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dictyNews Volume 38 Number 17
dictyNews
Electronic Edition
Volume 38, number 17
July 6, 2012
Please submit abstracts of your papers as soon as they have been
accepted for publication by sending them to dicty@northwestern.edu
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
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Abstracts
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'A Retinoblastoma Orthologue is a Major Regulator of S-phase, Mitotic,
and Developmental Gene Expression in Dictyostelium'
Kimchi Strasser1, Gareth Bloomfield2, Asa MacWilliams3,
Adriano Ceccarelli4, Harry MacWilliams5, Adrian Tsang1
1 Biology Department and Centre for Structural and Functional Genomics,
Concordia University, Montreal, QC, Canada
2 MRC Laboratory of Molecular Biology, Cambridge, UK and
Wellcome Trust Sanger Institute, Hinxton, UK
3 Siemens Corporate Technology, Munich, Germany
4 Neuroscience Institute Cavalieri Ottolenghi, University of Torino, Italy
5 Biozentrum der Ludwig-Maximilans-Universitt, Munich, Germany
PLoS ONE, in press
The retinoblastoma tumour suppressor, Rb, has two major functions.
First, it represses genes whose products are required for S-phase entry
and progression thus stabilizing cells in G1. Second, Rb interacts with
factors that induce cell-cycle exit and terminal differentiation.
Dictyostelium lacks a G1 phase in its cell cycle but it has a retinoblastoma
orthologue, rblA.
Using microarray analysis and mRNA-Seq transcriptional profiling, we
show that RblA strongly represses genes whose products are involved in
S phase and mitosis. Both S-phase and mitotic genes are upregulated at
a single point in late G2 and again in mid-development, near the time
when cell cycling is reactivated. RblA also activates a set of genes unique
to slime moulds that function in terminal differentiation.
Like its mammalian counterpart Dictyostelium RblA plays a dual role,
regulating cell-cycle progression and transcriptional events leading to
terminal differentiation. In the absence of a G1 phase, however, RblA
functions in late G2 controlling the expression of both S-phase and
mitotic genes.
Submitted by Kimchi Strasser [kimchi@gene.concordia.ca]
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Conservation and divergence between cytoplasmic and muscle-specific
actin capping proteins: insights from the crystal structure of cytoplasmic
Cap32/34 from Dictyostelium discoideum.
Eckert C, Goretzki A, Faberova M, Kollmar M.
BMC Struct Biol. 2012 Jun 1;12(1):12. [Epub ahead of print]
http://www.biomedcentral.com/1472-6807/12/12/abstract
BACKGROUND:
Capping protein (CP), also known as CapZ in muscle cells and Cap32/34
in Dictyostelium discoideum, plays a major role in regulating actin filament
dynamics. CP is a ubiquitously expressed heterodimer comprising an alpha-
and beta-subunit. It tightly binds to the fast growing end of actin filaments,
thereby functioning as a "cap" by blocking the addition and loss of actin
subunits. Vertebrates contain two somatic variants of CP, one being
primarily found at the cell periphery of non-muscle tissues while the
other is mainly localized at the Z-discs of skeletal muscles.
RESULTS:
To elucidate structural and functional differences between cytoplasmic
and sarcomercic CP variants, we have solved the atomic structure of
Cap32/34 (32 = beta- and 34 = alpha-subunit) from the cellular slime
mold Dictyostelium at 2.2 A resolution and compared it to that of chicken
muscle CapZ. The two homologs display a similar overall arrangement
including the attached alpha-subunit C-terminus (alpha-tentacle) and
the flexible beta-tentacle. Nevertheless, the structures exhibit marked
differences suggesting considerable structural flexibility within the
alpha-subunit. In the alpha-subunit we observed a bending motion of
the beta-sheet region located opposite to the position of the C-terminal
beta-tentacle towards the antiparallel helices that interconnect the
heterodimer. Recently, a two domain twisting attributed mainly to the
beta-subunit has been reported. At the hinge of these two domains
Cap32/34 contains an elongated and highly flexible loop, which has
been reported to be important for the interaction of cytoplasmic CP
with actin and might contribute to the more dynamic actin-binding of
cytoplasmic compared to sarcomeric CP (CapZ).
CONCLUSIONS:
The structure of Cap32/34 from Dictyostelium discoideum allowed
a detailed analysis and comparison between the cytoplasmic and
sarcomeric variants of CP. Significant structural flexibility could
particularly be found within the alpha-subunit, a loop region in the
beta-subunit, and the surface of the alpha-globule where the amino
acid differences between the cytoplasmic and sarcomeric mammalian
CP are located. Hence, the crystal structure of Cap32/34 raises the
possibility of different binding behaviours of the CP variants toward the
barbed end of actin filaments, a feature, which might have arisen from
adaptation to different environments.
Submitted by Martin Kollmar [mako@nmr.mpibpc.mpg.de]
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[End dictyNews, volume 38, number 17]
