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Biomedical subjects

D A Carter

Publications and source records attributed to D A Carter.

At least 37 records · Page 2Linked to original sources
PubMed2000

Cyclical expression of egr-1/NGFI-A in the rat anterior pituitary: a molecular signal for ovulation?

Molecular genetic studies of egr-1/NGFI-A have recently established a key role for this immediate early gene in anterior pituitary development, and particularly in transcriptional regulation of the LH beta-subunit gene. These studies, using null mutant mice, addressed the developmental aspects of gonadotrophin gene regulation by egr-1 and, because of the limitations of this approach, did not address the role of egr-1 in adult reproductive physiology. Using the rat, we have now investigated the expression of egr-1 during the female reproductive cycle, and have found evidence of cyclical changes in anterior pituitary egr-1 expression, at mRNA, protein, and DNA binding activity levels. Specifically, we have shown that egr-1 mRNA is significantly elevated during proestrous, and conversely suppressed on the subsequent day of oestrous. We have also demonstrated significantly raised levels of an approximately 70 kDa Egr-1 immunoreactive protein band during the night of proestrous, together with markedly raised levels of a Egr-1 consensus sequence DNA binding complex. These studies are indicative of both direct egr-1 gene regulation by oestrogen, and also regulation by GnRH. Finally, we have sequenced previously uncharacterized regions of the egr-1 gene and found evidence of a potential oestrogen response element. Our findings are consistent with the hypothesis that Egr-1 forms at least part of the molecular signal for ovulation in the pituitary.

Animals↗
PubMed1999

The detection of nonhybrid, trisomic, and triploid offspring in sexual progeny of a mating of Phytophthora infestans.

Eighty single-oospore offspring of Phytophthora infestans from a mating of isolates, which had previously been analyzed for segregation of avirulence/virulence, were assessed for the inheritance of 20 RFLP markers. Three offspring were triploid; they inherited three alleles at all loci where this could be detected and when heterozygous, showed unequal intensities of hybridization with most probes. Twenty-four offspring were trisomic, as each had three doses of one or a few markers, evident from their inheritance of three alleles or from unequal hybridization to one probe. Coinheritance of the extra allele(s) and mitochondrial haplotype in the majority of trisomic offspring suggested that meiosis in oogonia was more aberrant than in antheridia. Linkage analysis was performed on 50 offspring, which were assumed to be euploid; six small linkage groups were detected and several avirulence loci were found to be linked. The origins of aberrant offspring are discussed.

Blotting, Southern↗
PubMed1999

Presence of alpha and a mating types in environmental and clinical collections of Cryptococcus neoformans var. gattii strains from Australia.

Cryptococcus neoformans var. gattii lives in association with certain species of eucalyptus trees and is a causative agent of cryptococcosis. It exists as two mating types, MATalpha and MATa, which is determined by a single-locus, two-allele system. In the closely related C. neoformans var. neoformans, the alpha mating type has been found to outnumber its a counterpart by at least 30:1, but there have been very limited data on the proportions of each mating type in C. neoformans var. gattii. In the present study, specific PCR primers were designed to amplify two separate alpha-mating-type genes from C. neoformans var. gattii strains. These were used to survey for the presence of the two mating types in clinical and environmental collections of C. neoformans var. gattii strains from Australia. Sixty-eight of 69 clinical isolates produced both alpha mating type-specific bands and were assumed to be of the alpha mating type. The majority of environmental isolates were also of the alpha mating type, but the a mating type was located in two separate areas. In one area, the a mating type outnumbered the alpha mating type by 27:2, but in the second area, the ratio of the two mating types was close to the 50:50 ratio expected for sexual recombination.

Animals↗
PubMed1999

Accuracy of magnetic resonance imaging stereotactic coordinates with the cosman-roberts-wells frame.

