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Homma Kosuke Akashi Nobuhiro Abe Tomoyuki Hasegawa Mikio Harada Kenichi Hirabuki Yoshihiko Irie Kiyoshi Kaji Mikio Miguchi Hideo Mizoguchi Noriyasu Mizunaga Hiromi Nakashizuka Tohru Natume Syunji Niiyama Kaoru Ohkubo Tatsuhiro Sawada Shin-ichi Sugita Hisashi Takatsuki Seiki Yamanaka Norikazu 《Plant Ecology》1999,140(2):129-138
The causes and timing of seed death in early regeneration process of Siebold's beech (Fagus crenata Blume) was studied at 15 sites along a snowfall gradient in Japan, in order to clarify why the seedling density of the species has geographic difference remarkably. Seed production did not significantly differ along the snowfall gradient. Pre-dispersal seed mortality by insect damage was higher at sites with light snowfall than at sites with heavy snowfall, but this only seemed to be a minor factor influencing the population. A large proportion of the viable nuts that fall in autumn ware killed in winter before germination. Winter mortality was much higher at sites with thin snow cover than that at sites with thick snow cover, and this factor was strongly correlated with the geographic variation of seedling regeneration probability. There was little seed mortality by winter desiccation. The main factor contributing to the geographic difference seemed to be a seed predation by rodents in winter. Deep snow cover may reduce the success of rodents finding seeds in winter. Thus the observed relationship between snowpack depth and early mortality may be due to an indirect effect through the process of seed predation.p> 相似文献
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Shotaro Saita Michiko Shirane Tohru Natume Shun-ichiro Iemura Keiichi I. Nakayama 《The Journal of biological chemistry》2009,284(20):13766-13777
Protrudin is a protein that contains a Rab11-binding domain and a FYVE
(lipid-binding) domain and that functions to promote neurite formation through
interaction with the GDP-bound form of Rab11. Protrudin also contains a short
sequence motif designated FFAT (two phenylalanines in an acidic tract), which
in other proteins has been shown to mediate binding to vesicle-associated
membrane protein-associated protein (VAP). We now show that protrudin
associates and colocalizes with VAP-A, an isoform of VAP expressed in the
endoplasmic reticulum. Both the interaction between protrudin and VAP-A as
well as the induction of process formation by protrudin were markedly
inhibited by mutation of the FFAT motif. Furthermore, depletion of VAP-A by
RNA interference resulted in mislocalization of protrudin as well as in
inhibition of neurite outgrowth induced by nerve growth factor in rat
pheochromocytoma PC12 cells. These defects resulting from depletion of
endogenous rat VAP-A in PC12 cells were corrected by forced expression of (RNA
interference-resistant) human VAP-A but not by VAP-A mutants that have lost
the ability to interact with protrudin. These results suggest that VAP-A is an
important regulator both of the subcellular localization of protrudin and of
its ability to stimulate neurite outgrowth.The molecular mechanisms that underlie neurite formation include both
cytoskeletal remodeling and membrane trafficking. Membrane components are
transported in a directional manner within the cell by a membrane recycling
system, resulting in expansion of the surface area of the neurite. The small
GTPase Rab11 regulates membrane recycling and constitutive exocytosis
(1), and it is thought to
contribute to neurite formation through regulation of directional membrane
transport.We have recently identified protrudin as a key regulator of Rab11-dependent
membrane trafficking during neurite extension. Protrudin interacts with FKBP38
(also known as FKBP8) (2),
which is a member of the immunophilin family of proteins that bind the
immunosuppressant drug FK506
(3). FKBPs are multifunctional
proteins that regulate the folding or export of other proteins as a result of
their peptidyl-prolyl cis-trans-isomerase activity
(4). Protrudin was found to
interact with FKBP38, but not with other FKBP proteins such as FKBP12 or
FKBP52 (5). Protrudin is
hyperphosphorylated in Fkbp38-/- mice, which manifest
abnormal extension of nerve fibers
(5).Protrudin contains a Rab11-binding domain (RBD11), two transmembrane
domains (TM1 and
TM2),2 an FFAT (two
phenylalanines in an acidic tract) motif
(6), a coiled-coil domain, and
a FYVE domain (7). These
structural characteristics suggested that protrudin might function in membrane
trafficking, particularly in membrane recycling. The gene encoding ZFYVE27 (a
synonym of human protrudin) was recently found to be mutated in a German
family with an autosomal dominant form of hereditary spastic paraplegia
(AD-HSP), which is characterized by selective degeneration of axons
(8). The phenotype of the
affected individuals is similar to that of patients with AD-HSP caused by
mutation of spastin, a protein implicated in neuronal vesicular trafficking
(9), and protrudin was shown to
interact with spastin (8).
These findings support the notion that protrudin plays a key role in
Rab11-mediated directional membrane transport during neurite formation.The subcellular localization of protrudin is dynamic. Whereas it is
localized to the endoplasmic reticulum (ER) under basal conditions, nerve
growth factor (NGF) triggers the translocation of protrudin from the ER, via
recycling endosomes, to the tip of membrane protrusions in neuronal cells.
Given that the FFAT motif is thought to serve as an ER targeting signal
(6), this motif might be
expected to contribute both to the localization of protrudin to the ER and to
the regulation of neurite formation by this protein. The FFAT motif (consensus
amino acid sequence of EFFDAXE, where X is any amino acid)
is present in several lipid-binding proteins that are implicated in the
transfer of lipids between the ER and other organelles such as the Golgi
apparatus (10,
11). Vesicle-associated
membrane protein-associated protein (VAP) interacts with these lipid-binding
proteins through their FFAT motifs
(6,
11,
12). The VAP-A and VAP-B
isoforms of mammalian VAP are ER-resident type II membrane proteins
(13) that are encoded by
different genes (14); VAP-C is
a splicing variant of VAP-B that lacks the membrane-spanning domain. VAP-A and
VAP-B share ∼60% amino acid sequence identity, form homo- or heterodimers,
and are expressed in many tissues
(14-16).
In addition to their localization to the ER
(16), VAP-A and VAP-B are
present in a wide range of intracellular membranes or membrane structures,
including the Golgi, the ER-Golgi intermediate compartment
(17), tight junctions
(18), neuromuscular junctions
(19), recycling endosomes, and
the plasma membrane (20).We have now identified VAP-A and VAP-B as proteins that interact with
protrudin. Protrudin preferentially interacts with VAP-A via its FFAT motif,
and this motif was found to be required for the protrudin-dependent formation
of membrane protrusions in HeLa cells. In addition, depletion of VAP-A by RNA
interference resulted in inhibition of NGF-induced neurite outgrowth in the
PC12 rat pheochromocytoma cell line. This inhibition of neurite outgrowth was
reversed by expression of human VAP-A but not by that of VAP-A mutants that
have lost the ability to bind to protrudin. These results suggest that
interaction of protrudin with VAP-A is important both for its ER retention and
for its ability to stimulate neurite formation. 相似文献
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