Biomedical subjects

D L Clarke

Publications and source records attributed to D L Clarke.

33 records · Page 2Linked to original sources

PubMed2000

Generalized potential of adult neural stem cells.

The differentiation potential of stem cells in tissues of the adult has been thought to be limited to cell lineages present in the organ from which they were derived, but there is evidence that some stem cells may have a broader differentiation repertoire. We show here that neural stem cells from the adult mouse brain can contribute to the formation of chimeric chick and mouse embryos and give rise to cells of all germ layers. This demonstrates that an adult neural stem cell has a very broad developmental capacity and may potentially be used to generate a variety of cell types for transplantation in different diseases.

Animals↗

PubMed2000

Mapping of the Cryptococcus neoformans MATalpha locus: presence of mating type-specific mitogen-activated protein kinase cascade homologs.

In this study we investigated the relationship between the MATalpha locus of Cryptococcus neoformans and several MATalpha-specific mitogen-activated protein (MAP) kinase signal transduction cascade genes, including STE12alpha, STE11alpha, and STE20alpha. To resolve the location of the genes, we screened a cosmid library of the MATalpha strain B-4500 (JEC21), which was chosen for the C. neoformans genome project. We isolated several overlapping cosmids spanning a region of about 71 kb covering the entire MATalpha locus. It was found that STE12alpha, STE11alpha, and STE20alpha are imbedded within the locus rather than closely linked to the locus. Furthermore, three copies of MFalpha, the mating type alpha-pheromone gene, a MATalpha-specific myosin gene, and a pheromone receptor (CPRalpha) were identified within the locus. We created a physical map, based on the restriction enzyme BamHI, and identified both borders of the MATalpha locus. The MATalpha locus of C. neoformans is approximately 50 kb in size and is one of the largest mating type loci reported among fungi with a one-locus, two-allele mating system.

Chemoreceptor Cells↗

PubMed1999

Identification of a neural stem cell in the adult mammalian central nervous system.

New neurons are continuously added in specific regions of the adult mammalian central nervous system. These neurons are derived from multipotent stem cells whose identity has been enigmatic. In this work, we present evidence that ependymal cells are neural stem cells. Ependymal cells give rise to a rapidly proliferating cell type that generates neurons that migrate to the olfactory bulb. In response to spinal cord injury, ependymal cell proliferation increases dramatically to generate migratory cells that differentiate to astrocytes and participate in scar formation. These data demonstrate that ependymal cells are neural stem cells and identify a novel process in the response to central nervous system injury.

Animals↗

PubMed1999

Universal primary colonic repair in the firearm era.

All patients with colonic trauma treated at King Edward VIII Hospital, Durban, from August 1993 to May 1994 underwent primary repair of the colonic wound. They were evaluated prospectively to assess the mode of injury and outcome variables. Colonic injuries were sustained by 102 patients. These were inflicted by gunshots (62), stabs (22), shotguns (14), and blunt trauma (4). The transverse colon was injured most frequently (53). All shotgun injuries were multiple. Average time from admission to theatre was similar for shocked and non-shocked patients. Eighty-seven patients had simple closure (18 deaths) and 15 required resection and anastomosis (eight deaths). Ten patients died in the first 48 h, and 16 died subsequently owing to multiple-organ systems dysfunction. The mortality rates were stabs 9% (2), gunshots 27% (17), shotguns 50% (7), and 0% for blunt trauma. Septic morbidity was seen in 16 but was not related to breakdown of the colonic repair. Implementation of strategies to reduce preoperative time delays and use damage control principles for the management of massive trauma should be evaluated as methods of reducing mortality.

Adolescent↗

PubMed1999

Inferior vena caval injury in the firearm era.

BACKGROUND: This study compared the outcome of intra-abdominal caval injuries in the current era of firearm injuries with the outcome during the previous era of stab wounds. METHODS: Patients with intra-abdominal vena caval injuries treated at King Edward VIII Hospital, Durban, from December 1990 to December 1995 were reviewed. This group was compared with a similar cohort reviewed a decade earlier. RESULTS: The historical group consisted of 28 patients and the current group of 26 patients. Modes of injury in the historical group were: stabs (15, 53%), firearm injuries (7, 33%), blunt trauma (4, 14%) and iatrogenic injuries (2, 7%). Modes of injury in the current group were: stabs (5, 19%), firearm injuries (17, 65%) and blunt trauma (4, 16%). Mortality rose from 35.7% in the historical group to 88% in the current series. This mortality figure included 5 patients who died later from complications of the associated injuries. CONCLUSIONS: Firearm injuries are more destructive than stab wounds. The increase in firearm injuries partly explains this higher mortality. However, the failure to apply current concepts of abbreviated laparotomy and damage control combined with excessive delays in transferring patients to theatre have contributed to this high mortality.

