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1.
2.
Morphological dispersion of introduced Hawaiian finches: evidence for competition and a Narcissus effect 总被引:2,自引:0,他引:2
Summary Morphological analyses were conducted on finch species introduced to Oahu, Hawaii. As many as 25 species of finches representing four families (Emberizidae, Fringillidae, Ploecidae, Estrildidae) have been introduced to Oahu. Of these, 15 species currently have established wild populations. When compared with pools of 25 and 23 species introduced to Oahu, the 15 surviving species are morphologically overdispersed. This result is consistent with the hypothesis that competition has influenced the outcome of these introductions. We also tested the hypothesis that surviving introduced finches in one habitat (sugarcane fields) were morphologically overdispersed. When the seven surviving finch species found in sugarcane were compared with the pools of 25 and 23 species, they too were morphologically overdispersed. However, when the seven sugarcane species were compared with a species pool consisting of only the surviving 15 species found across Oahu, they were not morphologically overdispersed. This result suggests that morphological analyses of community structure based only on comparisons of assemblages of surviving species may be biased by a Narcissus effect. 相似文献
3.
Intraspecific variation in cellular DNA content was measured in five Coregonus autumnalis spawning populations from the Mackenzie River drainage, Canada, using flow cytometry. The rivers assayed were the Peel, Arctic Red, Mountain, Carcajou, and Liard rivers. DNA content was determined from whole blood preparations of fish from all rivers except the Carcajou, for which kidney tissue was used. DNA content measurements of kidney and blood preparations of the same fish from the Mountain River revealed statistically indistinguishable results. Mosaicism was found in blood preparations from the Peel, Arctic Red, Mountain, and Liard rivers, but was not observed in kidney tissue preparations from the Mountain or Carcajou rivers. The Liard River sample had significantly elevated mean DNA content relative to the other four samples; all other samples were statistically indistinguishable. Significant differences in mean DNA content among spawning stocks of a single species reinforces the need for adequate sample sizes of both individuals and populations when reporting "C" values for a particular species. 相似文献
4.
R M Bannerman M J Marinello M M Cohen C Lockwood 《American journal of human genetics》1971,23(3):281-288
5.
Summary A phase contrast and time lapse cinematographic study of normal mouse sciatic nerve cultured in vitro was made. The Rose chamber and chicken plasma clot methods were employed. The growth was characterized by three basic cell types: a spindle-shaped cell with a bulging nucleus, a racket-shaped cell with a short wide fan-shaped process and an opposite filiform process, and a kite-shaped cell with abundant ectoplasm. The spindle-shaped cells exhibited a pulsatile rhythmic activity. The rhythm of contraction varied from two to eighteen minutes. No contractile activity was observed in the case of the racket-shaped cells nor in the kite-shaped cells. The spindle-shaped cells were thought to be Schwann cells, the kite-shaped cells were considered of a fibroblastic nature, whereas no source could be found for the racket-shaped cells, although the perineurium was considered as a possible origin. The cultures were maintained up to 80 days, but at no time were phagocytes, observed. With the methods employed no transformation of cells from one type to another took place, and the Schwann cells did not transform themselves into phagocytes.This work was supported in part by grant P-405A from the American Cancer Society and by NIH grant NB-06391-02. 相似文献
6.
C D Robertson M J North B C Lockwood G H Coombs 《Journal of general microbiology》1990,136(5):921-925
A method comprising enzyme separation by SDS-PAGE and subsequent use of peptidyl aminomethylcoumarins as substrates has been used to study proteinases of the protozoan parasite Trypanosoma brucei. The application of this method has allowed investigation of the substrate specificities of individual proteinases in cell lysates without the need for enzyme purification. The results show that T. brucei contains a group of cysteine proteinases, probably four in number, with substrate and inhibitor specificities similar to those of cathepsin L. A second group of proteinases, larger enzymes with significantly different substrate specificities and sensitivity to inhibitors, was also detected. Peptidyl diazomethanes inhibited the cysteine proteinases and also parasite growth, offering promise that peculiarities in the substrate specificity of trypanosomal cysteine proteinases could be exploited by compounds of this type. 相似文献
7.
