摘要:

AbstractClinical and scientific investigations of leukocyte chemotaxis will be greatly aided by an ability to measure quantitative parameters characterizing the intrinsic random motility, chemokinetic, and chemotactic properties of cell populations responding to a given attractant. Quantities typically used at present, such as leading front distances, migrating cell numbers, etc., are unsatisfactory in this regard because their values are affected by many aspects of the assay system unrelated to cell behavioral properties.In this paper we demonstrate the measurement of cell migration parameters that do, in fact, characterize the intrinsic cell chemosensory movement responses using cell density profiles obtained in the linear under‐agarose assay. These parameters are the random motility coefficient, μ, and the chemotaxis coefficient, χ, which appear in a theoretical expression for cell population migration. We propose a priori the dependence of χ on attractant concentration, based on an independent experimental correlation of individual cell orientation bias in an attractant gradient with a spatial difference in receptor occupancy. Our under‐agarose population migration results are consistent with this proposition, allowing chemotaxis to be reliably characterized by a chemotactic sensitivity constant, χ, to which χ is directly proportional. Further, χohas fundamental significance; it represents the reciprocal of the difference in number of bound receptors across cell dimensions required for directional orientation bias.In particular, for the system of human peripheral blood polymorphonuclear neutrophil leukocytes responding to FNLLP, we find that the chemotaxis coefficient is a function of attractant concentration, a, following the expression: χ=χoNTOf(a) S(a) Kd/(Kd+ a)2Where Kdis the FNLLP‐receptor equilibrium dissociation constant and NTOis the total number of cell surface receptors for FNLLP. f(a) is the fraction of surface receptors remaining after down‐regulation, and S(a) is the cell movement speed, both known functions of FNLLP concentration. We find that χ0NTO= 0.2 cm; according to a theoretical argument outlined in the Appendix this means that these cells exhibit 75% orientation toward higher attractant concentration when the absolute spatial difference in bound receptors is 0.0025NTOover 10 μm. (For example, if NTO= 50,000 this would correspond to a spatial difference of 125 bound receptors over 10 μm.) This result can be compared with estimates obtained from visual studies of individual neutrophils.This work thus represents the first satisfactory quantitative measurement of intrinsic chemokinesis and chemotaxis properties using a population migration assay. Of great significance is that our theoretical model permits population migration behavior to be compared to observations of individual cell movement properties. Further, these parameter values can be used to quantitatively elucidate the relative contributions of chemokinesis and chemotaxis in this c

ISSN:0886-1544    

DOI:10.1002/cm.970110102

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractCaenorhabditis eleganssperm are nonflagellated cells that lack actin and myosin yet can form pseudopods to propel themselves over solid substrates. Surface‐attached probes such as latex beads, lectins, and antimembrane protein monoclonal antibodies move rearward over the dorsal pseudopod surface of sessile cells. Using monoclonal antibodies against membrane proteins ofC. eleganssperm to examine the role of localized membrane assembly and rearward flow in crawling movement, we determined that substrates prepared by coating glass with antimembrane protein antibodies, but not naked glass or other nonmembrane‐binding proteins, promote sperm motility. Sperm locomotion is inhibited in a concentration‐dependent fashion when cells are bathed with soluble antimembrane protein monoclonal antibodies but not with antimouse Ig antibodies or a monoclonal antibody against a sperm cytoplasmic protein. Our results suggest thatC. eleganssperm crawl by gaining traction with substrate‐attached ligands via their surface proteins and by using the motor that moves those proteins rearward on unattached cells to pull the entire cell forward. Continuous insertion of new proteins at the front of the cell and their subsequent adhesion to the substrate allows this process to c

ISSN:0886-1544    

DOI:10.1002/cm.970110103

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractTreatment of PtKl cells with 5 mM acrylamide for 4 hr results in alterations in the distribution of keratin filaments within the cells. This effect is reversible within 18 hr. Labeling of PtKl cells with32P demonstrates that there are four phosphorylated keratins, having Mrof 56 k, 53 k, 45 k, and 40 k. Phosphate associated with these polypeptides appears to turn over with a t1/2of 12 hr. Incubation of labeled cells in 5 mM acrylamide results in approximately 50% dephosphorylation of keratins within 2 hr, which is 3 times faster than normal turnover. Recovery of cells from acrylamide is accompanied by rephosphorylation of keratins within 18 hr. Analysis by31P NMR spectroscopy shows that acrylamide treatments are accompanied by a transient decrease in soluble inorganic phosphate. This is followed by a rapid increase in Piwhich gradually returns to normal levels. These studies show a strong correlation between phosphorylation of PtKl cell keratins and morphological response of keratin filaments to acrylamide. These observations suggest that normal distribution of keratin filaments may be, in part, mediated by protein phosphorylation.

