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51.
Endopeptidase-24.11 is a 90-kDa surface glycoprotein with the ability to hydrolyze a variety of biologically active peptides. Interest in this enzyme is based on the consensus that it may play a role in the termination of peptide signals in the central nervous system. In the present study, we have investigated the distribution of endopeptidase-24.11 in two nerves of the peripheral nervous system of newborn pigs: the sciatic, composed of a mixture of myelinated and nonmyelinated axons, and cervical sympathetic trunk in which greater than 99% of the axons are nonmyelinated. The endopeptidase was monitored enzymatically, as well as by immunoblotting and immunocytochemistry using mono- and polyclonal anti-endopeptidase antibodies. Endopeptidase-24.11 was detected in both the sciatic nerve and the cervical sympathetic trunk. Membrane preparations from sciatic nerve hydrolyzed 125I-insulin B-chain, and more than 50% of the activity was inhibited by phosphoramidon with an IC50 concentration of 3.2 nM. Moreover, a 90-kDa polypeptide was detected by immunoblotting of sciatic nerve membranes. The type of cells expressing the endopeptidase was determined by immunohistochemistry. In teased nerve preparations, these cells were identified morphologically as myelin- and non-myelin-forming Schwann cells. Endopeptidase-24.11 was also expressed by cultured Schwann cells from sciatic nerve and cervical sympathetic trunk maintained for 3 h in vitro. The presence of endopeptidase-24.11 on the Schwann cell surface raises the possibility of a potential role for the enzyme in nerve development and/or regeneration. 相似文献
52.
Niels C. Krejci Lynne Smith Rebecca Rudd Robert Langdon Joseph McGuire 《In vitro cellular & developmental biology. Animal》1991,27(12):933-938
Summary To investigate the regulation of epithelial differentiation, normal human epidermal keratinocytes were cultured floating on
the surface of culture medium without attachment to a solid substrate. Keratinocytes spread out on the surface of the medium,
proliferated and differentiated either into several flat lacy sheets 1 to 3 cells thick (on medium containing 0.15 mM calcium) or formed one single aggregate of cells from 5 to 15 cells in thickness on medium containing 1.15 mM calcium. The cell aggregates demonstrated a pattern of ordered epithelial differentiation. Levels of progressive differentiation
resembling the structure of normal human epidermis were identified by light microscopy, immunohistochemistry, and electron
microscopy. Differentiation proceeded from cells at the air side toward cells at the medium side with basal appearing cells
on the air side and keratinocytes expressing filaggrin and involucrin on the side toward the medium. These results demonstrate
that organized epithelial differentiation can occur in the absence of extracellular matrix. In contrast with other air-liquid
interface cultures, epithelial differentiation in the absence of extracellular matrix progresses from air towards medium. 相似文献
53.
The structure of the vacuolar ATPase from mesophyll tonoplasts of Mesembryanthemum crystallinum has been studied by electron microscopy using negatively stained specimens of membrane-bound and detergent-solubilized ATPase molecules. We observed a high density of particles on the surface of tonoplast vesicles and “head and stalk” structures on the edge of the membrane, similar to the F0F1-ATPases of mitochondrial and chloroplast membranes. The staining conditions, which are often critical for such small objects, were improved by using methylamine tungstate as negative stain for the membrane-bound ATPase. Compared to other staining solutions generally applied, dissociation of the F1-like enzyme complex from the membrane was best prevented and structural damage of the vesicles was least observed with methylamine tungstate. In freeze-fracture electron microscopy of tonoplast vesicles, where dissociation never occurs since no detergent is used, we also observed “head and stalk” structures on the edge of the membranes, beside many particles on the fracture faces. The detergent-solubilized ATPase forms string-like structures, caused by the aggregation of the hydrophobic membrane-embedded F0-like part of the enzyme. After negative staining the F1-like enzyme complex is arranged alternately along both sides of the string and connected by a narrow stalk. 相似文献
54.
Nutritional requirements for germination and growth of the entomopathogenic fungus Beauveria bassiana are not complex. For germination to occur, a utilizable source of carbon must be present; however, a nitrogen source is needed for continued hyphal growth, otherwise lysis ensues. Compounds that can serve as utilizable carbon-energy sources for germination include glucose, N-acetylglucosamine, glucosamine, chitin, starch, lanolin, hydrocarbons in crude oil, and some longer-chain fatty acids. Both organic and inorganic sources of nitrogen are readily utilized for growth. Conidia undergo active metabolism soon after being placed in a suitable growth medium, indicating that conidia are released from their state of dormancy several hours before emergence of the germ tube can be observed. Because of the nutritional versatility of B. bassiana, this fungus should be able to survive and be infective in several types of natural environments. 相似文献
55.
There is a considerable amount of evidence, confirmed and extended by our studies, in favor of clonal deletion of alloantigen-reactive cells in neonatally induced transplantation tolerance. We have demonstrated in adult mice bearing long-standing skin allografts that lymphocytes specifically reactive with the tolerated H-2 alloantigens are undetectable by mixed lymphocyte and graftversus-host reactions, and in cell-mediated lympholysis. In addition, lymphoid cells capable of suppressing the reactivity of syngeneic normal lymphocytes in these assays similarly escape detection. Moreover, putative precursors of T cells specific for the tolerated antigens cannot be activated polyclonally with concanavalin A (Con A), nor can they be identified among thymocytes ofH-2-tolerant mice. Since the tolerant state can be adoptively transferred with lymphohematopoietic cells to adult, syngeneic mice, we infer that transplantation tolerance is maintained by an active process that achieves specific clonal deletion at an early stage in the ontogeny of alloreactive T lymphocytes. 相似文献
56.
