ISSN:0892-6638    

DOI:10.1096/fasebj.8.11.8070627

出版商:Wiley    

年代:1994

数据来源: WILEY

ISSN:0892-6638    

DOI:10.1096/fasebj.8.11.8070628

出版商:Wiley    

年代:1994

数据来源: WILEY

摘要:

With the development of sensitive and specific fluorescent indicators, modern laser scanning microscopies enable visualization and measurement of submicron, dynamic processes inside living cells and tissues. Here we describe the working principles of new, nonlinear laser microscopies based on two‐photon molecular excitation. In these techniques, a pulsed laser produces peak photon densities high enough that when focused into an appropriate medium, excitation by photon energy combinations can occur. For example, two red photons interacting simultaneously with a fluorescent molecule can excite within it a UV electronic transition, one corresponding to twice the energy of each single photon. Because the amount of two‐photon excitation depends on the square of the local illumination intensity, this process exhibits a unique localization to the diffraction‐limited spot of the beam focus. Elsewhere along the beam, excitation of background and photodamage is virtually nonexistent. Focal point localization of two‐photon excitation lends to all visualization, measurement, and photopharmacology studies an intrinsic, three‐dimensional resolution. We describe some preliminary biological applications, specifically, imaging of vital DNA stains in developing cells and embryos, imaging of cellular metabolic activity from NADH autofluorescence, spatially resolved measurements of cytoplasmic calcium ion activity, and optically induced micropharmacology using caged bioeffector molecules.—Williams, R. M., Piston, D. W., Webb, W. W. Two‐photon molecular excitation provides intrinsic three‐dimensional resolution for laser‐based microscopy and microphotochemistry.FASEB J.8: 804‐813; 1994.

ISSN:0892-6638    

DOI:10.1096/fasebj.8.11.8070629

出版商:Wiley    

年代:1994

数据来源: WILEY

摘要:

Calpain, calcium‐activated neutral protease, stands as a unique receptor for calcium signals in biological systems; its activation leads to irreversible proteolytic processing of substrate proteins, modifying cellular situations in a manner distinct from that of reversible processes including the phosphorylation‐dephosphorylation reactions. Because the enzyme participates not only in normal intracellular signal transduction cascades but also in various pathological states including ischemia, calpain research has attracted tremendous interest in wide areas of life sciences in both basic and clinical terms. This review will address the new perspectives evoked by recent discoveries since 1990. Molecular biological studies have established that calpain in fact constitutes a large family of distinct isozymes differing in structure and distribution, whereas an increasing number of reports describe physiological‐pathological involvement of calpain. Another major accomplishment is the technical breakthrough allowing spatial resolution of calpain action presenting a clearer in vivo picture of how calpain acts in cells and tissues.— ‐Saido, T. C., Sorimachi, H., Suzuki, K. Calpain: new perspectives in molecular diversity and physiological‐pathological involvement.FASEB J.8: 814‐822; 1994.

ISSN:0892-6638    

DOI:10.1096/fasebj.8.11.8070630

出版商:Wiley    

年代:1994

数据来源: WILEY

摘要:

Massive cell migration, proliferation, phenotypic differentiation, and enhanced biosynthetic activities characterize the sites of wound healing and fibrosis. Regulation of cellular functions by extracellular matrix, which consists of a dynamic assemblage of a variety of interacting molecules capable of reorganization in response to endogenous and exogenous stimuli, represents a fundamental epigenetic mechanism regulating cellular behavior and phenotype. Interactions of the individual components of extracellular matrix with specific cell surface molecules, integrin receptors, and proteoglycans initiate a cascade of signal transduction leading to varied short‐term or persistent cellular responses. Extracellular matrix also serves as an important reservoir of cytokines and growth factors, thus modulating the action of a host of potent biological response modifiers by their selective, local accumulation and release. Currently known mechanisms by which extracellular matrix modulates different facets of the process of tissue remodeling after injury, which culminate either in normal wound repair or fibrosis, are discussed.— Raghow, R. The role of extracellular matrix in postinflammatory wound healing and fibrosis.FASEB J.8: 823‐831; 1994.

