dictyNews

Electronic Edition

Volume 44, number 33

November 23, 2018



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Abstracts

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Comparative Biology of Centrosomal Structures in Eukaryotes



Ralph Gräf



Department of Cell Biology, University of Potsdam, Karl-Liebknecht-Str. 

24-25, 14476 Potsdam-Golm, Germany





Cells, 7, 11, doi: 10.3390/cells7110202



The centrosome is not only the largest and most sophisticated protein 

complex within a eukaryotic cell, in the light of evolution, it is also one 

of its most ancient organelles. This special issue of "Cells" features 

representatives of three main, structurally divergent centrosome types, 

i.e., centriole-containing centrosomes, yeast spindle pole bodies (SPBs), 

and amoebozoan nucleus-associated bodies (NABs). Here, I discuss 

their evolution and their key-functions in microtubule organization, 

mitosis, and cytokinesis. Furthermore, I provide a brief history of 

centrosome research and highlight recently emerged topics, such as 

the role of centrioles in ciliogenesis, the relationship of centrosomes and 

centriolar satellites, the integration of centrosomal structures into the 

nuclear envelope and the involvement of centrosomal components in 

non-centrosomal microtubule organization.





submitted by:  Ralph Gräf [[log in to unmask]]

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Parallel signaling pathways regulate excitable dynamics differently for 

pseudopod formation in eukaryotic chemotaxis



Yuki Tanabe, Yoichiro Kamimura, Masahiro Ueda





Journal of Cell Science, in press



In eukaryotic chemotaxis, parallel signaling pathways regulate the 

spatiotemporal pseudopod dynamics at the leading edge of a motile 

cell through characteristic dynamics of an excitable system; however, 

differences in the excitability and the physiological roles of individual 

pathways remain to be elucidated. Here we found that two different 

pathways, soluble guanylyl cyclase (sGC) and phosphatidylinositol 

3-kinase (PI3K), exhibited similar all-or-none responses but different 

refractory periods by simultaneous observations of their excitable 

properties. Due to the shorter refractory period, sGC signaling 

responded more frequently to chemoattractants, leading to 

pseudopod formation with higher frequency. sGC excitability was 

regulated negatively by its product, cGMP, and cGMP-binding 

protein C (GbpC) through the suppression of F-actin polymerization, 

providing the underlying delayed negative feedback mechanism for 

the cyclical pseudopod formation. These results suggest that parallel 

pathways respond on different time-scales to environmental cues for 

chemotactic motility based on their intrinsic excitability. Key words: 

cGMP signaling, chemotaxis,





submitted by:  Yoichiro Kamimura [[log in to unmask]]

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Chemoattractant receptors activate, recruit and capture G proteins 

for wide range chemotaxis



Yukihiro Miyanaga, Yoichiro Kamimura, Hidekazu Kuwayama, 

Peter N.Devreotes, Masahiro Ueda





Biochemical and Biophysical Research Communications, in press



The wide range sensing of extracellular signals is a common feature 

of various sensory cells. Eukaryotic chemotactic cells driven by GPCRs 

and their cognate G proteins are one example. This system endows the 

cells directional motility towards their destination over long distances. 

There are several mechanisms to achieve the long dynamic range, 

including negative regulation of the receptors upon ligand interaction 

and spatial regulation of G proteins, as we found recently. However, 

these mechanisms are insufficient to explain the 105-fold range of 

chemotaxis seen in Dictyostelium. Here, we reveal that the receptor-

mediated activation, recruitment, and capturing of G proteins mediate 

chemotactic signaling at the lower, middle and higher concentration 

ranges, respectively. These multiple mechanisms of G protein dynamics 

can successfully cover distinct ranges of ligand concentrations, resulting 

in seamless and broad chemotaxis. Furthermore, single-molecule 

imaging analysis showed that the activated G-alpha subunit forms an 

unconventional complex with the agonist-bound receptor. This complex 

formation of GPCR-G-alpha increased the membrane-binding time of 

individual G-alpha molecules and therefore resulted in the local 

accumulation of G-alpha. Our findings provide an additional chemotactic 

dynamic range mechanism in which multiple G protein dynamics positively 

contribute to the production of gradient information.





submitted by:  Yoichiro Kamimura [[log in to unmask]]

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Diversity of Free-Living Environmental Bacteria and Their Interactions 

With a Bactivorous Amoeba



Debra A. Brock 1*, Tamara S. Haselkorn 1, Justine R. Garcia 1, Usman 

Bashir 1,Tracy E. Douglas 1, Jesse Galloway 2, Fisher Brodie 2, David 

C. Queller 1, and Joan E. Strassmann 1



1 Queller/Strassmann Laboratory, Washington University in St. Louis, 

Department of Biology, St. Louis, MO, United States,

2 Mountain Lake Biological Laboratory, University of Virginia, Mountain 

Lake, VA, United States





Frontiers in Cellular and Infection Microbiology, in press



A small subset of bacteria in soil interact directly with eukaryotes. Which 

ones do so can reveal what is important to a eukaryote and how eukaryote 

defenses might be breached.  Soil amoebae are simple eukaryotic 

organisms and as such could be particularly good for understanding how 

eukaryote microbiomes originate and are maintained. One such amoeba, 

Dictyostelium discoideum, has both permanent and temporary associations 

with bacteria. Here we focus on culturable bacterial associates in order to 

interrogate their relationship with D. discoideum. To do this, we isolated 

over 250 D. discoideum fruiting body samples from soil and deer feces at 

Mountain Lake Biological Station. In one-third of the wild D. discoideum we 

tested, one to six bacterial species were found per fruiting body sorus (spore 

mass) for a total of 174 bacterial isolates. The remaining two-thirds of 

D. discoideum fruiting body samples did not contain culturable bacteria, as 

is thought to be the norm. A majority (71.4%) of the unique bacterial 

haplotypes are in Proteobacteria. The rest are in either Actinobacteria, 

Bacteriodetes, or Firmicutes. The highest bacterial diversity was found in 

D. discoideum fruiting bodies originating from deer feces (27 OTUs), greater 

than either of those originating in shallow (11 OTUs) or in deep soil (4 OTUs). 

Rarefaction curves and the Chao1 estimator for species richness indicated 

the diversity in any substrate was not fully sampled, but for soil it came close. 

A majority of the D. discoideum-associated bacteria were edible by 

D. discoideum and supported its growth (75.2% for feces and 81.8% for soil 

habitats). However, we found several bacteria genera were able to evade 

phagocytosis and persist in D. discoideum cells through one or more social 

cycles. This study focuses not on the entire D. discoideum microbiome, but 

on the culturable subset of bacteria that have important eukaryote interactions 

as prey, symbionts, or pathogens. These eukaryote and bacteria interactions 

may provide fertile ground for investigations of bacteria using amoebas to gain 

an initial foothold in eukaryotes and of the origins of symbiosis and simple 

microbiomes.





submitted by:  Debra Brock [[log in to unmask]]

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[End dictyNews, volume 44, number 33]