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D Wessels

Publications and source records attributed to D Wessels.

15 recordsLinked to original sources
PubMed1992

Behavior of Dictyostelium amoebae is regulated primarily by the temporal dynamic of the natural cAMP wave.

The instantaneous velocity plots of Dictyostelium discoideum amoebae responding to natural waves and simulated temporal waves of cAMP with periods of 7 min are highly similar. This similarity has been used to deduce the dynamics of a natural wave crossing an amoeba, and the behavior of amoebae has been characterized during the different phases of a natural wave with a computer-assisted dynamic image analyzing system. During the first approximately 150 sec of the front of a natural wave, cells move persistently toward the aggregation center, with high instantaneous velocity and a decreased frequency of lateral pseudopod formation. During the last 30 sec of the front of the wave and the first 30 sec of the back of the wave, there is a "freeze" in cell shape and a dramatic depression in cell motility, pseudopod formation, and intracellular particle movement. During the last 180 sec of the back of the wave, there is a rebound in pseudopod formation, but it is random in direction and leads to no net cellular translocation. The data suggest that all of the behavior of a cell but orientation during the translocation phase is mediated by the temporal dynamics of the wave. The data also suggest that orientation toward the aggregation center occurs early in the front of the wave and that, once oriented, cells move in a blind fashion during the translocation phase.

Animals↗
PubMed1992

Targeted disruption of the ABP-120 gene leads to cells with altered motility.

The actin-binding protein ABP-120 has been proposed to play a role in cross-linking F-actin filaments during pseudopod formation in motile Dictyostelium amebas. We have tested this hypothesis by analyzing the phenotype of mutant cell lines which do not produce ABP-120. Two different transformation vectors capable of targeted disruption of the ABP-120 gene locus have been constructed using a portion of an ABP-120 cDNA clone. Three independent cell lines with different disruption events have been obtained after transformation of amebas with these vectors. The disruption of the ABP-120 gene by vector sequences results in either the production of a small amount of truncated ABP-120 or no detectable protein at all. The phenotypes of two different clones lacking ABP-120, generated in strains AX3 and AX4, have been characterized and show identical results. ABP-120- cells tend to remain rounder before and after cAMP stimulation, and do not reextend pseudopods normally after rapid addition of cAMP. In addition, ABP-120- cells translocating in buffer exhibit defects in both the rate and extent of pseudopod formation. The amount of F-actin cross-linked into the cytoskeleton after cAMP stimulation of ABP-120- cells is reduced at times when ABP-120 has been shown to be incorporated into the cytoskeleton, and this correlates temporally with the absence of reextension of pseudopods after cAMP stimulation. The instantaneous velocity is significantly reduced both before and after cAMP stimulation in the ABP-120- cells, and the cells show decreased chemotactic efficiency compared to ABP-120+ controls. This phenotype is consistent with a role for ABP-120 in pseudopod extension by cross-linking actin filaments as proposed by the "cortical expansion model" (Condeelis, J., A. Bresnick, M. Demma, C. Dharmawardhane, R. Eddy, A. L. Hall, R. Sauterer, and V. Warren. 1990. Dev. Genet. 11:333-340).

Actins↗
PubMed1992

Discoidin proteins of Dictyostelium are necessary for normal cytoskeletal organization and cellular morphology during aggregation.

The onset of aggregation of bacterially-grown Dictyostelium discoideum amoebae is accompanied by the accumulation of the discoidin proteins. An immunofluorescent analysis demonstrates that discoidin is distributed throughout the cytoplasm, but is excluded from vesicles and nucleoli. There is no indication of either extracellular or membrane localization. Translocating amoebae of mutants lacking discoidin form more dispersed pseudopodial regions at the cell periphery, possess an abnormally centered microtubule organizing center, are blunt rather than elongate, and lack the tapered posterior uropod characteristic of translocating wild-type cells. However, in spite of the loss of the normal elongate morphology, discoidinless mutants translocate with instantaneous velocities and directional persistence comparable to wild-type cells, and they respond normally to the rapid addition of cAMP. These results demonstrate that the discoidin proteins are cytoplasmic components essential for the maintenance of the elongate cell morphology, cytoskeletal organization and the ability to align with other cells during aggregation. However, the elongate morphology is not a requisite for rapid and persistent single cell translocation.

Actins↗
PubMed1991

Myosin IB null mutants of Dictyostelium exhibit abnormalities in motility.

