The response of murine intestinal crypts to short-range promethium-147 beta irradiation: deductions concerning clonogenic cell numbers and positions

An exteriorized loop of mouse intestine was exposed to 147Pm low-energy electrons, where the dose rate decreased by a factor of 5 from the base of the crypt to the top of the proliferative zone. A crypt survival curve was obtained, expressed in terms of exposure time. The shape of the curve was interpreted in terms of survival parameters for colony-forming cells (clonogens) derived using 137Cs gamma rays and the depth-dose curve measured for 147Pm electrons. It is concluded that the shape of the crypt survival curve using 147Pm electrons is inconsistent with the notion of either the presence of a large number of clonogens or a small number near the top of the proliferative zone. A computer fitting procedure showed that the best agreement between predicted and observed curves was achieved with 2.7 +/- 0.5 clonogens at cell position 5.6 +/- 0.6, in the putative stem-cell zone.     

Mucosal epithelial cells and Langerhans cells are targets for infection by the immunosuppressive type D retrovirus simian AIDS retrovirus serotype 1

Simian acquired immune deficiency syndrome (SAIDS) caused by the type D retrovirus SRV-1 results in opportunistic infections and a spectrum of oral lesions similar to those seen in humans with AIDS. To better understand the pathogenesis of these oral lesions we have retrospectively examined the oral mucosa from ten rhesus monkeys that died with SAIDS and prospectively examined the oral mucosa of ten additional animals inoculated with SRV-1 to determine at what time, and in what cells SRV-1 infection of the oral mucosa occurs. Using single and double label immunohistologic techniques, and electron microscopy we detected SRV-1 in clusters of oral epithelial cells and rare Langerhans cells as early as 1 month postinoculation.     

SecA protein, a peripheral protein of the Escherichia coli plasma membrane, is essential for the functional binding and translocation of proOmpA.

We have reconstituted protein translocation across plasma membrane vesicles of Escherichia coli using purified proOmpA and trigger factor, a 63 kd soluble protein. Treatment of membrane vesicles with urea inactivates them for translocation unless a factor present in cytoplasmic extracts is added during the translocation reaction. Sedimentation analysis showed that the stimulatory activity is of distinctly higher mol. wt than trigger factor. Cytoplasmic extracts from a strain that greatly overproduces the SecA protein are highly enriched in the stimulatory activity for untreated membranes and restore translocation to urea-treated membranes, suggesting that this protein is the stimulatory factor. This assay was used to monitor the isolation of SecA protein from the overproducing strain. The purified protein is soluble, yet binds peripherally to membranes with high affinity and supports translocation. Using pure proOmpA, SecA protein, trigger factor and urea-treated membranes, the protein export process was resolved into binding and translocation steps. We find that proOmpA binds to membrane vesicles with or without SecA protein, but that translocation only occurs when SecA was bound prior to proOmpA.     

Melanin accelerates the tyrosinase-catalyzed oxygenation of p-hydroxyanisole (MMEH)

Although pigment melanin has long been though of as "inert," recent work has attested to its chemical reactivity. In this communication, we report that either commercial synthetic melanin prepared by persulfate oxidation of tyrosine ("Sigma melanin") or sepia melanin extracted from cuttlefish markedly accelerates the in vitro oxygenation of p-hydroxyanisole (MMEH), catalyzed by mushroom or B-16 melanoma tyrosinase. Kinetics of 4-methoxy-1,2-benzoquinone formation (lambda max = 413 nm) or of molecular O2 uptake were biphasic, with an initial slow rate ("lag time") followed by a fast linear increase. The biphasic response reflects an initial slow hydroxylation followed by a fast dehydrogenation. Added melanin markedly decreased the lag time but had little effect on subsequent dehydrogenation. Similar effects were observed for tyrosine itself. A complex between MMEH and melanin appears to be the "active" species in these reactions. The results indicate that melanin acts as an electron conduit, which accepts electrons from the substrate and transfers them to tyrosinase. The magnitude of the effect depends on the type of melanin as well as on its oxidation state. Kinetic analysis indicates that both melanins are very efficient at transferring electron to tyrosinase, and that Sigma melanin is roughly threefold more efficient than sepia melanin. The qualitative similarity of reaction between the synthetic and "natural" melanins suggests that the former may serve as a first approximation to the in vivo situation. On the other hand, the observed quantitative differences and the sensitivity of these results to the chemical state of melanin suggests that this methodology might eventually be adapted as a non-destructive probe of melanin in situ.(ABSTRACT TRUNCATED AT 250 WORDS)     

Histochemical and microbiochemical demonstration of reduced pyruvate kinase activity in thioacetamide-induced neoplastic nodules of rat liver

A new method for the histochemical demonstration of pyruvate kinase (PK) activity was developed using a semi-permeable membrane and ATP-dependent phosphorylation of glucose coupled with tetrazolium reduction via glucose-6-phosphate dehydrogenase (G6PD) in order to investigate normal liver tissue and neoplastic hepatic nodules induced by thioacetamide (TAA). A series of control reactions and comparison with microbiochemical analysis of microdissected lyophilised material were used to determine the specificity of the reaction. In agreement with earlier reports, an activity gradient in control liver decreasing from zone 3 to zone 1 was apparent both histochemically and after biochemical analysis. Liver neoplastic nodules induced by 25 weeks dietary thioacetamide administration and characterized by increased G6PD demonstrated a clear decrease in PK activity. In contrast, epithelial cells within areas of cholangiocellular tumour development were characterized by a strong increase. Comparison of the results with immunohistochemical and biochemical data from the literature indicate that the specific histochemical method described will be of great assistance in future assessment of disease and physiological alteration in activity of this key enzyme of glycolysis.     

