Incomplete Data Sets in Community Ecology and Biogeography: A Cautionary Tale

Many basic and applied studies in ecology, biogeography, and conservation biology rely on data on the distribution of species and the composition of communities that are compiled from the literature or from unpublished sources. Most of these data sets are incomplete, and some contain serious biases. We examine two such data sets. New records of fishes in Australian desert springs, which corrected sampling biases in the original study, revealed different patterns of species distribution and community structure. New records of mammals on Great Basin mountaintops did not materially alter the results and interpretations of earlier studies. In order to avoid serious errors of fact, interpretation, and application, there is no substitute for first-hand field experience with the organisms and habitats.

A requirement for Ras protein function in thrombin-stimulated mitogenesis in astrocytoma cells

Thrombin stimulation of 1321N1 astrocytoma cells results in polyphosphoinositide hydrolysis, Ca2+ mobilization, AP-1-mediated transcriptional activation, and DNA replication. Thrombin stimulation also activates Ras as assessed by an increase in the proportion of Ras in a GTP bound state. We examined the functional requirement for endogenous Ras protein in mediating thrombin-induced responses. Microinjection of a dominant interfering mutant of H-Ras into 1321N1 cells inhibited DNA synthesis in response to thrombin as did microinjection of an inhibitory antibody to Ras. Stimulation of AP-1-mediated transcriptional activity was also reduced by the expression of interfering Ras mutants. However, neither the stimulation of polyphosphoinositide hydrolysis nor the mobilization of intracellular Ca2+ was dependent on endogenous Ras function. These observations indicate that thrombin stimulation of mitogenesis requires Ras protein function. Our data suggest that the G-protein-coupled thrombin receptor stimulates pathways, which in part are convergent with those stimulated by tyrosine kinase growth factor receptors.

Rotator cuff: evaluation with fat-suppressed MR arthrography

Thirty-seven shoulders with rotator cuff diagnoses proved at arthrography, arthroscopy, or open surgery were examined prospectively with magnetic resonance (MR) arthrography. T1-weighted MR images were obtained with and without fat suppression after intraarticular injection of gadopentetate dimeglumine. Without fat suppression, overall accuracy was 84%. False-positive full-thickness tears were diagnosed in three patients who were proved to have partial tears. False-negative normal tendons were diagnosed in two patients who had partial tears. The corresponding sensitivity and specificity were 90% and 75%, respectively. With the aid of fat-suppressed imaging, full-thickness and partial cuff tears were identified with 100% sensitivity and specificity. Fat-suppressed images also showed intratendinous contrast material imbibition in three torn cuffs with frayed, friable tendon margins. Fat suppression in MR arthrography is valuable in the differentiation of partial from full-thickness cuff tears and in the detection of small partial tears of the inferior tendon surface.

The alpha 1A-adrenergic receptor subtype mediates biochemical, molecular, and morphologic features of cultured myocardial cell hypertrophy

alpha 1-Adrenergic agonists induce a hypertrophic phenotype in cultured neonatal rat ventricular myocytes. Quantifiable markers of this phenotype include stimulation of phosphoinositide hydrolysis, transcriptional induction of atrial natriuretic factor (ANF) gene expression, and an increase in myocardial cell size. The aim of the present work was to determine which alpha 1-adrenergic receptor subtype mediates the acquisition of these parameters of myocardial cell hypertrophy. Phosphoinositide hydrolysis is inhibited by low concentrations of 5-methylurapidil (log Ki = -8.7) and (+)-niguldipine (log Ki = -10.6). The alpha-adrenergic receptor-induced increase in transcriptional activation of an ANF luciferase reporter gene is inhibited over the same range of concentrations of 5-methylurapidil (log Ki = -8.2) and (+)-niguldipine (log Ki = -11.2) that inhibit phosphoinositide hydrolysis. In addition, the increase in cell size that accompanies alpha-adrenergic receptor stimulation of cultured ventricular myocytes is blocked by similar concentrations of 5-methylurapidil (log Ki = -8.0) and (+)-niguldipine (log Ki = -10.6). In contrast, treatment with the alpha 1B selective antagonist chlorethylclonidine at a concentration of 10 microM had no effect on the adrenergically mediated induction of ANF luciferase reporter gene expression or the adrenergically induced increase in myocardial cell size. These findings demonstrate that pharmacologically identifiable alpha 1A-adrenergic receptors mediate not only the early effects of alpha 1-adrenergic stimulation such as phosphoinositide hydrolysis, but that they activate the signaling pathways that control transcriptional induction of the ANF luciferase reporter gene and an increase in myocardial cell size. Studies using alpha 1-adrenergic receptor cDNAs to delineate and alter the direct interaction of this receptor subtype with proximal signaling molecules, e.g. GTP binding proteins, should provide a powerful means of assessing their role in the induction of the molecular and morphologic parameters of myocardial cell hypertrophy.