Cellular and intracellular motility are compared between normal Dictyostelium amoebae and amoebae lacking myosin IB (DMIB-). DMIB- cells generate elongated cell shapes, form particulate-free pseudopodia filled with F-actin, and exhibit an anterior bias in pseudopod extension in a fashion similar to normal amoebae. DMIB- cells also exhibit a normal response to the addition of the chemoattractant cAMP, including a depression in cellular and intracellular particle velocity, depolymerization of F-actin in pseudopodia, and a concomitant increase in cortical F-actin. DMIB- cells do, however, form lateral pseudopodia roughly three times as frequently as normal cells, turn more often, and exhibit depressed average instantaneous cell velocity. DMIB- cells also exhibit a decrease in the average instantaneous velocity of intracellular particle movement and an increase in the degree of randomness in particle direction. These findings indicate that if there is functional substitution for myosin IB by other myosin I isoforms, it is at best only partial, with myosin IB being necessary for maintenance of the normal rate and persistence of cellular translocation, suppression of lateral pseudopod formation and subsequent turning, rapid intracellular particle motility, and the normal anterograde bias of intracellular particle movement. Furthermore, it is likely that the behavioral abnormalities observed here for DMIB- cells underlie the delay in the onset of chemotactic aggregation, the increase in the time required to complete streaming, and the abnormalities in morphogenesis exhibited by DMIB- cells.

Actins↗
PubMed1990

Intracellular vesicle movement, cAMP and myosin II in Dictyostelium.

Dictyostelium amoebae were analyzed before and after rapid addition of 10(-6) M cAMP for cellular motility, dynamic shape changes, and intracellular particle movement. Before cAMP addition, amoebae moved in a persistent anterior fashion and were elongate with F-actin localized predominantly in the anterior pseudopod. Intracellular particles moved rapidly and anteriorly. Within seconds after 10(-6) M cAMP addition, cells stopped translocating, pseudopod formation ceased, intracellular particle movement was depressed, and F-actin was lost from the pseudopod and concomitantly relocalized in the cell cortex. After 10 seconds, expansion zones reappeared but were small and no longer anteriorly localized. Vesicle movement partially rebounded but was no longer anteriorly directed. The myosin II null mutant HS2215 exhibited both depressed cellular translocation and vesicle movement. The addition of cAMP to HS2215 cells did not result in any detectable change in the random, depressed movement of particles. The results with HS2215 suggest that myosin II is essential for (1) rapid cellular translocation, (2) cellular polarity, (3) rapid particle movement, (4) anteriorly directed particle movement, and (5) the cAMP response. Electron micrographs suggest that at least half of the particles examined in this study contain in turn smaller membrane bound vesicles or multilamellar membrane bodies. The possible role of these vesicles is discussed.

Actins↗
PubMed1990

Technologically important characteristics of Enterococcus isolates from milk and dairy products.

Enterococcus faecium (54 strains), E. faecalis (40 strains), and E. durans (14) were isolated from various dairy products (raw milk, cream, butter and fermented milk products) during a previous study (Wessels et al., 1988). In this article various characteristics of these isolates, which may have a bearing on their significance in dairy products, have been studied. A large percentage of the identified strains of all three species were able to grow at 7 degrees C. Seventy-six percent of the E. faecium strains, 62% E. faecalis and 50% E. durans strains also showed proteolytic activity at psychrotrophic temperatures. The fact that proteolytic activity could be detected within 2 days at 7 degrees C is significant, since bulk cooled milk is normally held for 3 to 4 days at temperatures between 4 and 7 degrees C at farms or factories prior to processing. This examination confirmed that enterococci are proteolytic rather than lipolytic.

Animals↗
PubMed1990

Myosin II heavy chain null mutant of Dictyostelium exhibits defective intracellular particle movement.

Both cellular motility and intracellular particle movement are compared between normal Dictyostelium amebae of strain AX4 and amebae of a myosin II heavy chain null mutant, HS2215, using the computer assisted "Dynamic Morphology System." In AX4 cells rapidly translocating in buffer, cytoplasmic expansion is apical and the majority of intracellular particles move anteriorly, towards the site of expansion. When these cells are pulsed with 10(-6) M cAMP, the peak concentration of the natural cAMP wave, cells stop translocating and average particle velocity decreases threefold within 2-4 s after cAMP addition. After 8 s, there is a partial rebound both in cytoplasmic expansion and particle velocity, but in both cases, original apical polarity is lost. In HS2215 cells in buffer, both cellular translocation and average particle velocity are already at the depressed levels observed in normal cells immediately after cAMP addition, and no anterior bias is observed in either the direction of cytoplasmic expansion or the direction of particle movement. The addition of cAMP to myosin-minus cells results in no additional effect. The results demonstrate that myosin II is necessary for (a) the rapid rate of intracellular particle movement, (b) the biased anterior directionality of particle movement, and (c) the rapid inhibition of particle movement by cAMP.

Biological Transport↗
PubMed1989

Psychrotrophic, proteolytic and lipolytic properties of Enterobacteriaceae isolated from milk and dairy products.

Most of the Enterobacteriaceae strains (73 out of 75) isolated in a previous study (Wessels et al., 1988) were psychrotrophic on agar plates, with the exception of Enterobacter cloacae strains. The Enterobacteriaceae strains were largely non-proteolytic on milk agar medium although limited numbers of E. cloacae, Serratia rubidaea and Klebsiella oxytoca strains were capable of proteolytic activity at 25 degrees C. The E. cloacae and K. oxytoca strains positive at 25 degrees C were also proteolytic at 7 degrees C. Most of the species tested were non-lipolytic on Victoria blue butterfat agar. The majority of Serratia marcescens and Klebsiella pneumoniae strains and a minority of E. cloacae and K. oxytoca strains, however, were lipolytic on this medium.

