693 research outputs found
Tenascin-C and mechanotransduction in the development and diseases of cardiovascular system
Living tissue is composed of cells and extracellular matrix (ECM). In the heart and blood vessels, which are constantly subjected to mechanical stress, ECM molecules form well-developed fibrous frameworks to maintain tissue structure. ECM is also important for biological signaling, which influences various cellular functions in embryonic development, and physiological/pathological responses to extrinsic stimuli. Among ECM molecules, increased attention has been focused on matricellular proteins. Matricellular proteins are a growing group of non-structural ECM proteins highly up-regulated at active tissue remodeling, serving as biological mediators. Tenascin-C (TNC) is a typical matricellular protein, which is highly expressed during embryonic development, wound healing, inflammation, and cancer invasion. The expression is tightly regulated, dependent on the microenvironment, including various growth factors, cytokines, and mechanical stress. In the heart, TNC appears in a spatiotemporal-restricted manner during early stages of development, sparsely detected in normal adults, but transiently re-expressed at restricted sites associated with tissue injury and inflammation. Similarly, in the vascular system, TNC is strongly up-regulated during embryonic development and under pathological conditions with an increase in hemodynamic stress. Despite its intriguing expression pattern, cardiovascular system develops normally in TNC knockout mice. However, deletion of TNC causes acute aortic dissection (AAD) under strong mechanical and humoral stress. Accumulating reports suggest that TNC may modulate the inflammatory response and contribute to elasticity of the tissue, so that it may protect cardiovascular tissue from destructive stress responses. TNC may be a key molecule to control cellular activity during development, adaptation, or pathological tissue remodeling
Isolation of a transcriptionally active element of high copy number retrotransposons in sweetpotato genome
Many plant retrotransposons have been characterized, but only three families (Tnt1, Tto1 and
Tos17) have been demonstrated to be transpositionally competent. We followed a novel approach
that enabled us to identify an active element of the Ty1-copia retrotransposon family with
estimated 400 copies in the sweetpotato genome. DNA sequences of Ty1 -copia reverse
transcriptase (RTase) from the sweetpotato genome were analyzed, and a group of
retrotransposon copies probably formed by recent transposition events was further analyzed.
3’RACE on callus cDNA amplified transcripts containing long terminal repeats (LTR) of this
group. The sequence -specific amplification polymorphism (S-SAP) patterns of the LTR sequence
in the genomic DNA were compared between a normal plant and callus lines derived from it. A
callus -specific S-SAP product was found into which the retrotransposon detected by the 3’RACE
had been transposed apparently during cell culture. We conclude that our approach provides an
effective way to identify active elements of retrotransposons with high copy numbers.</p
Identification of the key stages for sex determination in the silkworm, Bombyx mori
In general, the master switch gene for sex determination is expressed for a limited period during the early embryonic stage. To increase our understanding of the sex determination mechanism in Bombyx mori, it is important to understand when sex determination takes place. To examine the key stages for sex determination in this insect, we focused on the expression patterns of Bmdsx (a double-switch gene in the sex determination cascade of B. mori) and BmIMP (a gene expressed specifically in males involved in male-specific splicing of Bmdsx). Reverse transcription PCR (RT-PCR) analysis revealed that male-type Bmdsx expression was observed in females at 27 and 29 h after oviposition (hao), and finally disappeared at 32 hao. Moreover, BmIMP mRNA was also expressed in these females, and its expression level was comparable to that of the male-type Bmdsx mRNA. These results demonstrated that female embryos before 32 hao can show male-type expression of Bmdsx and BmIMP, suggesting that sex determination occurs between 29 and 32 hao, which correspond to the developmental stages from the head lobe differentiation to spoon-shaped embryo stages. This also suggests that the master switch gene for sex determination of B. mori is expressed in females during this period and represses the male-specific mode of expression in sex-determining genes
The Standing Accretion Shock Instability in the Disk around the Kerr Black Hole
This paper is a sequel to our previous work for accretion onto a
Schwarzschild black hole and the so-called standing accretion shock instability
(SASI), in this paper we investigate non-axisymmetric perturbations for a Kerr
black hole. The linear and non-linear phases for the shock evolution are
analyzed in detail by both 2D general relativistic hydrodynamical simulations
and linear analysis. Since the structure of steady axisymmetric accretion flows
with a standing shock wave is very sensitive to the inner transonic flow, their
properties such as Mach numbers, which are important for the stability, depend
on the Kerr parameter very much. Although the essential features of the
instability do not differ from the previous results for the Schwarzschild black
hole, the frame dragging effects specific to the Kerr black hole is also
evident. Interestingly, the oscillation periods of the fundamental unstable
modes are dependent only on the shock radius irrespective of the injection
parameters.Comment: 27 pages, 12 figures, accepted in Ap
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