Three-dimensional structure of the human class II histocompatibility antigen HLA-DR1

The three-dimensional structure of the class II histocompatibility glycoprotein HLA-DR1 from human B-cell membranes has been determined by X-ray crystallography and is similar to that of class I HLA. Peptides are bound in an extended conformation that projects from both ends of an 'open-ended' antigen-binding groove. A prominent non-polar pocket into which an 'anchoring' peptide side chain fits is near one end of the binding groove. A dimer of the class II alpha beta heterodimers is seen in the crystal forms of HLA-DR1, suggesting class II HLA dimerization as a mechanism for initiating the cytoplasmic signalling events in T-cell activation.

Renal replacement therapy in multiple myeloma and systemic amyloidosis

Renal failure frequently complicates both multiple myeloma and systemic amyloidosis. Renal replacement therapy (RRT) may be poorly tolerated and its role in such patients is not clearly defined. Of fifty patients (26 males and 24 females) referred to a single centre because of renal failure associated with multiple myeloma or systemic amyloidosis 37 progressed to end-stage renal failure and 30 of these patients received RRT. Nine patients have been treated by CAPD, 13 by haemodialysis, and 8 patients have required both forms of dialysis. Overall one year and two year survival rates were 66% and 57% respectively. The median duration on RRT was 7.5 months (range 1-96 months) with a 51% one year, and a 46% two year survival rate. Of 7 patients with amyloidosis who underwent renal transplantation, 3 died within 6 months of transplantation. Undiagnosed cardiac involvement contributed to this early mortality. We conclude that renal replacement therapy is appropriate for some patients with multiple myeloma and systemic amyloidosis who develop endstage renal failure. Careful assessment and selection of patients is necessary prior to renal transplantation.

Phenylephrine and endothelin differentially stimulate cardiac PI hydrolysis and ANF expression

In ventricular myocytes, phenylephrine (PE) and endothelin (ET) stimulate phosphoinositide (PI) hydrolysis, cell growth, and expression of several genes [e.g., atrial natriuretic factor (ANF)] often associated with cardiac hypertrophy. In this study the production of inositol monophosphate (InsP) and diglyceride (DG), both products of PI hydrolysis, and ANF were monitored during long-term exposure (up to 72 h) to PE or ET. For PE, InsP production increased and continued unabated throughout the time course; DG levels also increased and remained elevated, and similar rates of ANF production were observed from 24 to 72 h. For ET, the initial InsP and DG responses equaled those to PE, but diminished by 24 h. ET-stimulated ANF production equaled the PE response at 24 h but subsided by 72 h. Adding PE to cells previously desensitized to ET elicited maximal InsP formation, indicating the desensitization was ET specific. These data emphasize that while phenylephrine and endothelin have similar initial effects on cardiac second messenger production and ANF expression, hormonally specific patterns develop over extended periods of exposure.

