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D A Carter

Publications and source records attributed to D A Carter.

At least 55 records · Page 3Linked to original sources
PubMed1997

cAMP response element-binding protein phosphorylation and DNA binding activity are increased in the anterior pituitary gland following glucocorticoid depletion.

Activation of the hypothalamo-pituitary-adrenal (HPA) axis during stress is associated with increased expression of genes that code for regulatory hormones such as corticotrophin-releasing factor (CRF) and ACTH. The identity of the transcription factors that mediate these changes in gene expression is not known. In the present study we have investigated the expression of the cAMP response-element binding protein (CREB) in mouse pituitary, and its regulation during a pharmacological paradigm that simulates activation of the CRF-ACTH axis. Using Western blots and DNA binding assays we have shown that both CREB protein (43 kDa) and CRE binding exhibit a readily-detectable basal level of activity in the pituitary. Following treatment with the 11 beta-hydroxylase inhibitor metyrapone, CRE binding activity was increased at 1 and 2 h but levels of CREB protein were not found to be consistently elevated. However, using a Ser133 phosphopeptide-specific antibody, that detects the functionally important phosphorylated form of CREB (P-CREB), we have shown that levels of pituitary P-CREB are markedly elevated following metyrapone. The same antibody was also used in DNA binding assays, and in the presence of this antiserum CRE binding activity in samples extracted from metyrapone-treated animals was reduced to levels similar to controls. Parallel experiments have confirmed previous studies showing increases in c-Fos expression and AP-1 DNA binding activity following metyrapone treatment but we have shown that c-Fos-associated binding activity does not appear to contribute to the increase in activity detected using the CRE binding probe. Our evidence of functionally relevant changes in pituitary CREB activity following glucocorticoid depletion must be viewed in the context of numerous other novel pituitary transcription factors that are implicated in HPA regulation, but our use of mice as an experimental model has facilitated the use of novel mouse mutants that can be used to dissect the role of individual factors.

Animals↗
PubMed1996

Circadian rhythms and autoregulatory transcription loops--going round in circles?

Recent advances in the molecular analysis of biological timing have appeared to bring us closer to an answer to the 'big question', namely, 'What is the timing mechanism that enables an organism to measure the circadian (around 24 h) period?'. In this minireview, we consider the validity of the fashionable concept that autoregulatory feedback loops, centered on transcription, form the basis of the clock, and we offer a fresh view of recent progress as it relates to mammalian systems.

Animals↗
PubMed1996

Trans-synaptic control of NGFI-A and jun-B expression: contrasting transcriptional and post-transcriptional mechanisms directed by common receptors.

Previous studies have demonstrated that of the multiple primary response gene products which are induced in the rat pineal gland through a nocturnally activated adrenoceptor-linked mechanism. JunB is the principal component of a dark phase-specific activator protein-1 DNA binding complex. JunB is therefore implicated as a nuclear component of the mechanisms that determine nocturnal changes in pineal function. It is now shown that the marked increase in jun-B mRNA expression following norepinephrine stimulation in vitro, is mediated through a post-transcriptional mechanism that involves mRNA stabilization. This mode of regulation is contrasted with that controlling the expression of other primary response genes. In the case of NGFI-A, a co-regulated primary response gene which is controlled through a pharmacologically similar pathway, nuclear run-on transcription assays have shown that pineal mRNA levels are elevated through an increase in transcription rate that can be measured both in vitro and in vivo. These results show that multiple molecular mechanisms are engaged to effect the genomic consequences of adrenoceptor stimulation, and that rhythmic changes in gene expression may be controlled by post-transcriptional mechanisms involving mRNA stability.

Adrenergic Agents↗
PubMed1996

Molecular markers reveal cryptic sex in the human pathogen Coccidioides immitis.

Coccidioides immitis, cause of a recent epidemic of "Valley fever" in California, is typical of many eukaryotic microbes in that mating and meiosis have yet to be reported, but it is not clear whether sex is truly absent or just cryptic. To find out, we have undertaken a population genetic study using PCR amplification, screening for single-strand conformation polymorphisms, and direct DNA sequencing to find molecular markers with nucleotide-level resolution. Both population genetic and phylogenetic analyses indicate that C. immitis is almost completely recombining. To our knowledge, this study is the first to find molecular evidence for recombination in a fungus for which no sexual stage has yet been described. These results motivate a directed search for mating and meiosis and illustrate the utility of single-strand conformation polymorphism and sequencing with arbitrary primer pairs in molecular population genetics.