K. Nomata K.-S. Kang T. Hayashi D. Matesic L. Lockwood C. C. Chang J. E. Trosko 《Cell biology and toxicology》1996,12(2):69-78
Based on the concern of organochlorides in the environment and in human tissue, this study was designed to determine whether various noncytotoxic levels of heptachlor and heptachlor epoxide could inhibit, reversibly, gap junctional intercellular communication in human breast epithelial cells (HBEC). Cytotoxicity and gap junctional intercellular communication (GJIC) were evaluated by lactate dehydrogenase assay and fluorescence redistribution after photobleaching analysis, respectively. Both heptachlor and heptachlor epoxide were noncytotoxic up to 10 μg/ml. At this concentration, heptachlor and heptachlor epoxide inhibited GJIC of normal human breast epithelial cells after 1 h treatment. Within a 24 h treatment with heptachlor and heptachlor epoxide at 10 μg/ml, recovery of GJIC had not returned. GJIC completely recovered after a 12 h treatment of 1 μg/ml heptachlor epoxide, but it did not recover after a 24 h treatment of 1 μg/ml heptachlor. RT-PCR and Western blots were analyzed to determine whether the heptachlor or heptachlor epoxide might have altered the steady-state levels of gap junction mRNA and/or connexin protein levels or phosphorylation state. No significant difference in the level of connexin 43 (Cx43) message between control and heptachlor-treated cells was observed. Western blot analyses showed hypophosphorylation patterns in cells treated with 10 μg/ml heptachlor and heptachlor epoxide for 1 h with no recovery within 24 h. Immunostaining of Cx43 protein in normal HBEC indicated that heptachlor and heptachlor epoxide caused a loss of Cx43 from the cell membranes at noncytotoxic dose levels. Taken together, these results suggest that heptachlor and heptachlor epoxide can alter GJIC at the post-translational level, and that, under the conditions of exceeding a threshold concentration in the breast tissue containing ‘initiated’ cells for a long time and not being counteracted by anti-tumor-promoting chemicals, they could act as breast tumor promoters. 相似文献
8.
Max R. Taylor Lucy A. Lawson Virginia G. Lockard William R. Lockwood 《Mycopathologia》1984,88(2-3):173-180
Electron microscopic examination of yeasts of Blastomyces dermatitidis, exposed in vitro to concentrations of lidocaine that occur when the drug is used for topical anesthesia, showed that lidocaine rapidly damaged intracellular structures. The extent of damage was dependent on the concentration of drug and length of exposure. The observed ultrastructural changes were very similar to those reported for other drugs that directly damage membranes. This relationship suggests that the antifungal effect of lidocaine is the result of direct membrane damage. 相似文献
9.
The main cysteine proteinases of the amastigote form of Leishmania mexicana mexicana were partially purified by gel filtration and ion exchange chromatography. The latter procedure resulted in the separation of some individual cysteine proteinases, as demonstrated by gelatin-sodium dodecyl sulphatepolyacrylamide gel electrophoresis. Fractions containing the partially purified proteinases rapidly hydrolysed L-leucine methyl ester to leucine. The activity towards this compound co-eluted with and resembled the parasite's cysteine proteinase activity. The results suggest that amastigotes of L.m.mexicana are susceptible to L-leucine methyl ester because this compound is rapidly hydrolysed by cysteine proteinases that occur in abundance in the megasomes of this stage. 相似文献
10.
Protein turnover and proliferation. Turnover kinetics associated with the elevation of 3T3-cell acid-proteinase activity and cessation of net protein gain. 总被引:3,自引:2,他引:1 下载免费PDF全文
1. At least 95% of the total protein of A31-3T3 cell cultures undergoes turnover. 2. First-order exponential kinetics were used to provide a crude approximation of averaged protein synthesis, Ks, degradation, Kd, and net accumulation, Ka, as cells ceased growth at near-confluent density in unchanged Dulbecco's medium containing 10% serum. The values of the relationship Ka = Ks - Kd were : 5%/h = 6%/h - 1%/h in growing cells, and 0%/h = 3%/h - 3%/h in steady-state resting cells. 3. As determined by comparison of the progress of protein synthesis and net protein accumulation, the time course of increase in protein degradation coincided with the onset of an increase in lysosomal proteinase activity and decrease in thymidine incorporation after approx. 2 days of exponential growth. 4. After acute serum deprivation, rapid increases in protein degradation of less than 1%/h could be superimposed on the prevailing degradation rate in either growing or resting cells. The results indicate that two proteolytic mechanisms can be distinguished on the basis of the kinetics of their alterations. A slow mechanism changes in relation to proliferative status and lysosomal enzyme elevation. A prompt mechanism, previously described by others, changes before changes in cell-cycle distribution or lysosomal proteinase activity. 5. When the serum concentration of growing cultures was decreased to 1% or 0.25%, then cessation of growth was accompanied by a lower steady-state protein turnover rate of 2.0%/h or 1.5%/h respectively. When growth ceased under conditions of overcrowded cultures, or severe nutrient insufficiency, protein turnover did not attain a final steady state, but declined continually into the death of the culture. 相似文献