Quality assessment on the accuracy of a Cosman-Roberts-Wells (CRW) magnetic resonance imaging (MRI) stereotactic ring which had nonferrous stainless steel screws and positioning posts and a localizer with petroleum jelly in the fiducials, purchased in 1994, revealed errors of greater than 4 mm with targets in phantoms. Image fusion of objects within the phantom indicated the central area was accurately depicted by CT or MRI. We then tested a newer CRW- MRI ring (MRIA-IHR with titanium screws and posts) and localizer (MRIA-2-LF with fiducials filled with copper sulfate) and found that the MRI stereotactically calculated target coordinates matched both the known position of these targets in the phantom as well as the CT stereotactically calculated coordinates within approximately 1 mm. We also describe excellent superimposition of CT and MRI stereotactically determined surfaces in a recent clinical case using the new hardware. This shows that recent modifications to the CRW-MRI stereotactic system can make it accurate for small targets, but we emphasize that all systems need to undergo ongoing local quality assessment to ensure acceptable accuracy in practice.

Brain↗
PubMed1998

Expression of a novel rat protein tyrosine phosphatase gene.

The cDNA sequence and expression of a novel rat protein tyrosine phosphatase (PTP) gene is reported. The predicted amino acid sequence is similar to rat PRL-1, but is more closely related to human PTP4A, another member of the recently identified fourth group of PTPs. Therefore, multiple PTPs of this group are expressed in mammalian species. The novel rat PTP gene is expressed in the anterior pituitary gland in a sexually dimorphic pattern which is indicative of a specialized role in endocrine function.

Adrenal Glands↗
PubMed1998

Regulation of the synthesis and secretion of vasopressin.

We have developed a transgenic system that, for the first time, facilitates the monitoring of the regulatory dynamics of a central peptidergic system from transcription of a neuropeptide gene to the storage and release of the mature secretory product. Here we describe novel studies on the regulation of this system by physiological stimuli. The rat hypothalamic vasopressin (VP) mRNA responds in two ways to the functional demand imposed by an osmotic challenge. Firstly, the abundance of the VP RNA increases, and secondly, the size of the VP transcript increases as a consequence of a lengthening of the poly(A) tail. We have previously shown that chronic ingestion of 6-n-propyl-2-thiouracil (PTU), while not affecting plasma osmolality or VP mRNA size, results in a significant increase in the abundance of the hypothalamic VP mRNA. We now show that chronic PTU ingestion results in a dramatic increase in the abundance of the mRNA encoded by a modified rat vasopressin transgene that is expressed in rat vasopressinergic magnocellular neurons. This is accompanied by a significant depletion in neural lobe stores of a VP. However, this increase in transgene expression is accompanied by an increase in the proportion of transgene encoded products reaching the neural lobe--the pituitary content of a unique peptide encoded by the modified transgene does not change. These observations are further evidence in support of models of neurohypophyseal homeostasis that suggest that pituitary VP peptide levels passively reflect changes in hormone release and synthesis and that the availability of mRNA is the primary determinant of pituitary VP content in the basal state.

Animals↗
PubMed1998

Regenerated retinal ganglion cell axons form normal numbers of boutons but fail to expand their arbors in the superior colliculus.

Regenerated retinal ganglion cell (RGC) axons can re-form functional synapses with target neurons in the superior colliculus (SC). Because preterminal axon branching determines the size, shape and density of innervation fields, we investigated the branching patterns and bouton formation of individual RGC axons that had regrown along peripheral nerve (PN) grafts to the SC. Within the superficial layers of the SC, the regenerated axons formed terminal arbors with average numbers of terminal boutons that were similar to the controls. However, axonal branches were shorter than normal so that the mean area of the regenerated arbors was nearly one-tenth that of control arbors and the resulting fields of innervation contained greater than normal numbers of synapses concentrated in small areas of the target. Our results have delineated a critical defect in the reconstitution of retino-collicular circuitry in adult mammals: the failure of terminal RGC branches to expand appropriately. Because recent studies have documented that brain-derived neurotrophic factor (BDNF) can specifically lengthen RGC axonal branches not only during development in the SC but also within the adult retina after axotomy, the present quantitative studies should facilitate experimental attempts to correct this deficit of the regenerative response.