Base Sequence↗
PubMed1996

Reversal of CNS-prophylaxis-related leukoencephalopathy after CSF shunting: case histories of identical twins.

We report the case histories of identical twin brothers who developed concordant acute lymphoblastic leukemia at the age of 4 years and who later developed leukoencephalopathy and hydrocephalus related to central nervous system prophylaxis by, in the first case intrathecally administered methotrexate and, in the second by intrathecally administered methotrexate and cranial irradiation. The delayed encephalopathy developed 9 and 22 months respectively after the first dose of intrathecal methotrexate. Both patients underwent cerebrospinal fluid shunting mainly for their hydrocephalus. The imaging studies have shown that both hydrocephalus and leukoencephalopathy have improved significantly after ventriculoperitoneal shunt insertion. We review the pathophysiology of prophylaxis-related encephalopathy in leukemia patients and summarize its clinical, histological, and radiological characteristics. We also discuss the possible contribution of altered cerebrospinal fluid dynamics in the development of leukoencephalopathy.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed1996

Spinal subdural haematoma as a complication of immediate epidural blood patch.

PURPOSE: The authors report a case of a patient who developed spinal subdural haematoma after a series of epidural blood patches to alert anaesthetists to this rare complication. CLINICAL FEATURES: The patient was a 35-yr-old woman without coagulopathy and was initially treated elsewhere for chronic pain by repetitive epidural phenol injections. When the dura was inadvertently punctured during subsequent attempts to inject phenol, immediate epidural blood patch was performed to treat or prevent headache. The patient developed cauda equina syndrome after six epidural blood patches. The clinical diagnosis was confirmed by magnetic resonance imaging and the intradural haematoma was evacuated surgically. The patient made a complete recovery. CONCLUSIONS: Epidural blood patch is not without complications. Transient backache and/or radiculopathy may occur in up to one-third of patients receiving a blood patch. If signs and symptoms continue or worsen, a spinal subarachnoid and/or subdural haematoma should be suspected and neurosurgical opinion sought. The technique used to identify the epidural space is important in preventing subdural injection of blood. The needle should be withdrawn after dural puncture and the epidural space identified at a different level. Blood patches may carry a higher risk of serious complications after multiple epidural phenol injections because of fibrosis and obliteration of the epidural space. Magnetic resonance scans reliably demonstrate the extent of the pathology. If diagnosed and treated before irreversible changes occur, spinal intradural haematoma can result in complete recovery.

Adult↗
PubMed1996

Ectopic vasopressin expression in MMTV-v-Ha-ras transgenic mice delays the onset of mammary tumorigenesis.

Neuropeptides are often ectopically expressed by non-endocrine tumours. We used transgenic mice to assess the effect of ectopic expression of the neuropeptide, vasopressin, in mammary tumours induced by the transgenetic expression of an activated ras oncogene. Mice bearing a mouse mammary tumour virus-vasopressin (MMTV-VP) fusion transgene synthesise authentic VP in mammary ducts and alveoli. Bitransgenic mice bearing both MMTV-VP and MMTV-v-Ha-ras transgenes developed tumours that were histologically indistinguishable from those of single MMTV-v-Ha-ras animals. However, tumour onset was significantly delayed in the bitransgenic animals. These data provide evidence that an ectopic neuropeptide can slow the development of ras tumours in vivo.

Animals↗
PubMed1996

RNAs encoded by a 3.5-kb bovine vasopressin gene construct are targeted to the neurohypophysis of transgenic mice.