Adolescent↗

PubMed1997

Cloning and characterisation of the adenosyl phosphosulphate kinase gene from Aspergillus nidulans.

The sD gene of Aspergillus nidulans has been cloned by heterologous screening of rationally selected cosmids. Co-transformation of the sD50 mutant JMP1 confirmed the presence of a functional gene. Sequence analysis determined this gene to be 680 bp in length, containing a 59-bp intron and encoding a protein of 206 amino acids. A protein-sequence comparison revealed a similarity to the C-terminal region of ATP sulphurylase, the sC gene product. Further sequence comparison revealed differences in a consensus sequence ATP-binding motif, indicating non-functionality of the APS kinase-like domain of ATP sulphurylase, and confirms sD as the gene encoding APS kinase in A. nidulans.

Amino Acid Sequence↗

PubMed1997

The different forms of the prolactin receptor in the rat corpus luteum: developmental expression and hormonal regulation in pregnancy.

The corpora lutea of pregnancy in the rat are highly dependent on the action of PRL and PRL-like hormones to hypertrophy and to produce progesterone needed for the maintenance of gestation. Two forms of the PRL receptor (PRL-R), designated as long (PRL-RL) and short (PRL-RS), have been described in rat tissues. To determine whether both forms are present in the corpus luteum during pregnancy and to examine the developmental and hormonal regulation of their expression, total RNA isolated from corpora lutea at different stages of pregnancy and from highly luteinized granulosa cells subjected to different hormonal treatments were analyzed by semiquantitative RT-PCR. Immunoblotting of luteal proteins from early and late pregnancy was also performed to determine if the pattern of PRL-R proteins follows that of PRL-R messenger RNA (mRNA) expression. In addition, the correlation between the well characterized PRL-regulated gene, 20alpha-hydroxysteroid dehydrogenase (20alpha-HSD), and PRL-R gene expression was investigated during the time of luteolysis. Both PRL-RL and PRL-RS mRNA and protein were expressed in corpora lutea of pregnancy, with the long form being the most dominant at all stages. Whereas no changes in mRNA level of either PRL-RL or PRL-RS were found until day 20 of gestation, a profound decline in PRL-R mRNA and protein for both receptor types occurred at the end of pregnancy. This drop in PRL-R expression was accompanied by a sharp and abrupt expression of 20alpha-HSD mRNA. Studies performed in vivo and in luteinized cells in culture indicate that PRL can up-regulate the expression of the PRL-RL mRNA, an effect prevented by the tyrosine kinase inhibitor, genistein. PRL-RL mRNA was also selectively increased by cAMP. In summary, the results of this investigation have established that: 1) the corpus luteum of pregnancy expresses both the short and long forms of the PRL-R with the long form being more abundant; 2) the mRNA for both forms of the PRL-R remains at constant levels throughout pregnancy but drops before parturition; 3) the decline in PRL-R mRNA at the end of pregnancy is accompanied by a dramatic rise in 20alpha-HSD; 4) PRL is able to increase the expression of PRL-R mRNA; and that 5) both A kinase and tyrosine kinase mediated pathways appear to participate in the up-regulatory mechanism involved in PRL-R mRNA expression.

20-Hydroxysteroid Dehydrogenases↗

PubMed1996

The decidual prolactin receptor and its regulation by decidua-derived factors.

