Biomedical subjects

G R Martin

Publications and source records attributed to G R Martin.

At least 109 records · Page 6Linked to original sources

PubMed1995

The mouse Fgf8 gene encodes a family of polypeptides and is expressed in regions that direct outgrowth and patterning in the developing embryo.

Evidence is accumulating that members of the FGF gene family provide signals that act locally to regulate growth and patterning in vertebrate embryos. In this report, we provide a detailed analysis of the mouse Fgf8 gene. We have mapped the Fgf8 locus to the distal region of mouse chromosome 19, and sequenced the 5' coding region of the gene. Our data identify a new coding exon, and locate multiple splice donor and splice acceptor sites that can be used to produce at least seven transcripts encoding a family of secreted FGF8 proteins with different N termini. From these results, it appears that Fgf8 is structurally the most complex member of the FGF family described to date. In the embryo, many of the regions in which Fgf8 RNA is localized are known to direct outgrowth and patterning, including the apical ectodermal ridge of the limb bud, the primitive streak and tail bud, the surface ectoderm overlying the facial primorida and the midbrain-hindbrain junction, suggesting that FGF8 may be a component of the regulatory signals that emanate from these regions.

Amino Acid Sequence↗

PubMed1994

Noninvasive measurement of interstitial pH profiles in normal and neoplastic tissue using fluorescence ratio imaging microscopy.

The tumor interstitial pH and its modification play a significant role in cancer treatment. Current in vivo pH measurement techniques are invasive and/or provide poor spatial resolution. Therefore, there are no data on perivascular interstitial pH gradients in normal or tumor tissue. We have optically measured interstitial pH gradients with high resolution in normal and tumor (VX2 carcinoma) tissue in vivo by combining a fluorescence ratio imaging microscopy technique and the rabbit ear chamber preparation. The strengths of our approach include the ability to follow pH in the same location for several weeks and to relate these measurements to local blood flow and vascular architecture. Our results show: (a) tumor interstitial pH (6.75 units; N = 6 animals, n = 324 measurements) is significantly (P < 0.001) less than normal interstitial pH (7.23; N = 5, n = 274). This increased acidity in the tumor interstitium is in agreement with the previously reported data on this tumor; (b) with respect to pH spatial gradients in normal tissue, the interstitial pH decreased by approximately 0.32 pH units over a distance of 50 microns away from the blood vessel, while in tumor tissue, interstitial pH decreased by approximately 0.13 units over the same distance. Although the pH gradient near the vessel wall was steeper in normal tissue compared to tumor, the proton concentration gradient in normal tissue was less than that in the tumor. The approximate increase in proton concentration from 0-50 microns from the vessel was 4.5 x 10(-8)M in normal versus 5.7 x 10(-8)M in tumor tissue; (c) a simple one-dimensional diffusion-reaction model suggested that tumor tissue was producing protons at a rat 65-100% greater than normal tissue; (d) feasibility studies of temporal dynamics resulting from hyperglycemia (6 g/kg) or hypercapnia (10% CO2) led to significant (P < 0.05) interstitial pH reductions. During hyperglycemia, pH dropped by more than 0.2 pH units in about 90 min in tumor tissue but remained constant in normal tissue. Hypercapnia dramatically reduced pH by approximately 0.3 pH units in tumor tissue. Our limited studies on hyperglycemia and hypercapnia are in agreement with the previously published studies and demonstrate the capability of fluorescence ratio imaging microscopy to measure spatial as well as temporal changes in interstitial pH. Fluorescence ratio imaging microscopy should permit noninvasive evaluation of new pH-modifying agents and offer unique mechanistic information about tumor pathophysiology in tissue preparations where the surface of the tissue can be observed.

Animals↗

PubMed1994

A positive feedback loop coordinates growth and patterning in the vertebrate limb.