ISSN:0892-6638    

DOI:10.1096/fasebj.8.11.8070631

出版商:Wiley    

年代:1994

数据来源: WILEY

摘要:

Germinal centers in lymphoid tissue are the sites of generation of memory B cells undergoing isotype switching and somatic mutation in their Ig genes. Their formation cannot be induced by stimuli other than immunogenic ones. It seems likely that in the function and possibly also in the formation of germinal centers, one important factor is the localization of immune complexes with fixed complement on the surface of follicular dendritic cells. CD4+T cells, located primarily in the “apical light zones” of the centers, are necessary for germinal center formation. However, their exact role in the process needs clarification, as both cell to cell contact and cytokine production could be involved at different stages of the germinal center generation. These T cells are usually specific for the antigen inducing the germinal center, but they may sometimes respond to other surface components on the B cell surface. In view of the possible stimulatory role of CD4+T cells in follicular center‐derived lymphomas, the functional significance of these T cells in germinal center proliferation is important to unravel. The B cells in germinal centers proliferate extremely rapidly, especially those located in the “dark zones.” Many of them undergo apoptosis, particularly in the “basal light zones.” The microenvironment of these centers is well suited to the task of expanding and selecting memory B cells of high affinity for the inducing antigen. The interactions of the proliferating B cells with dendritic cells and T cells, unevenly distributed in the various zones of the germinal center, are thought to determine which cells deserve rescue from apoptosis and induction to differentiation into small resting memory B cells. The memory B cells that emerge from the germinal center bear sIg, usually of “switched” isotype, and exhibit somatic mutations in the variable regions of their rearranged Ig genes.— Thorbecke, G. J., Amin, A. R., Tsiagbe, V. K. Biology of germinal centers in lymphoid tissue.FASEB J.8: 832‐840; 1994.

ISSN:0892-6638    

DOI:10.1096/fasebj.8.11.8070632

出版商:Wiley    

年代:1994

数据来源: WILEY

摘要:

Classical signal transduction theory revolves around the premise that the role of membrane receptors is to transfer the signal represented by ligand binding from the external cell surface across the membrane to within the cell. Other components of the signaling cascade such as second‐messenger molecules and kinases then convey the signal from the cytoplasm to the nucleus to effect changes in gene expression. Membrane receptor endocytosis is seen as part of the cellular down‐regulation and desensitization apparatus rather than as having an active signaling function. Evidence is mounting, however, that polypeptide ligands and their membrane receptors may have an important additional signaling role within the cell including the nucleus. Several ligands such as those of the platelet‐derived and fibroblast growth factor classes have been found not only to localize in the nucleus, but also to possess sequences similar to the nuclear localization signal of the simian virus SV40 large T antigen. In most cases where they have been examined, these sequences appear to be both functional in nuclear targeting and essential for full signaling activity. The implication is that subsequent to internalization, polypeptide ligands and/or their receptors may translocate to the nucleus and participate directly in regulating gene expression.— Jans, D. A. Nuclear signaling pathways for polypeptide ligands and their membrane receptors?FASEB J.8: 841‐847; 1994.

ISSN:0892-6638    

DOI:10.1096/fasebj.8.11.8070633

出版商:Wiley    

年代:1994

数据来源: WILEY

摘要:

