856 research outputs found
Interpretation of the expansion law of planetary nebulae
We reproduce the expansion velocity--radius (--)
relation in planetary nebulae by considering a simple dynamical model, in order
to investigate the dynamical evolution and formation of planetary nebulae. In
our model, the planetary nebula is formed and evolving by interaction of a fast
wind from the central star with a slow wind from its progenitor, the AGB star.
In particular, taking account of the mass loss history of the AGB star makes us
succeed in the reproduction of the observed -
sequence. As a result, examining the ensemble of the observational and
theoretical evolution models of PNe, we find that if the AGB star pulsates and
its mass loss rate changes with time (from yr
to yr), the model agrees with the observations.
In terms of observation, we suggest that there are few planetary nebulae with
larger expansion velocity and smaller radius because the evolutionary
time-scale of such nebulae is so short and the size of nebulae is so compact
that it is difficult for us to observe them.Comment: 16 pages, 18 figure1, PASJ in pres
Revisiting Aire and tissue-restricted antigens at single-cell resolution
The thymus is a highly specialized organ that plays an indispensable role in the establishment of self-tolerance, a process characterized by the “education” of developing T-cells. To provide competent T-cells tolerant to self-antigens, medullary thymic epithelial cells (mTECs) orchestrate negative selection by ectopically expressing a wide range of genes, including various tissue-restricted antigens (TRAs). Notably, recent advancements in the high-throughput single-cell analysis have revealed remarkable heterogeneity in mTECs, giving us important clues for dissecting the mechanisms underlying TRA expression. We overview how recent single-cell studies have furthered our understanding of mTECs, with a focus on the role of Aire in inducing mTEC heterogeneity to encompass TRAs
Aire suppresses CTLA-4 expression from the thymic stroma to control autoimmunity
Impaired production of thymic regulatory T cells (Tregs) is implicated in the development of Aire-dependent autoimmunity. Because Tregs require agonistic T cell receptor stimuli by self-antigens to develop, reduced expression of self-antigens from medullary thymic epithelial cells (mTECs) has been considered to play a major role in the reduced Treg production in Aire deficiency. Here, we show that mTECs abnormally express co-inhibitory receptor CTLA-4 if Aire is non-functional. Upon binding with CD80/CD86 ligands expressed on thymic dendritic cells (DCs), the ectopically expressed CTLA-4 from Aire-deficient mTECs removes the CD80/CD86 ligands from the DCs. This attenuates the ability of DCs to provide co-stimulatory signals and to present self-antigens transferred from mTECs, both of which are required for Treg production. Accordingly, impaired production of Tregs and organ-specific autoimmunity in Aire-deficient mice are rescued by the depletion of CTLA-4 expression from mTECs. Our studies illuminate the significance of mTEC-DC interaction coordinated by Aire for the establishment of thymic tolerance
Tropical Support Vector Machines: Evaluations and Extension to Function Spaces
Support Vector Machines (SVMs) are one of the most popular supervised
learning models to classify using a hyperplane in an Euclidean space. Similar
to SVMs, tropical SVMs classify data points using a tropical hyperplane under
the tropical metric with the max-plus algebra. In this paper, first we show
generalization error bounds of tropical SVMs over the tropical projective
space. While the generalization error bounds attained via VC dimensions in a
distribution-free manner still depend on the dimension, we also show
theoretically by extreme value statistics that the tropical SVMs for
classifying data points from two Gaussian distributions as well as empirical
data sets of different neuron types are fairly robust against the curse of
dimensionality. Extreme value statistics also underlie the anomalous scaling
behaviors of the tropical distance between random vectors with additional noise
dimensions. Finally, we define tropical SVMs over a function space with the
tropical metric and discuss the Gaussian function space as an example
Nonacyclic Ladder Silsesquioxanes and Spectral Features of Ladder Polysilsesquioxanes
Laddersiloxanes, that is, ladder silsesquioxanes with defined structures, could be obtained by stepwise synthesis starting from cyclic silanols. These compounds were shown to have high thermal stability. As an extension of the previous work, the first nonacyclic ladder silsesquioxanes were synthesized by the reaction of bicyclic silanol with tricyclic tetrachloride, which were obtained from cyclic silanols. The structure was confirmed by spectral measurements, and the spectral features of a series of ladder polysilsesquioxanes with determined structures were analyzed