Limb development depends on signals from the apical ectodermal ridge and underlying mesenchyme. Fibroblast growth factor (FGF) can replace the ridge and, because Fgf4 RNA is localized to the mouse posterior ridge, we proposed that FGF4 is the endogenous ridge signal. Ridge signals control limb outgrowth and maintain the zone of polarizing activity (ZPA) at the limb posterior margin, which is important in limb pattering: a ZPA graft to limb anterior mesenchyme causes cell respecification and mirror-image duplications. Sonic hedgehog (SHH) has polarizing activity, and Shh RNA co-localizes with ZPA activity, suggesting SHH is the endogenous polarizing signal. We have investigated the molecular regulation of Fgf4 and Shh expression. We report here that Fgf4 expression in the ridge can be regulated by Shh-expressing cells. Moreover, Shh expression in mesenchyme can be activated by FGF4 in combination with retinoic acid. Once induced, Shh expression can be maintained by FGF4 alone, thus establishing a positive feedback loop between ZPA and ridge.

Amino Acid Sequence↗

PubMed1994

FGF5 as a regulator of the hair growth cycle: evidence from targeted and spontaneous mutations.

Fibroblast growth factor 5 (FGF5) is a secreted signaling protein. Mice homozygous for a predicted null allele of the Fgf5 gene, fgf5neo, produced by gene targeting in embryonic stem cells, have abnormally long hair. This phenotype appears identical to that of mice homozygous for the spontaneous mutation angora (go). The fgf5neo and go mutations fail to complement one another, and exon 1 of Fgf5 is deleted in DNA from go homozygotes, demonstrating that go is a mutant allele of Fgf5. Expression of Fgf5 is detected in hair follicles from wild-type mice and is localized to the outer root sheath during the anagen VI phase of the hair growth cycle. These findings provide evidence that FGF5 functions as an inhibitor of hair elongation, thus identifying a molecule whose normal function is apparently to regulate one step in the progression of the follicle through the hair growth cycle.

Alleles↗

PubMed1994

Altered angiogenesis underlying age-dependent changes in tumor growth.

BACKGROUND: Cancer incidence increases with age, but the growth and spread of tumors is often slow and prolonged in the elderly. Transplantable murine tumors grow and spread less readily in older mice and can be used as models to study the effect of host age. Neovascularization is crucial for the growth of solid tumors, and alterations in the host vascular response may underlie the changes in tumor growth occurring with age. PURPOSE: We have used transplantable tumor cells and tumors, and tumor extracts, to better understand differences in the biology of tumor growth and vascularization as a function of host age. METHODS: Englebreth-Holm-Swarm (EHS) carcinoma and B16-F10 melanoma cells were injected into C57BL mice of different ages. Tumor growth, histology, and cellular DNA synthesis were compared. Vascularization was determined using basic fibroblast growth factor and an in vivo angiogenesis assay. EHS tumor extracts were assayed for biologic activity in vitro using human endothelial cells and in vivo using mouse EHS-BAM carcinoma and human TSU-Pr1 prostate carcinoma cells. RESULTS: EHS tumors formed larger tumors in young than in old C57BL mice. Rapid tumor growth resumed upon transfer of tumor tissue from old animals into young animals. The rate of DNA synthesis of tumor tissue from old animals in organ culture was lower than in tissue from young animals. Histologically, tumors grown in old animals exhibited a threefold higher ratio of extracellular matrix to tumor cells than those grown in young animals. Tumors from adult animals exhibited numerous small blood vessels; those from old animals contained fewer, much larger vessels. Similar results were observed in young mice fed a reduced-calorie diet. Young animals elicited a greater and more rapid angiogenic response than old animals. Extracts of tumors grown in old animals failed to support endothelial cell differentiation in culture. Tumor cells injected together with such old extracts showed reduced tumor growth in nude mice. CONCLUSIONS: The rate of growth and morphology of the EHS tumor were altered with age, partly due to a reduced capacity to vascularize the tumors because of a lack of angiogenic factors or the presence of host inhibitors. IMPLICATIONS: Alterations in host factors detected in this tumor model may underlie a variety of age-dependent changes that could influence tumor growth and the repair and regeneration of normal tissue. Reducing the vascularization of tumors represents a potential target to reduce their growth and progression.

Aging↗

PubMed1994

Establishment of hormone-dependent and hormone-independent carcinoma cell lines with different metastatic potentials from spontaneous mammary tumors in aged Wistar rats.

