dictyNews

Electronic Edition

Volume 43, number 1

January 13, 2017



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Abstracts

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Early nucleolar disorganization in Dictyostelium cell death 



MF Luciani, Y Song, A Sahrane, A Kosta, P Golstein





Cell Death and Disease, in press



Cell death occurs in all eukaryotes, but it is still not known 

whether some core steps of the cell death process are conserved. 

We investigated this using the protist Dictyostelium. The dissection 

of events in Dictyostelium vacuolar developmental cell death was 

facilitated by the sequential requirement for two distinct exogenous 

signals. An initial exogenous signal (starvation and cAMP) recruited 

most cells into clumps. Only within these clumps did subsequent 

cell death events take place. Contrary to our expectations, already 

this initial signal provoked nucleolar disorganization and irreversible 

inhibition of rRNA and DNA synthesis, reflecting marked cell 

dysfunction. The initial signal also primed clumped cells to respond 

to a second exogenous signal (DIF-1 or c-di-GMP), which led to 

vacuolization and synthesis of cellulose encasings. Thus, the latter 

prominent hallmarks of developmental cell death were induced 

separately from initial cell dysfunction. We propose that (1) in 

Dictyostelium vacuolization and cellulose encasings are late, 

organism-specific, hallmarks, and (2) on the basis of our observations 

in this protist and of similar previous observations in some cases of 

mammalian cell death, early inhibition of rRNA synthesis and nucleolar 

disorganization may be conserved in some eukaryotes to usher in 

developmental cell death. 





submitted by: Pierre Golstein [[log in to unmask]]

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CP39, CP75 and CP91 are major structural components of the 

Dictyostelium centrosome's core structure



Irene Meyer, Tatjana Peter, Petros Batsios, Oliver Kuhnert, 

Anne Krüger-Genge, Carl Camurça, Ralph Gräf



University of Potsdam





Eur. J. Cell Biol., in press



The acentriolar Dictyostelium centrosome is a nucleus-associated 

body consisting of a core structure with three plaque-like layers, 

which are surrounded by a microtubule-nucleating corona. The core 

duplicates once per cell cycle at the G2/M transition, whereby its 

central layer disappears and the two outer layers form the mitotic 

spindle poles. Through proteomic analysis of isolated centrosomes 

we have identified CP39 and CP75, two essential components of the 

core structure. Both proteins can be assigned to the central core 

layer as their centrosomal presence is correlated to the disappearance 

and reappearance of the central core layer in the course of centrosome 

duplication. Both proteins contain centrosomal targeting domains in 

their N- and C-terminal halves whereby the N-terminal half is required 

for cell cycle-dependent regulation. CP39 is capable of self-interaction 

and overexpression of GFP- CP39 elicits supernumerary microtubule-

organizing centers and precentrosomal cytosolic clusters. 

Underexpression stops cell growth and reverses the MTOC amplification 

phenotype. Depletion of CP75 by RNAi also elicits supernumerary 

MTOCs. In addition CP75RNAi affects correct chromosome segregation 

and causes co-depletion of CP39 and CP91, another central core layer 

component. CP39 and CP75 interact with each other directly in a yeast 

two hybrid assay. Furthermore CP39, CP75 and CP91 mutually interact 

in a proximity-dependent biotin identification (BioID) assay. Our data 

indicate that these three proteins are all required for proper centrosome 

biogenesis and make up the major structural components of core 

structure's central layer.





submitted by: Ralf Gräf  [[log in to unmask]]

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[End dictyNews, volume 43, number 31]