Chitin, a β‐(1 → 4) polymer of N‐acetyl‐glucosamine, is an important constituent of fungal cell walls. This polymer is synthesized by the incorporation of N‐acetyl‐D‐glucosamine units from the precursor UDP‐N‐acetyl‐D‐glucosamine (UDP‐GlcNAc) in a reaction catalyzed by chitin synthase. In the aquatic fungusBlastocladiella emersonii, chitin, the major component of the cell wall, is synthesized and incorporated in the cell surface of the free‐swimming zoospore during the abrupt transition from this wall‐less cell to the sessile, wall‐containing cyst. Studies with cycloheximide indicate that chitin synthesis occurs in the apparent absence of protein synthesis, and thus posttranslational controls presumably regulate the cell wall biogenesis during encystment. Glutamine: fructose 6‐phosphate amidotransferase, first enzyme of the hexosamine biosynthetic pathway, was found to play a central role in the regulation of chitin synthesis in this fungus. This enzyme exists in two forms, which are interconvertible by phosphorylation or dephosphorylation of serine residues. It is allosterically inhibited in the phosphorylated form, as it is in the zoospore, by UDP‐Glc∗∗∗NAc. In addition, UDP‐GlcNAc inhibits the dephosphorylation of amidotransferase catalyzed by protein phosphatases 2A and 2G. Thus, UDP‐Glc∗∗∗NAc plays a dual role in hexosamine and chitin synthesis in zoospore: it not only inhibits the phosphorylated form of the enzyme but also prevents its dephosphorylation. The available data suggest that substrate availability plays a role in the control of chitin synthesis during zoospore differentiation.— Costa Maia, da José Carlos. Hexosamine and cell wall biogenesis in the aquatic fungusBlastocladiella emersonii. FASEB J.8: 848‐853; 1994.

ISSN:0892-6638    

DOI:10.1096/fasebj.8.11.8070634

出版商:Wiley    

年代:1994

数据来源: WILEY

摘要:

The pathogenesis of fibrotic disorders is similar regardless of the tissues involved. Inflammatory leukocytes infiltrate the site triggered by chemotactic and activating mediators. This is followed by the elaboration of cytokines that directly and indirectly induce the proliferation of fibroblasts and endothelial cells and the deposition of extracellular matrix (ECM). In the absence of inhibitory signals, the continued production of these mediators sustains the connective tissue accumulation, which results in permanent alteration in tissue structure and function.— Kovacs, E. J., DiPietro, L. A. Fibrogenic cytokines and connective tissue production.FASEB J.8: 854‐861; 1994.

ISSN:0892-6638    

DOI:10.1096/fasebj.8.11.7520879

出版商:Wiley    

年代:1994

数据来源: WILEY

摘要:

The current studies were designed to isolate a cDNA encoding the control mouse renal sodium phosphate (NaVPi) transporter and to determine mRNA levels encoding this transporter in control and (Hyp) mice. A 2.4 kb cDNA was isolated from a control mouse kidney cDNA library using a PCR‐amplified 850 base pair (bp) fragment of rat cDNA. The cDNA encoding the mouse renal NaVPi transporter shows sequence similarity to the rat and human Na+VPitransporters. The predicted protein exhibits 98% and 91% amino acid sequence identity with the rat and human proteins, respectively. A cRNA was synthesized from the cDNA and showed an expression of sodium‐dependent phosphate transport inXenopus laevisoocytes. Northern blot analysis of renal poly(A)+RNA from (Hyp) and control mice showed a threefold decrease in mRNA level in the (Hyp) mice compared with control mice. In situ hybridization analysis localizes the Na+/Pitransporter message to the renal proximal tubule, with message levels distinctly lower in the (Hyp) mouse. Also, genomic Southern blotting suggests that the gene encoding the sodium phosphate transporter is structurally identical in the control and (Hyp) mice. These studies suggest that we have cloned the cDNA encoding the renal Na+/Pitransporter in the control [C57BL/ 6J+/ymale] mouse, localized the message to the renal proximal tubule, and shown that the mRNA level encoding the renal NaVPi transporter is decreased in the hypophosphatemic mouse.—Collins, J. F., Ghishan, F. K. Molecular cloning, functional expression, tissue distribution, and in situ hybridization of the renal sodium phosphate (Na+/Pi) transporter in the control and hypophosphatemic mouse.FASEB J.8: 862‐868; 1994.

ISSN:0892-6638    

DOI:10.1096/fasebj.8.11.8070635

出版商:Wiley    

年代:1994

数据来源: WILEY