Effect of aortic arterial catheterization on tissue glycogen content

Measurements of hemodynamics and blood metabolites in rats are often made by insertion of a small polyethylene (PE-50) catheter into the aorta via the carotid artery. Although the effect of this type of procedure on animal body weight has been described, little information exists regarding the quantitative and temporal effects of this procedure on liver and skeletal muscle glycogen concentration. Relative to the control group (group C), liver glycogen concentration was reduced by 56% 24 h after catheterization (group CN). With respect to liver glycogen concentration, it was apparent that a postcatheterization recovery period of variable duration (2-8 days; group CNR) based on attainment of a normal food consumption-to-body weight ratio (FdWt/BdWt) was more effective than was a fixed 6-day recovery period (group CN6). This was probably due to the large between-animal variability in recovery times required to reach normal FdWt/BdWt values. After aortic catheterization, FdWt/BdWt was a reasonable predictor of postprocedural liver (y = 2,601x + 43.9; r = 0.72; P less than 0.01) and diaphragm muscle glycogen concentration (y = 146.3x + 14.0; r = 0.57; P less than 0.05). Aortic catheterization did not affect the glycogen concentration in the other skeletal muscles examined. Since the results of certain types of experiments can be significantly influenced by liver glycogen concentration, the use of FdWt/BdWt on 24-h food intake as a general indicator of recovery after instrumentation via aortic catheterization is proposed.     

The effects of low levels of chloramphenicol and methotrexate on somatic embryogenesis inCitrus

Summary The effects of the antibiotics methotrexate and chloramphenicol on somatic embryogenesis inCitrus were evaluated. Relatively low levels (0.1 to 1.0 μg/ml) of these antibiotics did not inhibit embryo production from undeveloped ovules of ‘Key’ lime [C. aurantifolia) (Christm.) Swing.]. Surprisingly, both antibiotics induced the formation of embryogenic callus in these cultures. This is usually a rare event in cultures of undevelopedCitrus ovules, and ‘Key’ lime is especially recalcitrant. The effects of these antibiotics on embryogenic callus appeared to be limited to the induction stage, because there was no consistent effect, either stimulatory or inhibitory, on established, lines of embryogenic callus. Florida Agricultural Experiment Station Journal Series No. 8958. This research was supported in part by a grant to Moore and Cline from the Competitive Grants Office of the SEA, USDA (85-CRCR-1-1623).     

The relationship between species richness and standing crop in wetlands: the importance of scale

One of the few important empirical generalizations regarding herbaceous plant systems has been the demonstration that species richness is related to standing crop with maximum richness occurring at moderate levels of standing crop. This relationship is normally demonstrated by comparing among vegetation types (i.e., vegetation with different dominants). We undertook this study to test whether the species richness-standing crop relationship was evident at a finer-grained level of organization, the within vegetation type level. Fifteen wetland sites were sampled in eastern Canada and species richness and standing crop determined in each of 224 0.25 m² quadrats. Each site was relatively homogeneous in terms of the dominant species present and were therefore categorized as single vegetation types. However, as a group, the sites comprised a wide range of vegetation types.A second order polynomial regression indicated a significant bitonic relationship between species richness and standing crop at the among-vegetation types scale, that is, when all 15 sites were combined. At the within-vegetation type level, however, no significant relationships were observed (p>0.05). The results indicate that the model of species richness proposed by Grime has predictive power at a coarse-grained level of organization, among vegetation types, but does not survive the transition to a finer-grained level of organization, the within vegetation type level. Therefore, the higher level processes which structure species richness patterns among vegetation types are not the same processes which determine richness patterns within a vegetation type.     

Multiparameter DNA flow cytometry of keratoacanthoma.

Keratoacanthomas (KAs) are rapidly growing cutaneous lesions that frequently look much like well-differentiated squamous cell carcinomas (SCCs) but spontaneously regress. It is uncertain whether KA is a reactive hyperplastic lesion that mimics a neoplasm or a true (but defective) neoplasm that cannot sustain progressive growth. To address this question, we performed DNA flow cytometric analysis on 14 KAs and 10 cutaneous SCCs for comparison. By multiparameter DNA flow cytometry using forward scatter and orthogonal scatter, 10 KAs and 4 SCCs had peridiploid DNA aneuploid populations (DNA indices of 1.03-1.14), and 2 SCCs had grossly aneuploid populations (DNA index, 1.69 and 2.33). Our data thus support aneuploidy in KAs. It is argued that KA is a true neoplasm.