dictyNews

Electronic Edition

Volume 49, number 3

January 27, 2023



Please submit abstracts of your papers as soon as they have been

accepted for publication by sending them to [log in to unmask]

or by using the form at

http://dictybase.org/db/cgi-bin/dictyBase/abstract_submit.



Back issues of dictyNews, the Dicty Reference database and other

useful information is available at dictyBase - http://dictybase.org.



Follow dictyBase on twitter:

http://twitter.com/dictybase





=========

Abstracts

=========





Autophagy of the somatic stalk cells likely nurses the propagating 

spores of Dictyostelid social amoebas  

  

Qingyou Du and Pauline Schaap 

 

School of Life Sciences, University of Dundee, Dundee, Angus, 

DD15EH, UK 

              



Open Research Europe, in press



Background:  Autophagy (self-feeding) assists survival of starving 

cells by partial self-digestion, while dormancy as cysts, spores 

or seeds enables long-term survival. Starving Dictyostelium 

amoebas construct multicellular fruiting bodies with spores and 

stalk cells, with many Dictyostelia still able to encyst individually 

like their single-celled ancestors. While autophagy mostly occurs 

in the somatic stalk cells, autophagy gene knock-outs in 

Dictyostelium discoideum (D. discoideum) formed no spores and 

lacked cAMP induction of prespore gene expression. 

Methods: To investigate whether autophagy also prevents 

encystation, we knocked-out autophagy genes atg5 and atg7 in 

the dictyostelid Polysphondylium pallidum, which forms both spores 

and cysts. We measured spore and cyst differentiation and viability 

in the knock-out as well as stalk and spore gene expression and its 

regulation by cAMP. We tested a hypothesis that spores require 

materials derived from autophagy in stalk cells. Sporulation 

requires secreted cAMP acting on receptors and intracellular cAMP 

acting on PKA. We compared the morphology and viability of spores 

developed in fruiting bodies with spores induced from single cells 

by stimulation with cAMP and 8Br-cAMP, a membrane-permeant 

PKA agonist. 

Results: Loss of autophagy in P. pallidum reduced but did not 

prevent encystation. Stalk cells still differentiated but stalks 

were disorganised. However, no spores were formed at all , 

but not stalk differentiation, and cAMP-induced prespore gene 

expression was lost. D. discoideum spores induced in vitro by 

cAMP and 8Br-cAMP were smaller and rounder than spores 

formed multicellularly and while they were not lysed by detergent 

they germinated not (strain Ax2) or poorly (strain NC4), unlike 

multicellular spores formed in fruiting bodies. 

Conclusions: The stringent requirement of sporulation on both 

multicellularity and autophagy, which occurs mostly in stalk cells, 

suggests that stalk cells nurse the spores through autophagy. 

This highlights autophagy as a major cause for somatic cell 

evolution in early multicellularity. 





Submitted by Pauline Schaap [[log in to unmask]]

_________________________________________________________





Development of the dictyostelid Polysphondylium violaceum  does 

not require secreted cAMP 

 

Yoshinori Kawabe and Pauline Schaap 

School of Life Sciences, University of Dundee, Dundee DD15EH, UK 

 



Biology Open, in press

 

Group 4 Dictyostelia, like D. discoideum, self-organize into 

aggregates and fruiting bodies using propagating waves of the 

chemoattractant cAMP, which are produced by a network containing 

the adenylate cyclase AcaA, cAMP receptors (Cars) and the 

extracellular cAMP phosphodiesterase PdsA. Additionally, AcaA and 

the adenylate cyclases AcrA and AcgA produce secreted cAMP for 

induction of aggregative and prespore gene expression and 

intracellular cAMP for PKA activation, with PKA triggering initiation 

of development and spore and stalk maturation. Non-group 4 

species also use secreted cAMP to coordinate post-agggregative 

morphogenesis and prespore induction, but use other attractants to 

aggregate. To understand how cAMP's role in aggregation evolved, 

we deleted the acaA, carA and pdsA genes of Polysphondylium 

violaceum, a sister species to group 4. acaAˉ fruiting bodies had 

thinner stalks but otherwise developed normally. Deletion of acrA, 

which was similarly expressed as acaA, reduced aggregation centre 

initiation and, as also occurred after D. discoideum acrA deletion, 

caused spore instability. Double acaAˉacrAˉ mutants failed to form 

stable aggregates, a defect that was overcome by exposure to the 

PKA agonist 8Br-cAMP, and therefore likely due to reduced 

intracellular cAMP. The carAˉ and pdsAˉ mutants showed normal 

aggregation and fruiting body development. Together, the data 

showed that P. violaceum development does not critically require 

secreted cAMP, while roles of intracellular cAMP in initiation of 

development and spore maturation are conserved. Apparently, 

cell-cell communication underwent major taxon-group specific 

innovation in Dictyostelia.  





Submitted by Pauline Schaap [[log in to unmask]]

========================================================

[End dictyNews, volume 49, number 3]