Animals↗
PubMed1998

Cost-efficient localization of seizures of mesiotemporal onset with foramen-ovale electrodes.

Foramen ovale (FO) electrodes can identify mesiotemporal lobe (MTL) seizure onsets but are infrequently used in the USA. Ten patients with presumed MTL ictal onset, unlocalized noninvasively, had FO electrodes inserted during long term monitoring for epilepsy. Placement was facilitated by intraoperative use of oblique submental and modified Caldwell view fluoroscopy. Eighty percent of patients had ictal localization by FO electrodes. This led to anterior temporal lobectomy in six with 83% being seizure free after follow-up of 20-32 months. The mean total costs of placing these electrodes was approximately half that of subdural strips and a quarter that of depth electrodes. Foramen ovale electrodes represent a cost-effective and efficient method of seizure localization when noninvasive workup suggests but is not definitive for MTL origin.

Cost-Benefit Analysis↗
PubMed1998

Basal skull fracture with traumatic polycranial neuropathy and occluded left carotid artery: significance of fractures along the course of the carotid artery.

A patient who survived with traumatic multiple cranial nerve palsies and occluded internal carotid artery associated with a basal skull fracture that involved the carotid canal is described. A literature review indicates that a wide variety of injuries can occur to the carotid artery as it passes through a fractured skull base. Basal fractures involving the course of the carotid artery reflect a significant risk of carotid injury.

Accidents, Traffic↗
PubMed1997

Modulation of cellular AP-1 DNA binding activity by heat shock proteins.

Recent studies have indicated that ubiquitously expressed molecular chaperones of the heat shock protein (Hsp) class may have an additional, nuclear, role in the regulation of gene expression. Experiments on cellular transcription factors derived from the rat adrenal gland have now shown that Hsps modulate in vitro DNA binding activity of the AP-1 factor. Both Hsc70 (p73) and Hsp70 (p72) were demonstrated to exert this effect through a mechanism that appears to be independent of both redox, and phosphorylation state. Further studies on the effect of Hsps on recombinant Fos/Jun protein binding activity indicated that the mechanism of action involves a selective attenuation of high affinity c-Fos:c-Jun binding as compared with c-Jun homodimer binding activity. Because cellular and physiological stress are associated with the induction of both AP-1 and Hsps it is apparent that Hsps may play a modulatory role in the regulation of AP-1 responsive genes.

Animals↗
PubMed1997

Transcription of the vasoactive intestinal peptide gene in response to glucocorticoids: differential regulation of alternative transcripts is modulated by a labile protein in rat anterior pituitary.

Expression of the vasoactive intestinal peptide (VIP) gene is controlled by glucocorticoids in a tissue- and endocrine status-specific manner. We have investigated the molecular mechanisms that determine glucocorticoid regulation of VIP gene expression in the rat pituitary. In initial experiments, using explant cultures of rat pituitary glands, we have demonstrated that treatment with the glucocorticoid agonist dexamethasone leads to a marked increase in VIP mRNA levels. This effect was found to be selective for the larger of two alternatively polyadenylated VIP transcripts, and in addition, protein synthesis inhibitors markedly enhanced the magnitude of this response indicating that a labile pituitary protein acts to attenuate the transcript-selective response to glucocorticoids. Nuclear run-on analysis of transcription demonstrated that the effects of dexamethasone in vitro are mediated largely, if not completely, at the level of transcription. In order to investigate the role of VIP promoter sequence in the glucocorticoid response, we then demonstrated that the activity of rat VIP gene promoter/reporter constructs in GH3 pituitary cells are up-regulated by dexamethasone. This up-regulation is virtually abolished following removal of promoter sequence between -162 and -89 of the start of transcription. Using an in vitro electrophoretic mobility shift assay, we have also demonstrated that this region of the promoter binds recombinant glucocorticoid receptor protein. The results of our study therefore indicate a direct mechanism of action for the modulation of VIP gene expression by glucocorticoids, and furthermore provide evidence of a mechanism that permits selective glucocorticoid regulation of alternative VIP transcripts.