Decidualization of the endometrial stroma in the rat gives rise to two different cell populations, located either mesometrially or antimesometrially in the uterus. We have previously shown that the rat decidua is the site of production and action of a PRL-like hormone. In this investigation we examined, using reverse transcription-PCR, whether and which type of PRL receptor (PRL-R) messenger RNA (mRNA) is expressed in the decidua, whether the receptor is confined only to one cell population, and whether the PRL-R expression is regulated by decidua-derived factors. The results indicate that the uterus of pseudopregnant rats does not express the PRL-R and that decidualization does not trigger a rapid appearance of PRL-R mRNA. It is only 3 days after the induction of decidualization that the long form of the PRL-R was first expressed. Thereafter, mRNAs for both the short (PRL-RS) and the long (PRL-RL) form became detectable in both antimesometrial and mesometrial decidua, although PRL-RL mRNA was much more abundant than PRL-RS. As development proceeded, PRL-R mRNA decreased and disappeared specifically from the antimesometrial decidua, whereas the mesometrial decidua continued to express this receptor mRNA. Concomitant with down-regulation of the PRL-R in the antimesometrial tissue was a rather abrupt expression of activin A. In contrast, the mesometrial tissue that maintained high levels of PRL-R mRNA expressed little activin A, but produced an activin-binding protein, alpha(2)-macroglobulin (alpha(2)MG). To determine whether activin A and alpha(2)MG regulate PRL-R expression, antimesometrial and mesometrial cells were separated by elutriation and maintained in culture in the presence or absence of activin A, alpha(2)MG, or follistatin. Just after cell separation, both cell populations expressed PRL-R, but not activin A. Within 6 h, activin A mRNA and protein became highly expressed in the mesometrial cells, whereas PRL-RL mRNA became undetectable. In contrast, activin A mRNA was at very low levels in the antimesometrial cells, and no activin A protein could be detected in the medium for at least 12 h. In these cells PRL-RL mRNA remained elevated. Addition of activin A to antimesometrial cells caused a marked down-regulation of PRL-RL mRNA expression, whereas addition of alpha(2)MG and follistatin to mesometrial cells prevented the disappearance of PRL-R. In summary, the results of this investigation 1) indicate that decidualization of the endometrial stroma induces the appearance of both forms of the PRL-R mRNAs; 2) show differential expression of the PRL-R mRNA in the two-cell population forming the decidua; 3) establish that this differential expression is due to two key decidual molecules, activin A and alpha(2) macroglobulin; and 4) demonstrate that activin A can cause the decidual cells to lose the PRL-R and that the disappearance of the decidual PRL-R can be prevented by addition to the culture of two activin binding proteins, follistatin and alpha(2) MG.

Activins↗

PubMed1993

Changes in prolactin receptor expression during pregnancy in the mouse ovary.

We have isolated the cDNA encoding the cytoplasmic domain of a long form of the mouse PRL receptor (PRL-R). The mRNA for this long form PRL-R and the three mRNAs encoding short mouse PRL-R that have been previously characterized are all expressed in both the liver and ovary. The relative amounts of these receptor forms differ between tissues, however. In addition, the structure of one of the short receptor forms may not be identical in the liver and ovary. Within the ovary, the abundance and sites of synthesis of the four PRL-R mRNAs vary during pregnancy. Expression of the two most abundant PRL-R mRNAs increases significantly at midgestation. Expression of PRL-R mRNA is detected in the corpus luteum throughout pregnancy, while increased receptor mRNA levels are evident in the granulosa cells of a subset of Graafian follicles toward the end of pregnancy and during lactation. Some differences are also observed in the expression patterns of the individual receptor forms. Most notably, one of the short form PRL-R mRNAs is uniquely detected in atretic follicles in early to midgestation.

Amino Acid Sequence↗

PubMed1993

Prolactin receptor messenger ribonucleic acid expression in the ovary during the rat estrous cycle.

We have investigated the relative amounts and sites of synthesis during the rat estrous cycle of the two ovarian mRNAs encoding the long and short PRL receptors (PRL-R). Quantitative analysis has revealed that the mRNA encoding the short PRL-R is consistently present throughout the cycle in lower quantities than the long receptor mRNA. Both receptor mRNAs are at maximal levels during proestrus, decline to their lowest level of expression during estrus, then gradually rise in metestrus and diestrus. By in situ hybridization, both receptor mRNAs are present during early proestrus in corpora lutea, in the granulosa cell layers of large Graafian follicles, and in the interstitial cells closely associated with these follicles. The short PRL-R mRNA was detected at significant levels in the granulosa-derived cumulus oophorus and in the thecal cell region at this time, whereas the long PRL-R mRNA was only weakly expressed in these cell types. In contrast, the long PRL-R mRNA was present at higher levels, compared to the short receptor mRNA, in the granulosa cells of preantral follicles in the interior of the ovary. On late proestrus, the long PRL-R mRNA was found predominantly in the mural granulosa cells of large Graafian follicles and in corpora lutea, but by estrous morning this mRNA appeared to be mostly restricted to the corpora lutea. This distribution was maintained through estrous evening and metestrous morning. On diestrus, both mRNAs were present in some corpora lutea and in the granulosa cell layer in a subset of the larger Graafian follicles, but were detected at even higher levels in the interstitial cells surrounding these follicles; again, the long receptor mRNA appeared to be only weakly expressed in the thecal cell region of these follicles. These results indicate that the levels and locations of PRL-R mRNA expression in the ovary, and therefore, the potential responsiveness of the ovary to PRL, change throughout the reproductive cycle. Furthermore, the presence of both receptor mRNAs in several different ovarian cell types suggests that both of these receptor forms play important roles in PRL physiology in the ovary.