Three stable carcinoma cell lines, designated RM22-F5, RM17-5R, and RM1-4, were established from spontaneously occurring mammary carcinomas in old, outbred, female Wistar rats. The RM22-F5 and RM17-5R cells were keratin-positive and formed epithelial monolayers, whereas RM1-4 cells exhibited a spindle-like morphology and intense vimentin staining. When injected into nude mice, RM22-F5, RM17-5R and RM1-4 cells formed well-differentiated, poorly differentiated and undifferentiated carcinomas, respectively. The relative growth rates of the tumor cells in vitro were RM1-4 > RM22-F5 > RM17-5R. The growth of RM22-F5, but not of RM17-5R and RM1-4 cells, was significantly stimulated by insulin, epidermal growth factor, dexamethasone, 17 beta-estradiol and progesterone in vitro. Ovariectomy reduced the growth of RM22-F5 cells in vivo and these cells (but not RM1-4 or RM17-5R) were estrogen-receptor (ER)-positive. None of the lines were positive for the progesterone receptor (PR). Spontaneous lung and lymph-node metastases were observed in nude mice injected with RM22-F5 or RM17-5R cells, respectively. In contrast, RM1-4 cells were non-metastatic but invasive. Karyotype analysis revealed that RM22-F5 cells were hyperdiploid, RM17-5R were hypotetraploid, and RM1-4 were diploid with a sizeable insertion in chromosome 1. A point mutation in codon 12 (G to A transition) and loss of the normal allele of the H-ras-1 gene was detected in the DNA from RM22-F5 cells. No p53 mutations were apparent in any of the cell lines. The results indicate that RM22-F5 cells are hormone-dependent with an ER+/PR- phenotype, while the RM17-5R and RM1-4 lines are hormone-independent and ER-/PR-. These cell lines exhibit the spectrum of biological properties and genetic alterations observed in human breast cancers and may, therefore, be novel and useful models for understanding sporadic breast cancer in post-menopausal women.

Aneuploidy↗

PubMed1994

Oncogene-induced basement membrane invasiveness in human mammary epithelial cells.

Expression of the intermediate filament protein vimentin, and loss of the cellular adhesion protein uvomorulin (E-cadherin) have been associated with increased invasiveness of established human breast cancer cell lines in vitro and in vivo. In the current study, we have further examined these relationships in oncogenically transformed human mammary epithelial cells. A normal human mammary epithelial strain, termed 184, was previously immortalized with benzo[a]pyrene, and two distinct sublines were derived (A1N4 and 184B5). These sublines were infected with retroviral vectors containing a single or two oncogenes of the nuclear, cytoplasmic, and plasma membrane-associated type (v-rasH, v-rasKi, v-mos, SV40T and c-myc). All infectants have been previously shown to exhibit some aspects of phenotypic transformation. In the current study, cellular invasiveness was determined in vitro using Matrigel, a reconstituted basement membrane extract. Lineage-specific differences were observed with respect to low constitutive invasiveness and invasive changes after infection with ras, despite similar ras-induced transformation of each line. Major effects on cellular invasiveness were observed after infection of the cells with two different oncogenes (v-rasH + SV40T and v-rasH + v-mos). In contrast, the effects of single oncogenes were only modest or negligible. All oncogenic infectants demonstrated increased attachment to laminin, but altered secretion of the 72 kDa and 92 kDa gelatinases was not associated with any aspect of malignant progression. Each of the two highly invasive double oncogene transformants were vimentin-positive and uvomorulin-negative, a phenotype indicative of the epithelial-mesenchymal transition (EMT) previously associated with invasiveness of established human breast cancer cell lines. Weakly invasive untransformed mammary epithelial cells in this study were positive for both vimentin and uvomorulin, suggesting that uvomorulin may over-ride the otherwise vimentin-associated invasiveness.

Animals↗

PubMed1994

Vascular receptors for 5-hydroxytryptamine: distribution, function and classification.

The complex actions of 5-hydroxytryptamine (5-HT) on blood vessels result from interactions with a multiplicity of specific 5-HT receptors. Dramatic advances recently have been made in defining the receptor subtypes involved in terms of their pharmacology and biochemistry, as well as their molecular biology, provoking an evolution of the criteria used for classifying and naming them. This article reviews the distribution and function of different 5-HT receptor types present on vascular smooth muscle, endothelium and perivascular neurones, and considers ways in which they can be positively defined and differentiated using traditional pharmacological approaches. The characteristics of each receptor type are also considered in terms of current biochemical and molecular perspectives on 5-HT receptor classification.