Host defenses in experimental scrub typhus: mapping the gene that controls natural resistance in mice 总被引:25,自引:0,他引:25
M G Groves D L Rosenstreich B A Taylor J V Osterman 《Journal of immunology (Baltimore, Md. : 1950)》1980,125(3):1395-1399
Natural resistance of mice to lethal ifections of Rickettsia tsutsugamushi, strain Gilliam, is controlled by a single, autosomal, dominant gene, which we have designated Ric, with r and s representing the resistant nd susceptible alleles, respectively. Using three sets of recombinant inbred mouse strains (BXD, BXH, and BXJ), the Ric locus was mapped to Chromosome 5 closely linked to the retinal degeneration (rd) locus. This linkage was confirmed by a backcross analysis. Based on the RI strains and the C57BL/6Ty-le congenic strain (the only proven Ric-rd cross-over), we estimate the recombination frequency between Ric and rd to be 0.015. Three presumptive Ric-rd recombinants detected among 93 backcross mice may represent caes of incomplete penetrance of the resistance allele rather than recombination. Analyis of th C57BL/6JTy-le congenic strain indicates that Ric is proximal to rd on Chromosome 5. If so, the correct gene order is Pgm-1-W-Ric-rd-Gus. 相似文献
57.
58.
59.
Chanida Fongsaran Krit Jirakanwisal Natthida Tongluan Allison Latour Sean Healy Rebecca C. Christofferson Kevin R. Macaluso 《PLoS neglected tropical diseases》2022,16(6)
Rickettsia felis is an emerging etiological agent of rickettsioses worldwide. The cosmopolitan cat flea (Ctenocephalides felis) is the primary vector of R. felis, but R. felis has also been reported in other species of hematophagous arthropods including ticks and mosquitoes. Canines can serve as a bacteremic host to infect fleas under laboratory conditions, yet isolation of R. felis from the blood of a vertebrate host in nature has not been realized. Cofeeding transmission is an efficient mechanism for transmitting rickettsiae between infected and uninfected fleas; however, the mechanism of transmission among different orders and classes of arthropods is not known. The potential for R. felis transmission between infected fleas and tick (Dermacentor variabilis) and mosquito (Anopheles quadrimaculatus) hosts was examined via cofeeding bioassays. Donor cat fleas infected with R. felis transmitted the agent to naïve D. variabilis nymphs via cofeeding on a rat host. Subsequent transstadial transmission of R. felis from the engorged nymphs to the adult ticks was observed with reduced prevalence in adult ticks. Using an artificial host system, An. quadrimaculatus exposed to a R. felis-infected blood meal acquired rickettsiae and maintained infection over 12 days post-exposure (dpe). Similar to ticks, mosquitoes were able to acquire R. felis while cofeeding with infected cat fleas on rats infection persisting in the mosquito for up to 3 dpe. The results indicate R. felis-infected cat fleas can transmit rickettsiae to both ticks and mosquitoes via cofeeding on a vertebrate host, thus providing a potential avenue for the diversity of R. felis-infected arthropods in nature. 相似文献
60.
Kyle R. Siegel Muskanjot Kaur A. Calvin Grigal Rebecca A. Metzler Gary H. Dickinson 《Ecology and evolution》2022,12(6)
Crustaceans comprise an ecologically and morphologically diverse taxonomic group. They are typically considered resilient to many environmental perturbations found in marine and coastal environments, due to effective physiological regulation of ions and hemolymph pH, and a robust exoskeleton. Ocean acidification can affect the ability of marine calcifying organisms to build and maintain mineralized tissue and poses a threat for all marine calcifying taxa. Currently, there is no consensus on how ocean acidification will alter the ecologically relevant exoskeletal properties of crustaceans. Here, we present a systematic review and meta‐analysis on the effects of ocean acidification on the crustacean exoskeleton, assessing both exoskeletal ion content (calcium and magnesium) and functional properties (biomechanical resistance and cuticle thickness). Our results suggest that the effect of ocean acidification on crustacean exoskeletal properties varies based upon seawater pCO2 and species identity, with significant levels of heterogeneity for all analyses. Calcium and magnesium content was significantly lower in animals held at pCO2 levels of 1500–1999 µatm as compared with those under ambient pCO2. At lower pCO2 levels, however, statistically significant relationships between changes in calcium and magnesium content within the same experiment were observed as follows: a negative relationship between calcium and magnesium content at pCO2 of 500–999 µatm and a positive relationship at 1000–1499 µatm. Exoskeleton biomechanics, such as resistance to deformation (microhardness) and shell strength, also significantly decreased under pCO2 regimes of 500–999 µatm and 1500–1999 µatm, indicating functional exoskeletal change coincident with decreases in calcification. Overall, these results suggest that the crustacean exoskeleton can be susceptible to ocean acidification at the biomechanical level, potentially predicated by changes in ion content, when exposed to high influxes of CO2. Future studies need to accommodate the high variability of crustacean responses to ocean acidification, and ecologically relevant ranges of pCO2 conditions, when designing experiments with conservation‐level endpoints. 相似文献