Animals↗

PubMed1992

Simulation of coherent energy transfer in an alpha-helical peptide by Fermi resonance.

A mechanism by which NH stretching quanta are coherently transported along a chain of hydrogen bonded peptide groups is demonstrated by classical simulation of a section of the alpha-helical peptide poly(L-alanine). Vibrational motion takes place on a complex energy surface constructed from earlier ab initio and empirical surfaces. A speculative hypothesis of the biological role of this mechanism is presented, and the critical parameters governing the dynamics are identified and discussed.

Acetamides↗

PubMed1989

Rocking promotes differentiated properties in LLC-PK cells by improved oxygenation.

Previous studies from our laboratory indicated that in contrast to cells cultured under still conditions, LLC-PK cells cultured under conditions of continuous rocking exhibit pH-modulated ammonia production and also manifest lower levels of lactate dehydrogenase activity. In the present studies, we assessed whether other metabolic features and parameters of differentiation are modified by rocking. Rocked, as contrasted with still, cultures exhibited decreased medium lactate production and increased cellular ATP content consistent with heightened oxidative metabolism. Still cultures did not exhibit either dome formation or sodium-dependent alpha-methylglucoside uptake until the cultures reached full confluency. By contrast, rocked cultures underwent dome formation as well as enhanced alpha-methylglucoside uptake during the growth phase, and these parameters were quantitatively greater than in still culture even after full confluency was achieved. Thus rocking promotes several functions, which can reflect differentiation in LLC-PK cells. To determine whether provision of adequate oxygen accounts for the enhancement of cellular metabolism and differentiated functions by rocking, still cultures grown in a high oxygen concentration of 36% were compared with standard cultures grown in 18% oxygen. The high oxygen environment resulted in the development of pH-modulated ammonia production, a decrease in lactate dehydrogenase activity, lower medium lactate formation, increased ATP levels, more copious dome formation, and increased alpha-methylglucoside uptake. Thus rocking promotes cellular metabolism and differentiated functions by the provision of adequate oxygenation.

Adenosine Triphosphate↗

PubMedDate not supplied

Merging PICU and MICU: expanding nurse competencies.

Unit mergers offer an opportunity for nurses to acquire additional skills. A model for unit mergers is presented. The authors describe how didactic and clinical competencies serve as a foundation upon which the nurse develops proficiency and expertise in a new subspecialty.

Adult↗

PubMedDate not supplied

Merging a PICU and MICU: a debate.

One of the possible combinations when merging specialty units is combining a pediatric intensive care unit with an adult intensive care unit. The response related to the merging of these specialty units solicits very intense, diverse opinions. The authors address this controversial issue in a debate forum to present both sides of the issue.

Adult↗

PubMedDate not supplied

Attenuated gastric mucosal blood flow predicts non-healing of benign gastric ulcers.

BACKGROUND: A subset of benign gastric ulcers do not respond to therapy and may require surgery. A predictor of non-healing may allow modification of therapy. Gastric mucosal blood flow plays an important role in gastric ulcer pathogenesis and healing. AIMS: Mucosal blood flow was measured with Laser Doppler flowmetry at initiation of and during therapy to assess the variability of mucosal blood flow in healing and non-healing ulcers as a possible predictor of healing. METHODS AND SUBJECTS: Mucosal blood flow was measured at the mid-antrum in 105 normal human stomachs and on the circumference of 26 benign gastric ulcers. The gastric ulcers were followed up with repeat endoscopy and repeat measurements were made. RESULTS: The ulcers that healed had significantly higher mucosal blood flow than normal stomachs at both initial and follow-up measurement (59.8 +/- 26.1 vs. 75.7 +/- 17.5 and 69.8 +/- 13.7). The refractory ulcers persistently had significantly lower mucosal blood flow than normal stomachs and healing ulcers (59.8 +/- 26.1 vs. 45.2 +/- 21.9 and 39.2 +/- 6.7). CONCLUSIONS: Gastric mucosal blood flow seems to increase in response to mucosal injury and healing. Attenuation of this response is associated with delayed healing. Attenuated peri-ulcer mucosal blood flow may predict non-healing of a benign gastric ulcer.

Adult↗