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Electronic Edition

Volume 45, number 15

June 21, 2019



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Abstracts

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A telomerase with novel non-canonical roles: TERT controls cellular 

aggregation and tissue size in Dictyostelium. 



Nasna Nassir, Geoff Hyde, Ramamurthy Baskar 



Department of Biotechnology, Indian Institute of Technology-Madras, 

Chennai-600036, India. 





PLoS Genet 15(6): e1008188.



Telomerase, particularly its main subunit, the reverse transcriptase, 

TERT, prevents DNA erosion during eukaryotic chromosomal replication, 

but also has poorly understood noncanonical functions. Here, in the 

model social amoeba Dictyostelium discoideum, we show that the protein 

encoded by tert has telomerase-like motifs, and regulates, non-canonically, 

important developmental processes. Expression levels of wild-type (WT) 

tert were biphasic, peaking at 8 and 12 h post-starvation, aligning with 

developmental events, such as the initiation of streaming (~7 h) and mound 

formation (~10 h). In tert KO mutants, however, aggregation was delayed 

until 16 h. Large, irregular streams formed, then broke up, forming small 

mounds. The mound-size defect was not induced when a KO mutant of 

countin (a master size-regulating gene) was treated with TERT inhibitors, 

but anti-countin antibodies did rescue size in the tert KO. Although, 

conditioned medium (CM) from countin mutants failed to rescue size in the 

tert KO, tert KO CM rescued the countin KO phenotype. These and additional 

observations indicate that TERT acts upstream of smlA/countin: (i) the 

observed expression levels of smlA and countin, being respectively lower 

and higher (than WT) in the tert KO; (ii) the levels of known size-regulation 

intermediates, glucose (low) and adenosine (high), in the tert mutant, and the 

size defect’s rescue by supplemented glucose or the adenosine-antagonist, 

caffeine; (iii) the induction of the size defect in the WT by tert KO CM and 

TERT inhibitors. The tert KO’s other defects (delayed aggregation, irregular 

streaming) were associated with changes to cAMP-regulated processes (e.g. 

chemotaxis, cAMP pulsing) and their regulatory factors (e.g. cAMP; acaA, 

carA expression). Overexpression of WT tert in the tert KO rescued these 

defects (and size), and restored a single cAMP signaling centre. Our results 

indicate that TERT acts in novel, non-canonical and upstream ways, 

regulating key developmental events in Dictyostelium.





submitted by:  Ramamurthy Baskar  [[log in to unmask]]

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The Architecture of Traveling Actin Waves Revealed by Cyroelectron 

Tomography, 



Marion Jasnin, Florian Beck, Mary Ecke, Yoshiyuki Fukuda, Antonio Martinez-

Sanchez, Wolfgang Baumeister, and Günther Gerisch. 





Structure, https://doi.org/10.1016/j.str.2019.05.009, in press 



Actin waves are dynamic supramolecular structures involved in cell migration, 

cytokinesis, adhesion, and neurogenesis. Although wave-like propagation of 

actin networks is a widespread phenomenon, the actin architecture underlying 

wave propagation remained unknown. In situ cryoelectron tomography of 

Dictyostelium cells unveils the wave architecture and provides evidence for 

wave progression by de novo actin nucleation. Subtomogram averaging 

reveals the structure of Arp2/3 complex-mediated branch junctions in their 

native state, and enables quantitative analysis of the three-dimensional 

organization of branching within the waves. We find an excess of branches 

directed toward the substrate-attached membrane, and tent-like structures at 

sites of branch clustering. Fluorescence imaging shows that Arp2/3 clusters 

follow accumulation of the elongation factor VASP. We propose that filament 

growth toward the membrane lifts up the actin network as the wave propagates, 

until depolymerization of oblique filaments at the back causes the collapse of 

horizontal filaments into a compact layer.





submitted by:  Günther Gerisch  [[log in to unmask]]

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[End dictyNews, volume 45, number 15]