygous (Rc+/rc) chicks were housed under 12:12 light:dark cycles. They were decapitated at 4, 6, 8, and 10 weeks of age at midlight and middark. Retinas, pineal glands, and serum samples were collected, and the resultant tissue melatonin was extracted and determined by radioimmunoassay. Retinal and pineal melatonin were also identified and quantified by gas chromatography-mass spectrometry (GC-MS). Good correlations were demonstrated between the values obtained by GC-MS and levels of quantified by radioimmunoassay. In all the tissues studied, there were age-related changes and diurnal variations in melatonin levels with high levels in the dark period. Melatonin levels in the retina and serum of rc/rc chicks were also significantly lower than those of Rc+/rc control birds. However, storages of melatonin in the pineal gland were similar between the two groups of chicks studied. These results suggest that (1) retinal melatonin is synthesized in the photoreceptor, (2) the phototransduction process which produces neural signals (i.e., electroretinogram) may be different from the phototransduction process which initiated the rhythmic melatonin synthesis and production in the retina, (3) the inherited degeneration of retinal photoreceptors with lower retinal melatonin levels correlates with an inherited abnormality of the pineal melatonin synthesis and/or secretion resulting in lower serum melatonin levels (pleiotropism), (4) levels of pineal melatonin (an indicator of the rate of synthesis and/or storage) and that of serum melatonin (an indicator of the rate of release) may not be directly correlated, and (5) the chicken pineal secretes melatonin not only by simple diffusion but also from a bound pool of melatonin in the gland.

Animals↗
PubMed1988

Neurotensin binds with high affinity to small cell lung cancer cells.

Several small cell lung cancer cell lines bound 125I-neurotensin with high affinity. Radiolabeled neurotensin bound with high affinity (Kd = 4 nM) to a single class of sites (2300/cell) using cell line NCI-H209. Binding was time dependent and reversible. Pharmacology studies indicated that the C-terminal of neurotensin was important for the high affinity binding activity. Because high concentrations of neurotensin and its receptors are associated with small cell lung cancer, neurotensin may function as a regulatory peptide in this disease.

Binding, Competitive↗
PubMed1987

Pineal, retinal, serum melatonin, and N-acetylserotonin rhythms in chicks on reversing light regimen and eye covering.

After reversing a 12:12-h light-dark regimen of environmental lighting, pineal and retinal melatonin levels of white leghorn chicks recorded at the first mid-darkness were greatly enhanced and reached maximum levels after three more days; those recorded during the light periods indicate gradual decline but were far from the nadir of the original light period, even at the end of the experiment. The first mid-darkness serum melatonin levels recorded after photoperiod reversal were not much different from their original mid-light values. However, on continuing with the reversed regimen, the next mid-darkness levels were sharply increased, and maximum levels were reached after a further 2 days. Under the same experimental conditions light had much more drastic effects, and 6 h on the reversed regimen were sufficient to bring down completely the high value of the original mid-darkness period to the level of the starting mid-light nadir. Retinal N-acetylserotonin (NAS) measured simultaneously had a pattern similar to that of melatonin, but the pineal NAS rhythm did invert completely, albeit gradually. Eye covering did not prevent inversion of pineal and serum melatonin rhythms, which were identical in eye-covered and sighted control chicks on the reversed regimen of light. However, retinal melatonin values of the light periods were significantly less depressed in eye-covered than in sighted control chicks. Moreover, eye covering completely prevented the retinal NAS depression under light but did not affect pineal NAS. During darkness retinal and pineal NAS elevation was sluggish in the eye-covered chicks.

Animals↗