Animals↗

PubMed1994

A new nomenclature for the laminins.

The authors have adopted a new nomenclature for the laminins. They are numbered with arabic numerals in the order discovered. The previous A, B1 and B2 chains, and their isoforms, are alpha, beta and gamma, respectively, followed by an arabic numeral to identify the isoform. For example, the first laminin identified from the Engelbreth-Holm-Swarm tumor is laminin-1 with the chain composition alpha 1 beta 1 gamma 1. The genes for these chains are LAMA1, LAMB1 and LAMC1, respectively.

Animals↗

PubMed1994

Real-time, automated echocardiographic measures of ventricular area and area change: comparison with radionuclide technique.

Echocardiography now permits tracking of the blood-endocardial border and automatic measurement of ventricular area throughout the cardiac cycle. To determine the accuracy of this technique, we compared echocardiographic measurements of area with similar measurements made by radionuclide technique in 19 children, ages 4-24 years (mean 13 years). The blood-endocardial border was tracked from the apical two-chamber view and radionuclide measurements were made from the left anterior oblique view. We measured echocardiographic end-diastolic area, end-systolic area, and fractional area change from the average of five cardiac cycles. The radionuclide area measurements were made from a gated blood pool study incorporating 700-1200 cardiac cycles. Results were compared by bias analysis. The mean differences (+/- 1 S.D.) between left ventricular area measurements were: end-diastole 1.13 +/- 2.3 cm2, end-systole -0.90 +/- 1.33 cm2, and fractional area change 7.4 +/- 9.3 (%). Differences between the measurements were within the limit of agreement (mean +/- 2 S.D.) in 55 of 57 measurements. The area measurements were not free from bias; the mean differences of area measurements were significantly different from zero for end-diastolic area (P < or = 0.05), end-systolic area (P < or = 0.01), and fractional area change (P < or = 0.002). Echocardiography tended to underestimate end-diastolic area and fractional area change and it tended to overestimate end-systolic area. Real-time tracking of the blood-endocardial border is possible and allows accurate measurement of ventricular area.

Adolescent↗

PubMed1994

Visual fields and eye movements in herons (Ardeidae).

The visual fields and eye movements of three heron species (Ardeidae; Ciconiiformes): the cattle egret (Bubulcus ibis), the squacco heron (Ardeola ralloides), the western reef heron (Egretta gularis schistacea) were determined in alert, restrained birds using an ophthalmoscopic technique. All three species can gain panoramic visual coverage of the frontal field around the bill, and a bird standing with its bill horizontal can view its own feet binocularly. The region in which binocular overlap is possible is long (approximately 170 degrees) and narrow (maximum width approximately 20 degrees). Monocular field width in a horizontal plane is approximately 170 degrees. Retinal binocular overlap can be abolished by eye movements at all elevations in the frontal field. At the frontal margins of the monocular fields the retinal and optical field margins do not coincide; the retinal field margin lies between 9 degrees and 12.5 degrees inside the optical field margin. This results in a blind sector at the margin of each eye's optical field. Consequently the visually functional retinal binocular field widths are significantly narrower than the optical binocular fields. When retinal binocularity is abolished by eye movements, optical binocular fields are still retained. Thus, estimates of binocular overlap based only upon the appearance of the pupils will be erroneous. The comprehensive nature of vision beneath the bill is probably closely associated with the herons' visually guided, stealthy, foraging techniques, which result in the single-strike capture of mobile, highly evasive prey.

Animals↗

PubMed1994

International Union of Pharmacology classification of receptors for 5-hydroxytryptamine (Serotonin).

