dictyNews
Electronic Edition
Volume 42, number 18
July 22, 2016

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Abstracts
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The protein domains of the Dictyostelium microprocessor that are 
required for correct subcellular localization and for microRNA 
maturation

Janis Kruse, Doreen Meier, Fides Zenk, Maren Rehders, 
Wolfgang Nellen, Christian Hammann


RNA Biology, in press

The maturation pathways of microRNAs (miRNAs) have been 
delineated for plants and several animals, belonging to the 
evolutionary supergroups of Archaeplastida and Opisthokonta, 
respectively. Recently, we reported the discovery of the 
microprocessor complex in Dictyostelium discoideum of the 
Amoebozoa supergroup. The complex is composed of the Dicer 
DrnB and the dsRBD (double-stranded RNA binding domain) 
containing protein RbdB. Both proteins localize at nucleoli, where
 they physically interact, and both are required for miRNA maturation. 
Here we show that the miRNA phenotype of a Delta-drnB gene
 deletion strain can be rescued by ectopic expression of a series 
of DrnB GFP fusion proteins, which consistently showed punctate 
perinucleolar localization in fluorescence microscopy. These 
punctate foci appear surprisingly stable, as they persist both 
disintegration of nucleoli and degradation of cellular nucleic acids. 
We observed that DrnB expression levels influence the number of 
microprocessor foci and alter RbdB accumulation. An investigation 
of DrnB variants revealed that its newly identified nuclear localization 
signal is necessary, but not sufficient for the perinucleolar localization. 
Biogenesis of miRNAs, which are RNA Pol II transcripts, is correlated 
with that localization. Besides its bidentate RNase III domains, DrnB 
contains only a dsRBD, which surprisingly is dispensable for miRNA 
maturation. This dsRBD can, however, functionally replace the 
homologous domain in RbdB. Based on the unique setup of the 
Dictyostelium microprocessor with a subcellular localization 
similar to plants, but a protein domain composition similar to 
animals, we propose a model for the evolutionary origin of 
RNase III proteins acting in miRNA maturation.


submitted by: Christian Hammann [[log in to unmask]]
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