dictyNews
Electronic Edition
Volume 48, number 20
October 7, 2022

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Abstracts
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EAdenylate cyclase A amplification and functional diversification 
during Polyspondylium pallidum development

Yoshinori Kawabe and Pauline Schaap

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


EvoDevo,, in press

Background: In Dictyostelium discoideum (Ddis) adenylate cyclase A 
(ACA) critically generates the cAMP oscillations that coordinate 
aggregation and morphogenesis. Unlike group 4 species like Ddis, 
other groups do not use extracellular cAMP to aggregate. However, 
deletion of cAMP receptors (cARs) or extracellular phosphodiesterase 
(PdsA) in Polyspondylium pallidum (Ppal, group 2) blocks fruiting 
body formation, suggesting that cAMP oscillations ancestrally 
control post-aggregative morphogenesis. In group 2, the acaA gene 
underwent several duplications. We deleted the three Ppal aca genes 
to identify roles for either gene and tested whether Ppal shows 
transient cAMP-induced cAMP accumulation, which underpins 
oscillatory cAMP signalling. 

Results: In contrast to Ddis, pre-aggregative Ppal cells did not 
produce a pulse of cAMP upon stimulation with the cAR agonist 
2'H-cAMP, but acquired this ability after aggregation. Deletion of 
Ppal aca1, aca2 and aca3 yielded different phenotypes. aca1- cells 
showed relatively thin stalks, aca2- showed delayed secondary sorogen 
formation and aca3- formed less aggregation centers. The aca1-/aca2- 
and aca1-/aca3- mutants combined individual defects, while aca2-/aca3- 
and aca1-aca3-aca2- additionally showed >24 h delay in aggregation, 
with only few aggregates with fragmenting streams being formed. The 
fragments developed into small fruiting bodies with stalk and spore 
cells. Aggregation was restored in aca2-/aca3- and aca1-/aca3/aca2-
by 2.5 mM 8Br-cAMP, a membrane-permeant activator of cAMP-dependent 
protein kinase (PKA). Like Ddis, Ppal sorogens also express the 
adenylate cyclases ACR and ACG. We found that prior to aggregation, 
Ddis aca-/ACG cells produced a pulse of cAMP upon stimulation with 
2'H-cAMP, indicating that cAMP oscillations may not be dependent on 
ACA alone.

Conclusions: The three Ppal replicates of acaA perform different roles 
in stalk morphogenesis, secondary branch formation and aggregation in 
Ppal, but act together to enable development by activating PKA. While 
even an aca1-/aca3-/aca2- mutant still forms (some) fruiting bodies, 
suggesting little need for ACA-induced cAMP oscillations in this 
process, we found that ACG also mediated transient cAMP-induced cAMP 
accumulation. It therefore remains likely that post-aggregative Ppal 
morphogenesis is organized by cAMP oscillations, favouring a previously 
proposed model where cAR-regulated cAMP hydrolysis rather than its 
synthesis dominates oscillatory behaviour.


Submitted by Pauline Schaap [[log in to unmask]]
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[End dictyNews, volume 48, number 20]