Recent studies have established that the RNA coding for the neuropeptide arginine-vasopressin (AVP) is expressed in the neurohypophyseal compartment of the hypothalamo-neurohypophyseal system. In order to determine the molecular mechanisms that direct this novel expression pattern we have now investigated whether an AVP transgene is similarly regulated. Using a reverse transcriptase-polymerase chain reaction (RT-PCR) approach that permits simultaneous analysis of both endogenous and transgene RNA levels, we have demonstrated that RNA derived from a 3.5-kb bovine vasopressin transgene is expressed in the neurohypophysis of transgenic mice, and is up-regulated by a physiological stimulus (salt-loading) in a similar manner to mouse AVP RNA. Sequences conserved between this region of the murine and bovine AVP genes are therefore sufficient to mediate neurohypophyseal expression. These lines of transgenic mice will serve as a model for the delineation of sequences that target expression beyond the neuronal perikaryon.

Animals↗
PubMed1996

In situ hybridization analysis of vasopressin mRNA expression in the mouse hypothalamus: diurnal variation in the suprachiasmatic nucleus.

The distribution, and diurnal variation of AVP mRNA-expressing neurons in the hypothalamus of the mouse has been investigated using in situ hybridization histochemistry. In general, cells hybridizing with an AVP mRNA-specific oligonucleotide probe in the mouse hypothalamus exhibit a similar distribution to the well-characterized distribution of AVP nuclei in the rat, but species-specific patterns of expression have been observed, a finding that confirms the results of earlier immunocytochemical studies. For example, prominent groups of AVP mRNA expressing cells are found in the region between the paraventricular (PVN) and suprachiasmatic (SCN) nuclei, forming the distinct mouse accessory nucleus, and a periventricular group that merges with the PVN neurons. Sampling of brains during both phases of the daily cycle (either 10.00 h (light) or 22.00 h (dark)) revealed a marked and significant variation in AVP mRNA abundance in the SCN whereas a similar variation was not consistently observed in the magnocellular neurons of the supraoptic nucleus (SON). This study has confirmed the distribution of AVP-synthesizing neurons in the mouse hypothalamus, and provided an anatomical substrate for molecular genetic studies in this species that are designed to investigate the basis of neuronal rhythmicity.

Animals↗
PubMed1996

Clinical isolates of Histoplasma capsulatum from Indianapolis, Indiana, have a recombining population structure.

A sample of 30 clinical isolates of Histoplasma capsulatum was analyzed to determine (i) whether genetic exchange is important in the life cycle of this fungus and (ii) whether distinct subpopulations which correlate with disease severity or host immune status exist. Eleven biallelic molecular markers were developed, with the frequency of the least common allele at each molecular locus ranging from 10 to 50%. Every isolate had a different, unique multilocus genotype. Data analysis indicated that frequent recombination occurs within the Indianapolis, Ind., population. There were no associations between isolates from the immunocompromised population or from those with different clinical manifestations of histoplasmosis.

Genes, Fungal↗
PubMed1995

Bovine oxytocin transgenes in mice. Hypothalamic expression, physiological regulation, and interactions with the vasopressin gene.

To gain insights into the molecular mechanisms that restrict the expression of the oxytocin gene to anatomically defined groups of neurons in the hypothalamus, we generated transgenic mice bearing bovine oxytocin genomic fragments. Appropriate neuron-specific and physiological regulation was observed in mice bearing transgene bOT3.5, which consists of the oxytocin structural gene flanked by 0.6 kilobase pair (kbp) of upstream and 1.9 kbp of downstream sequences. bOT3.5 is expressed in oxytocin magnocellular neurons in the mouse supraoptic nucleus and paraventricular nucleus, but transgene RNAs are excluded from vasopressin neurons. Replacement of the drinking diet of the transgenic mice with 2% (w/v) NaCl for 7 days significantly increased the abundance of bovine oxytocin transcripts in the supraoptic nucleus, but not in the paraventricular nucleus, in parallel with the endogenous mouse oxytocin RNA. Surprisingly, mimicry of the endogenous oxytocin gene expression pattern was lost with larger transgenes. Addition of 0.7 kbp of contiguous downstream sequences (transgene bOT) or linkage to the bovine vasopressin gene (transgene VP-B/bOT3.5) repressed hypothalamic expression. No mice were derived bearing transgene bOT6.4, which consists of the oxytocin structural gene flanked by 3 kbp of upstream and 2.6 kbp of downstream sequences, suggesting that the presence of this DNA is detrimental to normal embryonic development. These data suggest that while bOT3.5 contains sufficient cis-acting sequences to mediate expression to particular subsets of hypothalamic neurons, the overall regulation of the oxytocin gene is governed by multiple interacting enhancers and repressors.