ISSN:0886-1544    

DOI:10.1002/cm.970110104

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractPrevious studies with the hagfish, a primitive vertebrate, have shown that the gland thread cells (GTCs) each contain a single thread (∼60 cm long in average‐sized cells) in the form of a concisely coiled cytoskeletal entity destined for export by holocrine secretion. The thread in relatively immature GTCs consists almost entirely of intermediate filaments (IFs) bundled in parallel alignment with far fewer microtubules (MTs). The three thread polypeptides described earlier (α, basic; β acidic; γ, most acidic; each with a Mrof 63–64 kD) are now further evaluated with respect to in vitro assembly, cross‐reactivity with IF polypeptides from higher vertebrates, and peptide sequence homology with known IF polypeptides. The overall results mainly suggest that the hagfish polypeptides are keratinlike substances but lamins or a new type of IF is not ruled out. However, cross‐reactivity is weak with mammalian keratins; the 8–11‐nm filaments formed from mixtures of α and γ in vitro are generally linear rather than the curvilinear structures usually formed by keratin and nonkeratin IFs; and mixtures of α and β tend to yield 9–12‐nm granules or granular strings. Polypeptide analyses on GTCs segregated on the basis of maturational stage show a progressive increase in β/γ values which correlates with cell maturation, but the α/(β+γ) ratios remain near 1. Inasmuch as β and γ have many similar properties, the documented increase in the amount of the β component in aging GTCs might in part be the result of a failure in a posttranslational modification system and may contribute to the ultrastructural changes that accompany thread maturation in preparation for holocrine secretion and subsequent modulation of the

ISSN:0886-1544    

DOI:10.1002/cm.970110105

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractMotility of the marine gliding bacteriumFlexibacter polymorphuswas studied by using microcinematographic techniques. Following adhesion to a glass surface, multicellular filaments and individual cells usually began to glide within a few seconds at a speed of approximately 12 μm per second (at 23°C). Adhesion to the glass surface was evidently mediated by multitudes of extremely fine extracellular fibrils. Gliding velocity was independent of filament length but directly related to electron‐transport activity and substratum temperature in the range 3–35°C. The rate of gliding was inversely related to medium viscosity, suggesting that the locomotor apparatus functions at constant torque. Forward motion was occasionally interrupted by direction reversals, somersaults (observed primarily in single cells of short filaments), or spinning of filaments tethered by one pole. The frequency of direction reversal was found to be an inverse function of filament length. Translational motility was invariably accompanied by sinistral revolution about the longitudinal axis of a filament. The sense and pitch of revolution were constant among filaments of different length. Polystyrene microspheres or India ink particles adsorbed to gliding cells were actively displaced in either direction, their movement tracing either a regular zigzag or helical path along the filament surface. Because microspheres were also observed to move on nonmotile filaments, particle translocation was evidently not obligatorily linked to gliding locomotion. Multiple particles adsorbed to a single filament often moved independently. The data are consistent with a motility mechanism involving limited motion in numerous mechanically independent (yet functionally coordinated) domains on the cell s

ISSN:0886-1544    

DOI:10.1002/cm.970110106

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractDictyostelium discoideumα‐actinin (D.d.α‐actinin) is a calcium and pH‐regulated actin‐binding protein that can cross‐link F‐actin into a gel at a submicromolar free calcium concentration and a pH<7 [Fechheimer, et al., 1982]. We examined mixtures of actin and D.d. α‐actinin at four pH and calcium concentrations that exhibited various degrees of gelation or solation. The macroscopic viscosities of these mixtures were measured by falling ball viscometry (FBV) and compared to the translational diffusion coefficients measured by gaussian spot and periodic‐pattern fluorescence photobleaching recovery (FPR) of both the actin filaments and D.d. α‐actinin. A homogeneous, macroscopic gel was not composed of a static actin network. Instead, the filament diffusion coefficient decreased to ∼65% of the control value. If the D.d. α‐actinin concentration was increased, the solution became inhomogeneous, consisting of domains of higher actin concentration. These domains were often composed of a static actin network. The mobility of D.d. α‐actinin consisted of a major fraction that freely diffused and a minor fraction that appeared immobile under the conditions employed. This suggested that D.d. α‐actinin binding to the actin filaments was static over the time course of measurement (∼5 sec). Under solation conditions, there was no apparent interaction of actin with D.d. α‐actinin. These results demonstrate that (1) actin filaments need not be cross‐linked into an immobile, static array in order to have macroscopic properties of a gel, (2) interpretation of the rheological properties of actin:α‐actinin gels are complicated by spatial heterogeneity of the filament concentration and mobility; and (3) a fraction of D.d. α‐actinin binds statically to actin in undisturbed gels. The implications of these results are discussed in relati

ISSN:0886-1544    

DOI:10.1002/cm.970110107

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

ISSN:0886-1544    

DOI:10.1002/cm.970110101

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY