dictyNews
Electronic Edition
Volume 41, number 2
January 16, 2015
Please submit abstracts of your papers as soon as they have been
accepted for publication by sending them to [log in to unmask]
or by using the form at
http://dictybase.org/db/cgi-bin/dictyBase/abstract_submit.
Back issues of dictyNews, the Dicty Reference database and other
useful information is available at dictyBase - http://dictybase.org.
Follow dictyBase on twitter:
http://twitter.com/dictybase
=========
Abstracts
=========
Mechanical stress and network structure drive protein dynamics
during cytokinesis.
Vasudha Srivastava and Douglas N. Robinson
Curr. Biol. 2015, in press
Cell shape changes associated with processes like cytokinesis and
motility proceed on several second time-scales, but are derived
from molecular events, including protein-protein interactions,
assembly, and force generation by molecular motors, all of which
occur much faster [1-4]. Therefore, defining the dynamics of
such molecular machinery is critical for understanding cell shape
regulation. In addition to signaling pathways, mechanical
stresses also direct cytoskeletal protein accumulation [5-7].
A myosin II-based mechanosensory system controls cellular
contractility and shape during cytokinesis and under applied stress
[6, 8]. In Dictyostelium, this system tunes myosin II accumulation
by feedback through the actin network, particularly through the
crosslinker cortexillin I. Cortexillin-binding IQGAPs are major
regulators of this system. Here, we defined the short time-scale
dynamics of key cytoskeletal proteins during cytokinesis and under
mechanical stress using fluorescence recovery after photobleaching
and fluorescence correlation spectroscopy, to examine the dynamic
interplay between these proteins. Equatorially enriched proteins
including cortexillin I, IQGAP2, and myosin II recovered much more
slowly than actin and polar crosslinkers. The mobility of
equatorial proteins was greatly reduced at the furrow compared to
the interphase cortex, suggesting their stabilization during
cytokinesis. This mobility shift did not arise from a single
biochemical event, but rather from a global inhibition of protein
dynamics by mechanical stress-associated changes in the cytoskeletal
structure. Mechanical tuning of contractile protein dynamics
provides robustness to the cytoskeletal framework responsible for
regulating cell shape and contributes to cytokinesis fidelity.
Submitted by Doug Robinson [[log in to unmask]]
----------------------------------------------------------------------
The centrosomal component CEP161 of Dictyostelium discoideum
interacts with the Hippo signaling pathway
Salil K. Sukumaran, Rosemarie Blau-Wasser, Meino Rohlfs, Christoph
Gallinger, Michael Schleicher, Angelika A. Noegel
Cell Cycle, in press
CEP161 is a novel component of the Dictyostelium discoideum
centrosome which was identified as binding partner of the
pericentriolar component CP250. Here we show that the amino acids
1-763 of the 1381 amino acids CEP161 are sufficient for CP250
binding, centrosomal targeting and centrosome association. Analysis
of AX2 cells over-expressing truncated and full length CEP161
proteins revealed defects in growth and development. By
immunoprecipitation experiments we identified the Hippo related
kinase SvkA (Hrk-svk) as binding partner for CEP161. Both proteins
colocalize at the centrosome. In in vitro kinase assays the
N-terminal domain of CEP161 (residues 1-763) inhibited the kinase
activity of Hrk-svk. A comparison of D. discoideum Hippo kinase
mutants with mutants overexpressing CEP161 polypeptides revealed
similar defects. We propose that the centrosomal component CEP161
is a novel player in the Hippo signaling pathway and affects
various cellular properties through this interaction
Submitted by Angelika Noegel [[log in to unmask]]
----------------------------------------------------------------------
TipC and the chorea-acanthocytosis protein VPS13A regulate
autophagy in Dictyostelium and human HeLa cells
Sandra Muńoz-Braceras, Rosa Calvo and Ricardo Escalante
Autophagy, in press
Deficient autophagy causes a distinct phenotype in Dictyostelium
discoideum, characterized by the formation of multitips at the
mound stage. This led us to analyze autophagy in a number of
multitipped mutants described previously (tipA–, tipB–, tipC–,
and tipD–). We found a clear autophagic dysfunction in tipC– and
tipD– while the others showed no defects. tipD codes for a
homologue of Atg16, which confirms the role of this protein in
Dictyostelium autophagy and validates our approach. The tipC-
encoded protein is highly similar to human VPS13A (also known
as Chorein), whose mutations cause the chorea-acanthocytosis
syndrome. No member of the VPS13 protein family has been
previously related to autophagy despite the presence of a
region of similarity to Atg2 at the C-terminus. This region
also contains the conserved domain of unknown function DUF1162.
Of interest, the expression of the TipC C-terminal coding
sequence containing these two motifs largely complemented the
mutant phenotype. Dictyostelium cells lacking TipC displayed
a reduced number of autophagosomes visualized with the markers
GFP-Atg18 and GFP-Atg8 and an impaired autophagic degradation
as determined by a proteolytic cleavage assay. Downregulation
of human VPS13A in HeLa cells by RNA interference confirmed
the participation of the human protein in autophagy. VPS13A-
depleted cells showed accumulation of autophagic markers and
impaired autophagic flux.
Submitted by Ricardo Escalante [[log in to unmask]]
==============================================================
[End dictyNews, volume 41, number 2]
|