Animals↗
PubMed1995

Extradural tumor causing spinal cord compression in Klippel-Trenaunay-Weber syndrome.

BACKGROUND: Myelopathy in Klippel-Trenaunay-Weber syndrome is uncommon but has been reported secondary to spinal vascular malformations. REPORT: A patient with Klippel-Trenaunay-Weber syndrome who presented with spinal cord compression from a spinal extradural mass lesion (angiomyolipoma) is described. DISCUSSION: This association has not been reported previously but is consistent with the segmental vascular abnormalities observed in Klippel-Trenaunay-Weber syndrome.

Adult↗
PubMed1995

Estradiol induces vasoactive intestinal peptide and prolactin gene expression in the rat anterior pituitary independently of plasma prolactin levels.

It is well established that estrogens are potent stimulators of prolactin (PRL) secretion. It has also been demonstrated that estradiol (E2) can increase the expression and the anterior pituitary levels of the vasoactive intestinal peptide (VIP), a peptide which also acts as a potent PRL-releasing factor. It thus remained unknown whether the effects on pituitary VIP were due to E2 itself or to E2-induced hyperprolactinemia (HPRL). In order to test this hypothesis, various plasma PRL levels were induced in rats either with ectopic pituitary grafts, PRL secreting tumours or E2 implants, and VIP mRNA expression in the anterior pituitary was measured by in situ hybridization and Northern blot analyses. Whereas decreases in VIP mRNA can be observed in pituitaries of rats with pure HPRL, a 6-fold increase in VIP mRNA can be seen in E2-treated rats. E2 increased both 1.0 and 1.7 Kb VIP mRNA species. The presence of the graft in E2-treated rats significantly reduced the increase in VIPmRNA observed following E2. The direct stimulation by E2 of VIP mRNA expression was further demonstrated by the fact that statistical analysis of the data indicated that both E2 and graft were acting independently of each other, and that a new selective antiestrogen, RU 58668, almost totally blocked the effect of E2. Moreover, under similar experimental conditions, pituitary PRL mRNA levels were reduced in the graft group and a marked up-regulation was observed similarly in both E2 and in E2 rats bearing ectopic grafts.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

Leukaemia inhibitory factor expression in cultured rat anterior pituitary is regulated by glucocorticoids.

Leukaemia inhibitory factor (LIF) is the generally recognized nomenclature for a pleiotropic cytokine that exerts multiple biological effects in different systems. However, its role in the neuroendocrine system is relatively unexplored, with the exception of one report indicating that LIF may act to determine the unique vascular organization of the pituitary gland. In the present study the expression of LIF mRNA has been demonstrated for the first time in the pituitary gland of the rat, in all three pituitary lobes. However, LIF gene expression is restricted to tissues in explant culture where LIF transcripts are readily detectable by Northern Techniques. Similar studies using the reverse transcriptase-polymerase chain reaction (RT-PCR) technique also failed to detect LIF transcripts in fresh tissue from adult animals. These results are consistent with the hypothesis that LIF acts to mediate the response to trauma, a response that may include the induction of neuropeptide expression in the anterior pituitary. In further studies it has also been shown that anterior pituitary LIF mRNA is super-induced in the presence of protein synthesis inhibitors, a response that indicates a role for a labile protein in the attenuation of LIF expression. Both the explantation response, and the response to protein synthesis inhibitory drugs are decreased in the presence of dexamethasone indicating that a glucocorticoid receptor mechanism acts as a general modulatory influence on LIF mRNA levels. These findings are consistent with the presence of multiple regulatory controls on the expression of LIF that serve to restrict its expression to pathological conditions, and indicate that LIF does not participate in normal endocrine physiology.

Animals↗
PubMed1995

Immunoreactive insulin in rat salivary glands and its dependence on age and serum insulin levels.

