dictyNews

Electronic Edition

Volume 49, number 24

September 29, 2023



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Abstracts

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Emerging roles for diguanylate cyclase during the evolution of 

soma in Dictyostelia



Yoshinori Kawabe1, Qingyou Du1, Takaaki B. Narita1,2 Craig Bell1,

3, Christina Schilde1,4, Koryu Kin1,5 and Pauline Schaap1*





BMC Ecology and Evolution, in press



Background: Cyclic di-guanylate (c-di-GMP), synthesized by 

diguanylate cyclase, is a major second messenger in prokaryotes, 

where it triggers biofilm formation. The dictyostelid social 

amoebas acquired diguanylate cyclase (dgcA) by horizontal gene 

transfer. Dictyostelium discoideum (Ddis) in taxon group 4 uses 

c-di-GMP as a secreted signal to induce differentiation of 

stalk cells, the ancestral somatic cell type that supports 

the propagating spores. We here investigated how this role 

for c-di-GMP evolved in Dictyostelia by exploring dgcA function 

in the group 2 species Polysphondylium pallidum (Ppal) and 

in Polysphondylium violaceum (Pvio), which resides in a small 

sister clade to group 4.

Results: Similar to Ddis, dgcA is upregulated after aggregation 

in Ppal and Pvio and predominantly expressed in the anterior 

region and stalks of emerging fruiting bodies. DgcA null mutants 

in Ppal and Pvio made fruiting bodies with very long and thin 

stalks and only few spores and showed delayed aggregation and 

larger aggregates, respectively. Ddis dgcA- cells cannot form 

stalks at all, but showed no aggregation defects. The long, thin 

stalks of Ppal and Pvio dgcA- mutants were also observed in 

acaA- mutants in these species. AcaA encodes adenylate 

cyclase A, which mediates the effects of c-di-GMP on stalk induction 

in Ddis. Other factors that promote stalk formation in Ddis are 

DIF-1, produced by the polyketide synthase StlB, low ammonia, 

facilitated by the ammonia transporter AmtC, and high oxygen, 

detected by the oxygen sensor PhyA (prolyl 4-hydroxylase). We 

deleted the single stlB, amtC and phyA genes in Pvio wild-type and 

dgcA- cells. Neither of these interventions affected stalk formation 

in Pvio wild-type and not or very mildly exacerbated the long thin 

stalk phenotype of Pvio dgcA- cells.

Conclusions: The study reveals a novel role for c-di-GMP in 

aggregation, while the reduced spore number in Pvio and Ppal dgcA- 

is likely an indirect effect, due to depletion of the cell pool by the 

extended stalk formation. The results indicate that in addition to 

c-di-GMP,  Dictyostelia ancestrally used an as yet unknown factor 

for induction of stalk formation. The activation of AcaA by c-di-GMP 

is likely conserved throughout Dictyostelia.





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

_________________________________________________________





Microfluidic single-cell measurements of oxidative stress as 

a function of cell cycle position



Tyler J Allcroft, Jessica T Duong, Per Sebastian Skardal, 

Michelle L Kovarik  





Anal Bioanal Chem, 2023 Sep 8. doi: 10.1007/s00216-023-04924-z



Single-cell measurements routinely demonstrate high levels of 

variation between cells, but fewer studies provide insight into 

the analytical and biological sources of this variation. This 

is particularly true of chemical cytometry, in which individual 

cells are lysed and their contents separated, compared to more 

established single-cell measurements of the genome and 

transcriptome. To characterize population-level variation and 

its sources, we analyzed oxidative stress levels in 1278 

individual Dictyostelium discoideum cells as a function of 

exogenous stress level and cell cycle position. Cells were 

exposed to varying levels of oxidative stress via singlet oxygen 

generation using the photosensitizer Rose Bengal. Single-cell 

data reproduced the dose–response observed in ensemble 

measurements by CE-LIF, superimposed with high levels of 

heterogeneity. Through experiments and data analysis, we 

explored possible biological sources of this heterogeneity. No 

trend was observed between population variation and oxidative 

stress level, but cell cycle position was a major contributor to 

heterogeneity in oxidative stress. Cells synchronized to the same 

stage of cell division were less heterogeneous than unsynchronized 

cells (RSD of 37–51% vs 93%), and mitotic cells had higher levels 

of reactive oxygen species than interphase cells. While past 

research has proposed changes in cell size during the cell cycle 

as a source of biological noise, the measurements presented 

here use an internal standard to normalize for effects of cell 

volume, suggesting a more complex contribution of cell cycle to 

heterogeneity of oxidative stress.





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[End dictyNews, volume 49, number 24]