dictyNews

Electronic Edition

Volume 46, number 26

September 18, 2020



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Abstracts

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Analysis of Barotactic and Chemotactic Guidance Cues on Directional 

Decision-making of Dictyostelium discoideum Cells in Confined 

Environments. 



Yuri Belotti, David McGloin, Cornelis J. Weijer.





PNAS, accepted



Neutrophils and dendritic cells when migrating in confined environments 

have been shown to actuate a directional choice towards paths of least 

hydraulic resistance (barotaxis), in some cases overriding chemotactic 

responses. Here, we investigate whether this barotactic response 

is conserved in the more primitive model organism Dictyostelium 

discoideum using a novel microfluidic chip design. This design allowed 

us to monitor the behavior of single cells via live imaging when 

confronted with bifurcating micro-channels, presenting different 

combinations of hydraulic and chemical stimuli. Under the conditions 

employed we find no evidence in support of a barotactic response, the 

cells base their directional choices on the chemotactic cues. When the 

cells are confronted by a microchannel bifurcation, they often split their 

leading edge and start moving into both channels, before a decision is 

made to move into one and retract from the other channel. Analysis of 

this decision-making process has shown that cells in steeper cAMP 

gradients move faster and split more readily. Furthermore, there exists 

a highly significant strong correlation between the velocity of the 

pseudopod moving up the cAMP gradient to the total velocity of the

pseudopods moving up and down the gradient over a large range of 

velocities. This suggests a role for a  critical cortical tension gradient 

in the directional decision-making proces





submitted by: Kees Weijer [[log in to unmask]]

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A Highly Conserved Iron Sulfur Cluster Assembly Machinery between

Humans and Amoeba Dictyostelium discoideum: The Characterization 

of Frataxin



Justo Olmos, Maria Florencia Pignataro, Ana Belén Benítez Dos

Santos, Mauro Bringas, Sebastián Klinke, Laura Kamenetzky, Francisco

Velazquez *, Javier Santos *





International Journal of Molecular Sciences, in press

 

Several biological activities depend on iron–sulfur clusters ([Fe-S]). 

Even though they are well-known in several organisms their function 

and metabolic pathway were poorly understood in the majority of the 

organisms. We propose to use the amoeba Dictyostelium discoideum, 

as a biological model to study the biosynthesis of [Fe-S] at the molecular, 

cellular and organism levels. First, we have explored the D. discoideum 

genome looking for genes corresponding to the subunits that constitute 

the molecular machinery for Fe-S cluster assembly and, based on the 

structure of the mammalian supercomplex and amino acid conservation 

profiles, we inferred the full functionality of the amoeba machinery. After 

that, we expressed the recombinant mature form of D. discoideum frataxin 

protein (DdFXN), the kinetic activator of this pathway. We characterized 

the protein and its conformational stability. DdFXN is monomeric and 

compact. The analysis of the secondary structure content, calculated using 

the far-UV CD spectra, was compatible with the data expected for the FXN 

fold, and near-UV CD spectra were compatible with the data corresponding 

to a folded protein. In addition, Tryptophan fluorescence indicated that the 

emission occurs from an apolar environment. However, the conformation 

of DdFXN is significantly less stable than that of the human FXN, (4.0 vs. 

9.0 kcal mol-1, respectively). Based on a sequence analysis and structural 

models of DdFXN, we investigated key residues involved in the interaction 

of DdFXN with the supercomplex and the effect of point mutations on the 

energetics of the DdFXN tertiary structure. More than 10 residues involved 

in Friedreich’s Ataxia are conserved between the human and DdFXN 

forms, and a good correlation between mutational effect on the energetics 

of both proteins were found, suggesting the existence of similar sequence/

function/stability relationships. Finally, we integrated this information in an 

evolutionary context which highlights particular variation patterns between 

amoeba and humans that may reflect a functional importance of specific 

protein positions. Moreover, the complete pathway obtained forms a piece 

of evidence in favor of the hypothesis of a shared and highly conserved 

[Fe-S] assembly machinery between Human and D. discoideum.





submitted by: Francisco Velazquez [[log in to unmask]]

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[End dictyNews, volume 46, number 26]