The major salivary glands of adult rodents contain immunoreactive insulin (IRI). To determine if the concentration of IRI in salivary glands is modulated by the level of serum insulin, insulin immunoreactivity in the parotid and submandibular glands of male rats at different ages (sucklings, pubescent, mature, and elderly) was assayed and compared with corresponding serum insulin concentrations. Salivary glands from suckling rats contained 94 ng/g (wet weight) insulin, which is 1.6 times higher than the level in pubescent rats, and about 10 times higher than levels in mature and elderly rats. No direct relationship between salivary gland content and serum IRI levels was indicated by the data. In an attempt to increase insulin levels in serum, insulin-secreting pancreatic islet adenomas were induced in young male rats by injecting streptozotocin (an islet tumor-inducing drug) with nicotinamide (which reduces the drug's beta-cell cytotoxicity). The mean insulin content of salivary glands from drug-treated rats that had not yet expressed tumors was no higher than controls. After the development of visible tumors of pancreatic islet tissue, however, salivary gland IRI was markedly elevated, reaching 40 times control levels, whereas serum insulin, and the immunoreactive insulin content of two insulin-sensitive tissues (vis. hepatic, adipose), were elevated only 2-fold. Examination of histologic sections of the parotid and submandibular glands from drug-treated animals revealed no evidence for the formation of salivary tumors. The data indicate that salivary gland insulin content (i) is age-related, being highest in neonates and declining thereafter, (ii) is generally identical in parotid and submandibular glands at a given age, and (iii) is not modulated solely by the animal's serum insulin concentration. These results are discussed in regard to the possible sources of insulin detected in the major salivary glands.

Adenoma, Islet Cell↗
PubMed1994

Ectopic vasopressin expression in MMTV-Wnt-1 transgenic mice modifies mammary tumor differentiation and pathology.

A transgenic mouse model has been developed to test the involvement of ectopic neuropeptide production as a secondary factor in cancer. Mice bearing a mouse mammary tumor virus-vasopressin (MMTV-VP) fusion transgene synthesized authentic vasopressin in mammary ducts and alveoli, but this had no effect on mammary gland development and growth. Mice bearing the MMTV-VP transgene were then mated with mice bearing the MMTV-Wnt-1 transgene to produce bitransgenic animals. Two types of mammary tumor develop in MMTV-Wnt-1 mice; type A mammary adenocarcinomas are uniform with fine acinar structure composed of small epithelial cells arranged to form round cavities and elongated tubules, while adenocarcinoma type B tumors have acinar areas, cystic spaces filled with blood or fluid, intracystic papillary projections, and cords as well as sheets of cells. Compared to the MMTV-Wnt-1 mice, the bitransgenic animals developed proportionally less type B tumors. Further, type B mammary adenocarcinomas from bitransgenic mice exhibited increased proliferation and growth, as judged by mitotic index and argyrophilic nucleolar organizer region counts, compared to type B tumors from MMTV-Wnt-1 mice. These data provide evidence that ectopic neuropeptide production can modulate the development of tumors in vivo.

Adenocarcinoma↗
PubMed1994

A testis-specific promoter in the rat vasopressin gene.

In the rat testis, the vasopressin gene is transcribed into precursor RNAs that are processed into a number of mature transcripts. One of these transcripts has a structure identical to that of the hypothalamic RNA that encodes the vasopressin prepropeptide, but is present at such low levels that it can only be detected by the polymerase chain reaction. Other vasopressin-like RNAs are derived from differential splicing events that join transcribed sequences between 3 and 9 kilobases upstream of the hypothalamic transcription start site to exons corresponding to II and III of the hypothalamic-type RNA. Here we describe the sequence of a testis-specific promoter and the exon structure of its transcription unit. We show that an in vitro synthesized RNA corresponding to the longer testicular vasopressin gene-derived transcript is not able to act as a template for protein synthesis in two different cell-free lysates. As attempts to localize the vasopressin-gene derived RNAs to particular cell types in the testis by in situ hybridization have consistently failed, we have used indirect methods. Three different procedures were used to effect germ cell depletion in adult male rats. Acute heat treatment of the testis, chronic ingestion of hydroxyurea, and chronic vitamin A deficiency all reduced the level of the aberrant testicular vasopressin-gene derived RNAs, indicating that their expression is closely associated with the integrity of germ cells and ongoing spermatogenesis.

Animals↗