Decay Profiles and Spectra of Stimulated Luminescence in CdI2
Decay profiles and spectral distributions of the stimulated luminescence in Cdl2 crystals
have been investigated at liquid nitrogen temperature under high density excitation
with a N2-gas laser in the excitonic absorption band. The observed luminescence decay
curve consists of two components, fast (< 20 ns) and slow (about 5 μs) ones. The slow
component is identical to the main decay component of the spontaneous emission which
is observed rather strongly in the case of low density excitation. The fast component
is peculiar to the case of high density excitation, and is connected to the stimulated
emission. This means that the stimulated luminescence appears in the early stage of
the luminescence decay. The spectral distribution of the fast component, namely, the
stimulated emission spectrum, consists of eight fine-structures and is different from the
usual spontaneous emission spectum from self trapped exciton (STE) states. Discussions
will be made on the origin of these structures relating it with fine-structures of the STE
states
Revisiting Aire and tissue-restricted antigens at single-cell resolution
The thymus is a highly specialized organ that plays an indispensable role in the establishment of self-tolerance, a process characterized by the “education” of developing T-cells. To provide competent T-cells tolerant to self-antigens, medullary thymic epithelial cells (mTECs) orchestrate negative selection by ectopically expressing a wide range of genes, including various tissue-restricted antigens (TRAs). Notably, recent advancements in the high-throughput single-cell analysis have revealed remarkable heterogeneity in mTECs, giving us important clues for dissecting the mechanisms underlying TRA expression. We overview how recent single-cell studies have furthered our understanding of mTECs, with a focus on the role of Aire in inducing mTEC heterogeneity to encompass TRAs
A NEW LOOK AT TRANSCRIPTIONAL REGULATION BY AIRE IN mTECs
The deficiency of Aire, a transcriptional regulator whose defect results in the development of autoimmunity, is associated with reduced expression of tissue-restricted self-Ags (TRAs) in medullary thymic epithelial cells (mTECs). Although the mechanisms underlying Aire-dependent expression of TRAs need to be explored, the physical identification of the target(s) of Aire has been hampered by the low and promiscuous expression of TRAs. We have tackled this issue by engineering mice with augmented Aire expression. Integration of the transcriptomic data from Aire-augmented and Aire-deficient mTECs revealed that a large proportion of so-called Aire-dependent genes, including those of TRAs, may not be direct transcriptional targets downstream of Aire. Rather, Aire induces TRA expression indirectly through controlling the heterogeneity of mTECs, as revealed by single-cell analyses. In contrast, Ccl25 emerged as a canonical target of Aire, and we verified this both in vitro and in vivo. Our approach has illuminated the Aire’s primary targets while distinguishing them from the secondary targets
Neural RNA-binding protein Musashi1 inhibits translation initiation by competing with eIF4G for PABP
Musashi1 (Msi1) is an RNA-binding protein that is highly expressed in neural stem cells. We previously reported that Msi1 contributes to the maintenance of the immature state and self-renewal activity of neural stem cells through translational repression of m-Numb. However, its translation repression mechanism has remained unclear. Here, we identify poly(A) binding protein (PABP) as an Msi1-binding protein, and find Msi1 competes with eIF4G for PABP binding. This competition inhibits translation initiation of Msi1's target mRNA. Indeed, deletion of the PABP-interacting domain in Msi1 abolishes its function. We demonstrate that Msi1 inhibits the assembly of the 80S, but not the 48S, ribosome complex. Consistent with these conclusions, Msi1 colocalizes with PABP and is recruited into stress granules, which contain the stalled preinitiation complex. However, Msi1 with mutations in two RNA recognition motifs fails to accumulate into stress granules. These results provide insight into the mechanism by which sequence-specific translational repression occurs in stem cells through the control of translation initiation
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