Animals↗
PubMed1989

cAMP-mediated inhibition of intracellular particle movement and actin reorganization in Dictyostelium.

Before addition of cAMP, Dictyostelum amoebae rapidly translocating in buffer are elongate, exhibit expansion zones primarily at the anterior end and filamentous actin (F-actin) localization primarily in the anterior pseudopodia. Intracellular particle movement is primarily in the anterior direction, and the average rate of particle movement is roughly five times the rate of cellular translocation. Within seconds after the addition of 10(-6)M cAMP, there is a dramatic suppression of cellular translocation, an inhibition of pseudopod formation, a freeze in cellular morphology, a dramatic depression in intracellular particle movement, loss of F-actin localization in pseudopodia concomitant with relocalization of F-actin in the general cytoplasmic cortex under the plasma membrane, and a doubling of F-actin content. After 10 s, expansion zones are again visible at the cell perimeter, but they no longer are localized in the original anterior portion of the cell. There is a slight rebound in particle movement after 10 s, but particles with persistent tracks now show no directionality towards the original anterior portion of the cell, as they did before cAMP addition. Finally, in parallel with the resumption of peripheral expansion and the small rebound in particle movement, there is a decrease in total cellular F-actin to the untreated level. The pattern of microtubule organization is unaffected by the addition of cAMP.

Actins↗
PubMed1988

"Dynamic Morphology System": a method for quantitating changes in shape, pseudopod formation, and motion in normal and mutant amoebae of Dictyostelium discoideum.

An automated, video-driven system was used to measure approximately 30 parameters of cell motion and accompanying changes in shape. This "Dynamic Morphology System" is based upon the Expertvision Motion Analysis System and is driven by a SUN computer. With the aid of this system, amoebic movement and shape changes were compared for vegetative wild-type Dictyostelium discoideum amoebae and a motility mutant, Mo-1. The measured parameters included speed, angle change, bearing, length, width, roundness, boundary flow, and curvature; and cell behavior was visualized monitoring amoebic tracks, difference pictures, and a newly developed ring expansion plot. Wild-type cells remained elongated, moved continuously and retained polarity throughout migration. In contrast, Mo-1 did not translocate, was round rather than elongated, formed bulges rather than elongated pseudopods, and exhibited no polarity. In contrast to the anterior f-action distribution in wild-type cells, f-actin in Mo-1 was distributed evenly as a shell just under the entire plasma membrane, a distribution consistent with the lack of polar cytoplasmic expansion.

Actins↗
PubMed1988

Cell motility and chemotaxis in Dictyostelium amebae lacking myosin heavy chain.

Dictyostelium amebae have been engineered by homologous recombination of a truncated copy of the myosin heavy chain gene (heavy meromyosin (HMM) cells) and by transformation with a vector encoding an antisense RNA to myosin heavy chain mRNA (mhcA cells) so that they lack native myosin heavy chain protein. In the former case, cells synthesize only the heavy meromyosin portion of the protein and in the latter case they synthesize negligible amounts of the protein. Surprisingly, it was demonstrated that both cell lines are viable and motile. In order to compare the motility of these cells with normal cells, the newly developed computer-assisted Dynamic Morphology System (DMS) was employed. The results demonstrate that the average HMM or mhcA ameba moves at a rate of translocation less than half that of normal cells. It is rounder and less polar than a normal cell, and exhibits a rate of cytoplasmic expansion and contraction roughly half that of normal cells. In a spatial gradient of cAMP, the average ameba of HMM or mhcA exhibits a chemotactic index of +0.10 or less, compared to the chemotactic index of +0.50 exhibited by normal cells. Finally, the initial area, rate of expansion, and final area of pseudopods are roughly half that of normal cells. The five fastest HMM amebae (out of 35 analyzed in detail) moved at an average rate of translocation equal to that of normal amebae, and exhibited an average chemotactic index of +0.34. In addition, the average rate of cytoplasmic flow in fast HMM cells was equal to that of the average normal ameba. However, fast HMM amebae still exhibited the same defects in pseudopod formation that were exhibited by the entire HMM cell population. These results suggest that myosin heavy chain is involved in the "fine tuning" and efficiency of pseudopod formation, but is not essential for the basic behavior of pseudopod expansion.

Actins↗
PubMed1984

A method for the spectrophotometric assay of anaerobic enzymes.

A convenient and inexpensive system for conducting large numbers of spectrophotometric assays at wavelengths between 300 and 750 nm under strictly anaerobic conditions has been developed. Round test tubes or round cuvettes stoppered with either thick black rubber stoppers or thinner red rubber stoppers are used to replace rectangular cuvettes. The round tubes are held in place in the spectrophotometer by a simple metal holder. Additions to the tubes are made by syringe using a specially constructed needle guide to prevent needle bending.

Anaerobiosis↗