It is evident that in the last decade or so, a vast amount of new information has become available concerning the various 5-HT receptor types and their characteristics. This derives from two main research approaches, operational pharmacology, using selective ligands (both agonists and antagonists), and, more recently, molecular biology. Although the scientific community continues to deliberate about the hierarchy of criteria for neurotransmitter receptor characterisation, there seems good agreement between the two approaches regarding 5-HT receptor classification. In addition, the information regarding transduction mechanisms and second messengers is also entirely consistent. Thus, on the basis of these essential criteria for receptor characterisation and classification, there are at least three main groups or classes of 5-HT receptor: 5-HT1, 5-HT2, and 5-HT3. Each group is not only operationally but also structurally distinct, with each receptor group having its own distinct transducing system. The more recently identified 5-HT4 receptor almost undoubtedly represents a fourth 5-HT receptor class on the basis of operational and transductional data, but this will only be definitively shown when the cDNA for the receptor has been cloned and the amino acid sequence of the protein is known. Although those 5-HT receptors that have been fully characterised and classified to date (and, hence, named with confidence) would seem to mediate the majority of the actions of 5-HT throughout the mammalian body, not all receptors for 5-HT are fully encompassed within our scheme of classification. These apparent anomalies must be recognised and need further study. They may or may not represent new groups of 5-HT receptor or subtypes of already known groups of 5-HT receptor. Even though the cDNAs for the 5-ht1E, 5-ht1F, 5-ht5, 5-ht6, and 5-ht7 receptors have been cloned and their amino acid sequence defined, more data are necessary concerning their operational and transductional characteristics before one can be confident of the suitability of their appellations. Therefore, it is important to rationalise in concert all of the available data from studies involving both operational approaches of the classical pharmacological type and those from molecular and cellular biology.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1994

Mechanisms of change in cardiac performance in infants undergoing extracorporeal membrane oxygenation.

OBJECTIVE: To determine whether changes in cardiac performance observed in infants early during extracorporeal membrane oxygenation are due to the underlying disease process, the partial bypass procedure, changes in cardiac loading conditions, or due to a direct myocardial effect of hypoxia-reoxygenation. DESIGN: Consecutive case series. PATIENTS: Infants with meconium aspiration syndrome were studied at the end of their extracorporeal membrane oxygenation course (veno-arterial, n = 12; veno-venous, n = 8), after lung compliance and pulmonary arterial pressure returned toward normal and they were ready to have extracorporeal membrane oxygenation discontinued. INTERVENTIONS: Heart rate, mean arterial blood pressure, and load-dependent indices, and a load-independent index of cardiac performance were measured at increasing bypass flow rates (25, 50, 75, 100, 125 mL/kg/min). MEASUREMENTS AND MAIN RESULTS: Heart rate, mean arterial blood pressure, and load-dependent indices of cardiac performance (left ventricular shortening fraction and stroke volume) were normal at 25 mL/kg/min bypass flow rate and did not change significantly with increasing bypass flow rates. The load-independent index of performance was within the normal range for infants and did not change significantly with increasing bypass flow rates. CONCLUSIONS: The previously described decreases in cardiac performance during extracorporeal membrane oxygenation are not due to the underlying disease process or the bypass procedure but are due to changes in loading conditions during partial bypass.

Echocardiography↗

PubMed1993

FGF-4 replaces the apical ectodermal ridge and directs outgrowth and patterning of the limb.

The apical ectodermal ridge plays a key role in limb development. We show that recombinant FGF-4 can substitute for the ridge to provide all the signals necessary for virtually complete outgrowth and patterning of the chick limb. FGF-4 stimulates proliferation of cells in the distal mesenchyme and maintains a signal from the posterior to the distal mesenchyme that appears to be required for elaboration of skeletal elements in the normal proximodistal sequence. Moreover, retinoic acid, which is capable of providing polarizing activity, can supply this signal. This suggests that polarizing activity plays a role in patterning along the proximodistal axis, in addition to its well-established role in anteroposterior patterning. Taken together, the data suggest a simple mechanism whereby FGF-4 links growth and pattern formation during limb development.

Animals↗

PubMed1993

FGF-4 and BMP-2 have opposite effects on limb growth.

Limb development is dependent on epithelial-mesenchymal interactions. The apical ectodermal ridge (AER), a specialized epithelium at the limb tip, stimulates proliferation of underlying mesenchyme, causing directed limb outgrowth (for review see ref. 2). Several genes are expressed in the mouse AER, including Fgf-4 (fibroblast growth factor-4) and Bmp-2 (bone morphogenetic protein-2), both of which encode secreted signalling molecules. Using a culture system developed to explore the function of molecules produced by the AER, we have shown that FGF-4 protein stimulates proliferation of mesenchyme in the early mouse limb-bud. This suggests that FGF-4 serves that major function of the AER. In contrast, BMP-2 inhibits limb growth, suggesting that as a result the AER may serve a hitherto unrecognized inhibitory function. Furthermore, the extent of limb outgrowth can be modulated by mixing the two signalling molecules, suggesting that limb growth is regulated by a combination of stimulatory and inhibitory signals from the AER.

Animals↗

PubMed1993

Embryonic expression of Fgf-6 is restricted to the skeletal muscle lineage.

As part of an ongoing examination of the functions of the fibroblast growth factor (FGF) gene family in mammalian development, we have carried out an RNA in situ hybridization analysis of the Fgf-6 gene in the mouse embryo. In contrast to what has been found for three other members of the FGF gene family, no Fgf-6 RNA was detected in mouse embryos at E6.5 through E8.5. Fgf-6 RNA was first detected in embryos at E9.5 and was localized exclusively in the myotomal compartment of the somite. Similar results were obtained with embryos at E10.5 and E11.5. At E12.5, expression was still detected in the myotome, and also in the region containing the developing muscles of the body wall. By E14.5, Fgf-6 RNA was found in the majority of skeletal muscles in the fetus. These results are discussed in comparison with what is known about the expression patterns of the genes encoding other FGF family members, as well as their high-affinity receptors.

Animals↗

PubMed1993

Fluorescence ratio imaging measurement of pH gradients: calibration and application in normal and tumor tissues.

The fluorescence ratio imaging technique is currently applied in vitro and in vivo to measure intracellular as well as extracellular pH. To date, however, no effort has been made to assess the technique's ability to detect spatial pH gradients in vitro or in vivo, where pH gradients are known to exist, in a controlled environment using an independent pH measurement system. We present here both in vitro calibration and in vivo application of fluorescence ratio imaging to measure pH gradients in a biologically useful pH range (6.2-7.8). Isoelectric focusing in short polyacrylamide gels was used to establish spatial pH gradients ranging from approximately 0.2 to 0.5 pH units/mm. The pH gradients were measured independently with fluorescence ratio imaging microscopy (FRIM) and a surface electrode. The average difference between measurements using the two techniques was 0.043 pH units for 10-mm polyacrylamide gels (100 measurements in 12 gels) and 0.046 pH units for 20-mm gels (114 measurements in 15 gels). These gel studies have demonstrated the use of isoelectric focusing to calibrate FRIM for measuring spatial pH gradients characteristic of those found in tumors in vivo. The feasibility of FRIM was tested in vivo by measuring pH in a solid tumor (VX2 carcinoma) and surrounding normal granulation tissue grown in the rabbit ear chamber. The average (+/- SD) pH of normal and neoplastic regions of the composite tissue was 7.18 +/- 0.11 (n = 158) and 6.75 +/- 0.10 (n = 191), respectively. The pH varied by an average of approximately 0.6 pH units over the 5-mm diameter of the chamber and showed a sharp difference at the interface of the two tissue types. These pH values are consistent with the current pH data on normal and neoplastic tissues. Thus FRIM should permit noninvasive in vivo evaluation of new pH-modifying agents and, in combination with other optical techniques, should offer novel mechanistic information about tumor pathophysiology.

Animals↗

PubMed1993

Cyclic AMP decreases chemotaxis, invasiveness and lung colonization of H-ras transformed mouse fibroblasts.

We transfected mouse 10T1/2 fibroblasts with the H-ras oncogene and isolated lines expressing H-ras. One of the lines exhibited a highly malignant phenotype with the ability to produce large tumors and to colonize the lung after tail vein injection. In addition, the cells of this line showed increased collagenase IV production, directed migration and invasiveness, properties associated with the ability of tumor cells to metastasize. Since cyclic adenosine 3',5'-monophosphate (cAMP) is known to down-regulate ras expression, we exposed the malignant cells (Cl-1) to either N6, 2',0-dibutyryl cAMP (DB-cAMP) or 8-bromo cAMP (8-Br-cAMP), either with or without a phosphodiesterase inhibitor. We found that these treatments reduced the expression of ras, chemotaxis, invasiveness, and lung colonization of the ras-transformed cells. We therefore postulate that the malignancy of some cells may be regulated by alterations in the intracellular cAMP levels by suppressing ras expression and/or by reducing other activities required for the dissemination of tumor cells.

1-Methyl-3-isobutylxanthine↗