Binding of influenza virus hemagglutinin to analogs of its cell-surface receptor, sialic acid: analysis by proton nuclear magnetic resonance spectroscopy and X-ray crystallography

The interaction between influenza virus hemagglutinin and its cell-surface receptor, 5-N-acetylneuraminic acid (sialic acid), was probed by the synthesis of 12 sialic acid analogs, including derivatives at the 2-carboxylate, 5-acetamido, 4-, 7-, and 9-hydroxyl, and glycosidic positions. The equilibrium dissociation constants of these analogs were determined by nuclear magnetic resonance spectroscopy. Ligand modifications that reduced or abolished binding included the replacement of the 2-carboxylate with a carboxamide, the substitution of azido or N-benzyloxycarbonyl groups for the 5-acetamido group, and the replacement of the 9-hydroxyl with amino or O-acetyl moieties. Modifications having little effect on binding included the introduction of longer chains at the 4-hydroxyl position, the replacement of the acetamido methyl group with an ethyl group, and the removal of the 7-hydroxyl group. X-ray diffraction studies yielded 3 A resolution crystal structures of hemagglutinin in complex with four of the synthetic analogs [alpha-2-O-methyl-, 4-O-acetyl-alpha-2-O-methyl-, 9-amino-9-deoxy-alpha-2-O-methyl-, and alpha-2-O-(4'-benzylamidocarboxybutyl)-N-acetylneuraminic acid] and with the naturally occurring cell-surface saccharide (alpha 2-3)sialyllactose. The X-ray studies unambiguously establish the position and orientation of bound sialic acid, indicate the position of the lactose group of (alpha 2-3)sialyllactose, and suggest the location of an alpha-glycosidic chain (4'-benzylamidocarboxybutyl) that increases the binding affinity of sialic acid by a factor of about 3. Although the protein complexed with alpha-2-O-methylsialic acid contains the mutation Gly-135-->Arg near the ligand binding site, the mutation apparently does not affect the ligand's position. The X-ray studies allow us to interpret the binding affinities in terms of the crystallographic structure. The results suggest further experiments which could lead to the design of tight binding inhibitors of possible therapeutic value.

Biphasic increase in c-jun mRNA is required for induction of AP-1-mediated gene transcription: differential effects of muscarinic and thrombin receptor activation

Activation of either muscarinic cholinergic or thrombin receptors increases phosphoinositide turnover, Ca2+ mobilization, and redistribution of protein kinase C and induces rapid transient increases in c-fos mRNA and c-jun mRNA in 1321N1 cells. To determine whether the increases in c-fos and c-jun mRNA induced by carbachol and thrombin are sufficient to stimulate AP-1-mediated transactivation, 1321N1 cells were transfected with a reporter carrying two copies of the tetradecanoyl phorbol acetate response element and the firefly luciferase gene. Thrombin was significantly more effective than carbachol at stimulating AP-1-mediated transactivation. To identify the factors underlying the difference in AP-1 activity induced by carbachol and thrombin, members of the fos and jun families which encode components of AP-1 were examined. Carbachol and thrombin have similar effects on expression of c-fos, fosB, fra-2, junB, and junD, both acutely and over a 24-h time course. However, whereas carbachol leads only to transient induction of c-jun (maximal at 0.5 h), thrombin induces a biphasic increase in c-jun mRNA--an initial peak at 0.5 h and a second, more-prolonged increase at 12 h. Thrombin but not carbachol also induces a late increase in fra-1 mRNA, which peaks at 12 h. The secondary increase in c-jun mRNA is associated with marked increases in c-Jun protein levels and AP-1 DNA-binding activity. The late induction of c-jun and fra-1 mRNA can be prevented by adding the antagonist hirudin 30 min after thrombin, which results in loss of thrombin-stimulated increases in c-Jun protein, AP-1 DNA-binding activity, and AP-1-mediated transactivation. These findings suggest that rapid and transient conduction of c-fos and c-jun mRNA is insufficient to induce prominent changes in gene transcription, while the sustained increase in c-jun mRNA and perhaps the late induction of fra-1 mRNA are required for generation of AP-1 DNA-binding activity and transactivation through AP-1.

Growth plate injuries: Salter-Harris classification

Fracture of the growth plate is an injury unique to childhood. Most such fractures heal without permanent deformity. A small percentage, however, are complicated by growth arrest and subsequent deformity. The Salter-Harris classification of growth plate injuries aids in estimating both the prognosis and the potential for growth disturbance. The Salter-Harris system classifies growth plate fractures into five groups: type I, fracture through the growth plate; type II, fracture through the growth plate and metaphysis; type III, fracture through the growth plate and epiphysis; type IV, fracture through the growth plate, epiphysis and metaphysis, and type V, crush or compression injury of the growth plate.