Animals↗
PubMed1997

A set of electrophoretic molecular markers for strain typing and population genetic studies of Histoplasma capsulatum.

A set of eleven biallelic and three multiallelic molecular markers have been developed to analyze populations of Histoplasma capsulatum. All markers are amplified by polymerase chain reaction (PCR) and can be readily scored using minimal amounts of template DNA. The 11 biallelic loci have polymorphic restriction endonuclease sites or small insertions or deletions which may be assessed by agarose gel electrophoresis. These markers are inherited in an unambiguous manner and are ideal for assessing structure and gene flow within US populations of H. capsulatum, but are monomorphic in non-US populations. Both length and sequence variation are present in the multiallelic loci, which can be scored by direct sequencing, polyacrylamide gel electrophoresis, or single-strand conformation polymorphism (SSCP): As they are hypervariable, the multiallelic loci can be used to type isolates and to assess the level of genetic variation within populations. Preliminary results indicate that the three multiallelic markers presented are sufficient to distinguish isolates at the individual level and are polymorphic in both US and non-US populations. This collection of molecular markers will be a useful tool in population and epidemiology studies of H. capsulatum.

Alleles↗
PubMed1997

Analysis of the internal transcribed spacer regions of ribosomal DNA in common airborne allergenic fungi.

Ribosomal DNA internal transcribed spacer (ITS) sequences were investigated in the genera Alternaria, Aspergillus, Cladosporium and Penicillium, to identify regions suitable for the design of genus- and species-specific oligonucleotide probes. The ITS regions of all four genera were quite distinct. However, we discovered that the genera Aspergillus and Penicillium displayed high similarity in most of the ITS2 region. Whilst interspecies similarity within Alternaria and Cladosporium was high in both ITS regions 1 and 2, ITS1 similarity within Aspergillus and Penicillium was lower by comparison. We conclude that: (1) the ITS2 region is highly conserved between Aspergillus and Penicillium, and (2) the ITS1 region will allow for the development of specific probes to distinguish between Aspergillus and Penicillium.

Alternaria↗
PubMed1997

Retino-geniculate axons regenerating in adult hamsters are able to form morphologically distinct terminals.

Adult mammalian retinal ganglion cells (RGCs) can regenerate through peripheral nerve (PN) grafts and innervate central nervous system (CNS) targets. Previous studies have demonstrated a basic level of differentiation of such projections. To further assess the specificity and functionality of regenerated CNS connections we have developed a new model in which RGCs are directed through a PN graft into the dorsolateral geniculate body (LGBd) while preserving the visual cortex and radiations. We also describe by light microscopy that regenerating RGC axons which enter the LGBd differentiate and form subtypes of RGC terminals reminiscent of those seen in the normal LGBd. Thus the adult CNS contains cues that permit phenotypic differentiation of terminal types during regeneration.

Animals↗
PubMed1997

Molecular markers reveal differentiation among isolates of Coccidioides immitis from California, Arizona and Texas.

Coccidioides immitis causes coccidioidomycosis, a fungal disease of both immuno-compromised and otherwise healthy people; it is capable of causing large epidemics and the disease is often refractory to chemotherapy. To quantify the magnitude of population differentiation and estimate levels of gene flow in C. immitis, multilocus genotypes were scored for 20-25 clinical isolates from each of Bakersfield (California), Tucson (Arizona), and San Antonio (Texas). The molecular markers used were PCR products with polymorphic restriction endonuclease sites, found and characterized in a previous study of the Tucson population. The data show very highly significant differences in allele frequencies between all three populations, and suggest very low levels of migration between populations. One isolate in the San Antonio sample was an outlier, showing the California-specific allele at all four of the loci distinguishing the two populations, and subsequent inquiries indicated that the infection had indeed been acquired in California. Thus, genetic information can be used to infer the geographical origin of a fungal infection.

Arizona↗