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H. STRUCTURAL
BIOLOGY CENTER
H-e. Gene Network Laboratory - Emiko Suzuki
Group
RESEARCH
ACTIVITIES
(1)
Molecular and fine morphological studies on the
phototransduction in Drosophila
Emiko Suzuki
--Phototransduction
in Drosophila photoreceptor cells is a G-protein
coupled phosphoinositide (PI)-signaling cascade. It
is the most rapid process among G-protein coupled
cascade known to date (receptor potential is
generated within ~20 milliseconds after light
stimulation), and the responsiveness is dynamically
regulated. We are studying how such elaborated
signaling cascade is accomplished, from the
viewpoint of intracellular organization of the
molecules involved in this system. Our recent
studies have shown that the core components of this
cascade, phospholipase C (NORPA), protein kinase C
(INAC) and TRP channel protein, form a
macromolecular complex “transducisome" in the
photoreceptive microvilli, by binding to a scaffold
protein, INAD (collaboration with Dr. Charles
Zuker's group in U.C. San Diego). The rapidness of
phototransduction is dependent on this topological
coupling of signaling molecules. In addition to
these core components, there are several regulatory
proteins, and proteins involved in the supporting
system of phototransduciton. This year, we studied
some of these protein functions. As for the back-up
system of PI metabolism, we have found that many of
the enzymes for PI-regeneration are localized on
subrhabdomeric cisternae (SRC), the specialized
smooth endoplasmic reticulum adjacent to the
photoreceptive microvilli. Among these, we focused
on the diacylglycerol kinase 2 (RDGA) that is
essential not only for the regulation of the TRP
channel activity but also for the structural
maintenance of photoreceptors. We asked which
domain of RDGA protein molecule is important for
the intracellular targeting and/or its function. By
the expression studies of modified RDGA proteins in
photoreceptors, we found that the cysteine-rich
region of RDGA molecule is essential for the
protein localization and enzyme antivities. The
western blotting analysis showed that the RDGA
protein lacking the cysteine-rich region is
unstable. This suggests that the proper targeting
of RDGA protein is important for the protein
stability.
--Besides PI
metabolism, rhodopsin metabolism is important for
the regulation of phototransduction. This year we
studied Sunglass (SUN) protein that appears to be
involved in rhodopsin degradation. This project was
done in collaboration with Dr. Craig Montell's
Group at Johns Hopkins University School of
Medicine. We found that SUN protein co-localizes
with rhodopsin in the photoreceptor cell organelles
involved in protein degradation, and found that
sun mutant is resistant to the rhodopsin
degradation induced by bright
light1).
(2)
Fine morphological studies of the synaptic target
recognition
Emiko Suzuki
--The neuromuscular
junction of Drosophila embryonic body wall
musculature is one of the ideal models for studying
development and function of synapses at the single
cell level. Each hemisegment of an embryo/larva has
only 30 muscle cells, innervated by about 40
motoneurons. The neuromuscular projection forms in
the late embryos. During these stages, one can
fillet dissect the embryos and observe or
manipulate the development of neuromuscular
networks under a light microscope. Our previous
studies on this system using combination of single
cell labeling and electron microscopy, have
revealed the target-specific interaction of pre-
and post-synaptic cells with filopodia. This year
we studied this process by immuno-scanning electron
microscopy we have developed recently. With this
technique, we could observe the intimate
interaction of clustered muscle filopodia
(myopodia) and neuro-filopodia, that is not
recognizable by fluorescence microscopy.
(3)
Fine morphological analysis of the function of a
Ser/Thr kinase, UNC51 in Drosophila nervous
system
Hirofumi Toda*, Hiroaki
Mochizuki*, Emiko Suzuki and Katsuo
Furukubo-Tokunaga*
(*University of Tsukuba)
--UNC51 has been
known as a Ser/Thr kinase necessary for the axonal
formation in C. elegans and mice. We have
identified Drosophila gene orthologue of
unc51 in an attempt to study the detailed
molecular function of UNC51 in axonal formation by
use of Drosophila molecular genetics. We localized
the UNC51 protein to the vesicular structures in
axons and synaptic terminals by immuno-electron
microscopy. Further, we found that the unc51
gene mutation affects axonal transport of vesicular
cell organelles, by the immuofluorescence
microscopy of synaptotagmin and electron
microscopic analysis. Studies on genetic
interactions showed that UNC51 regulates axonal
elongation cooperatively with TRIO and Rac GTPases.
These results suggest that UNC51 is involved in
axonal development through interaction with the
proteins that regulate axonal membrane
trafficking.
PUBLICATIONS
Papers
1. Xu, H., Lee, S.-J., Suzuki, E., Dugan,
K.D., Stoddard, A., Li, H.-S., Chodosh, L.A. and
Montell, C. (2004). A lysosomal tetraspanin
associated with retinal degeneration identified via
a genome-wide screen. EMBO J. 23,
811-822.
2. Kohyama-Koganeya, A., Sasamura, T., Oshima, E.,
Suzuki, E., Nishihara, S., Ueda, R. and
Hirabayashi, Y. (2004). Drosophila
glucosylceramide synthase. J. Biol. Chem.
279, 35995-36002.
Review
3.
鈴木えみ子（2004）「標的認識分子から見たシナプス形成機構」細胞,36,
66-69.
ORAL
PRESENTATIONS
1.
西脇優子、小森敦子、相良洋、鈴木えみ子、岡本仁、政井一郎「視細胞外節における円盤膜形成に異常を示すゼブラフィッシュ突然変異体Twilight」第27回日本神経科学大会、大阪市、2004年9月
POSTER
PRESENTATIONS
1. Toda, H., Mochizuki, H., Suzuki, E., Hama,
C., Tomoda, T. and Furukubo-Tokunaga, K. The
conserved ser/thr kinase UNC51 functions with TRIO
& Rac to regulate neuronal development and
axonal transport in Drosophila. 4th Cold
Spring Harbor Meeting on Axon Guidance and Neural
Plasticity, Cold Spring Harbor, Sept, 2004.
2.
望月洋明、戸田浩史、鈴木えみ子、浜千尋、友田利文、古久保-徳永克男「進化的に保存されているセリン/スレオニンキナーゼであるUNC51は、神経の発生及び軸索輸送においてTrio、Racとともに協調的にはたらいている。」第27回日本神経科学大会、大阪市、2004年9月
3.
西脇優子、小森敦子、相良洋、鈴木えみ子、岡本仁、政井一郎「視細胞の分化に異常を示すゼブラフィッシュ突然変異体coronaの解析」第27回日本分子生物学会年会、神戸市、2004年12月
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