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Biomedical subjects

D Melton

Publications and source records attributed to D Melton.

12 recordsLinked to original sources
PubMed2001

Induction of pancreatic differentiation by signals from blood vessels.

Blood vessels supply developing organs with metabolic sustenance. Here, we demonstrate a role for blood vessels as a source of developmental signals during pancreatic organogenesis. In vitro experiments with embryonic mouse tissues demonstrate that blood vessel endothelium induces insulin expression in isolated endoderm. Removal of the dorsal aorta in Xenopus laevis embryos results in the failure of insulin expression in vivo. Furthermore, using transgenic mice, we show that ectopic vascularization in the posterior foregut leads to ectopic insulin expression and islet hyperplasia. These results indicate that vessels not only provide metabolic sustenance, but also provide inductive signals for organ development.

Animals↗
PubMed2000

A single amino acid alteration in murine PrP dramatically alters TSE incubation time.

In order to investigate mutations linked to human TSEs, we have used the technique of gene targeting to introduce specific mutations into the endogenous murine PrP gene which resulted in a P101L substitution (Prnp(a101L)) in the murine PrP gene. This mutation is equivalent to the 102L mutation in the human PrP gene which is associated with Gerstmann-Sträussler syndrome. Since the mutated gene is in the correct chromosomal location and control of the mutant gene expression is identical to that of the wild type murine PrP gene, the precise effect of the 101L mutation in the uninfected and TSE infected mouse can be investigated in this transgenic model. Mice homozygous for this mutation (101LL) while showing no spontaneous TSE disease were more susceptible to TSE disease than wild type mice following inoculation with GSS infectivity. Disease was transmitted from these mice to mice both with and without the Prnp(a101L) allele. The 101L mutation does not therefore produce spontaneous genetic disease in mice but does dramatically alter incubation periods following TSE infection. Additionally, a rapid TSE transmission was demonstrated associated with extremely low amounts of PrP(Sc).

Amino Acid Substitution↗
PubMed1997

Laparoscopy in the evaluation and treatment of patients with AIDS and acute abdominal complaints.

BACKGROUND: The evaluation of AIDS patients with acute abdominal complaints (AAC) is quite difficult, and surgical intervention is associated with a high complication rate. The intent of this study is to evaluate the application of laparoscopy in the diagnosis and treatment of AIDS patients with AAC. METHODS: This is a retrospective analysis of 10 consecutive AIDS patients who presented with AAC. Each had evaluation by a surgical team with subsequent laparoscopic intervention. The charts were reviewed for age, sex, time with AIDS, AIDS comorbidities, evaluation modalities, findings, treatment modalities, and outcome. RESULTS: Laparoscopy resulted in the successful surgical treatment of four patients, diagnosis of medically treatable conditions in four patients, and alteration of the incision site in the remaining two patients. Each patient thus received direct benefit from laparoscopy. Two complications, in the converted patients, and no mortalities were encountered. CONCLUSIONS: Laparoscopy is a safe and effective interventional modality in the diagnosis and treatment of AAC in the AIDS patient.

Abdomen, Acute↗
PubMed1997

Vertebrate neural induction.

During early vertebrate development, the cells of the ectoderm choose between two possible fates: neural and epidermal. The process of neural induction was discovered nearly 70 years ago in vertebrates, and molecular analyses in recent years using Xenopus laevis embryos have identified several secreted factors with direct neural-inducing ability. There is considerable evidence that the mechanism of neuralization by these inducing factors is under inhibitory control and involves derepression. This review focuses on factors involved in the specification of neural fate within the frame of the default model of neural induction.

Animals↗
PubMed1990

A comparison of two temporary restorations: light-cured resin versus a self-polymerizing temporary restoration.

Temporary restorative materials are an important component of endodontic therapy. They must both adequately seal the access preparation between visits and protect the obturated canal(s) from microleakage until a permanent restoration can be placed. The efficacy of Cavit and T.E.R.M. (a new light-cured composite product) was compared with the use of a carbon black coronal microleakage protocol. The teeth examined had previously received coronal restorations. After the teeth were accessed, restored with Cavit or T.E.R.M., and exposed to the dye, they were cleared. Three-dimensional assessment then revealed that Cavit more consistently provided an effective seal. In addition, a great deal of microleakage was observed around the permanent restoration-tooth interface. This indicates that perhaps leaking permanent restorations should be removed in their entirety before initiation of endodontic treatment.

Acid Etching, Dental↗
PubMed1982

Sequences of four tRNA genes from Caenorhabditis elegans and the expression of C. elegans tRNALeu (anticodon IAG) in Xenopus oocytes.

Four tRNA genes have been identified in cloned segments of Caenorhabditis elegans DNA by tRNA hybridisation and expression after injection into Xenopus laevis oocyte nuclei. From DNA sequencing these are (with DNA anticodon sequences) tRNAAsp (GTC), tRNALeu (AAG), tRNALys (CTT) and tRNAPro (TGG). Their flanking DNA sequences are compared. Two identical tRNALys (CTT) genes from different regions of the genome have quite unrelated 5' flanking sequences. The tRNA synthesised in Xenopus oocytes after injection of the tRNALeu cloned DNA has the modified anticodon IAG. The tRNALeu gene precursor transcript from injected oocytes has short 5' and 3' additional sequences and lacks certain of those modified bases found in the processed tRNA.

Animals↗
PubMed1980

Transcription of tRNA genes in vivo: single-stranded compared to double-stranded templates.

The expression of cloned tRNA genes has been studied by injecting single-stranded and double-stranded DNA templates into Xenopus oocyte nuclei. In both forms the genes are faithfully transcribed after injection. Some single-stranded DNA is converted into double-stranded DNA in the oocyte nucleus. This conversion is necessary for the expression of the injected tRNA gene: no tRNA transcription is observed when DNA synthesis is inhibited. We conclude that single-stranded DNA does not serve as a template for faithful transcription of this gene in injected oocytes.

Coliphages↗
PubMed1978

Cloning of nematode tRNA genes and their expression in the frog oocyte.

Transfer RNA genes of the nematode Caenorhabditis elegans have been cloned in E. coli using the plasmid Col E1 as vector. The tRNAs coded by 3 hybrid plasmids were purified by hybridisation of labelled nematode tRNA with the plasmid DNAs. Each plasmid appears to code for a single distinct tRNA species. The expression of the cloned DNAs was analysed in vivo by injection into nuclei of Xenopus laevis oocytes. Evidence is presented which suggests that these nematode tRNA genes are accurately transcribed and processed in frog oocytes. Analysis of one hybrid plasmid shows that a 300 base pair DNA fragment contains both the structural gene and those regions required for its transcription in vivo. The results show that cloned eukaryotic DNAs from a heterologous source can be tested for functional gene activity in X. laevis oocytes.

Animals↗