Biomedical subjects

Shuji Ishihara

Publications and source records attributed to Shuji Ishihara.

4 recordsLinked to original sources

PubMed2005

Turing pattern with proportion preservation.

Although Turing pattern is one of the most universal mechanisms for pattern formation, in its standard model the number of stripes changes with the system size, since the wavelength of the pattern is invariant. It fails to preserve the proportionality of the pattern, i.e. the ratio of the wavelength to the size, that is often required in biological morphogenesis. To get over this problem, we show that the Turing pattern can preserve proportionality by introducing a catalytic chemical whose concentration depends on the system size. Several plausible mechanisms for such size dependence of the concentration are discussed. Following this general discussion, two models are studied in which arising Turing patterns indeed preserve the proportionality. Relevance of the present mechanism to biological morphogenesis is discussed from the viewpoint of its generality, robustness, and evolutionary accessibility.

Animals↗

PubMed2005

Magic number 7+/-2 in networks of threshold dynamics.

Information processing by random feed-forward networks consisting of units with a sigmoidal input-output response is studied by focusing on the dependence of its outputs on the number of parallel paths M. It is found that the system leads to a combination of on-off outputs when M less or similar to 7, while for M greater or similar to 7, chaotic dynamics arises, resulting in a continuous distribution of outputs. This universality of the critical number M approximately 7 is explained by a combinatorial explosion, i.e., the dominance of factorial over exponential increase. The relevance of the result to biological problems is briefly discussed.

Animals↗

PubMed2005

Cross talking of network motifs in gene regulation that generates temporal pulses and spatial stripes.

Gene regulatory networks contain several substructures called network motifs, which frequently exist throughout the networks. One of such motifs found in Escherichia coli, Saccharomyces cerevisiae, and Drosophila melanogaster is the feed-forward loop, in which an effector regulates its target by a direct regulatory interaction and an indirect interaction mediated by another gene product. Here, we theoretically analyze the behavior of networks that contain feed-forward loops cross talking to each other. In response to levels of the effecter, such networks can generate multiple rise-and-fall temporal expression profiles and spatial stripes, which are typically observed in developmental processes. The mechanism to generate these responses reveals the way of inferring the regulatory pathways from experimental results. Our database study of gene regulatory networks indicates that most feed-forward loops actually cross talk. We discuss how the feed-forward loops and their cross talks can play important roles in morphogenesis.

Animals↗

PubMed2003

Pulse-wave velocity and cardiovascular risk factors in subjects with Helicobacter pylori infection.

BACKGROUND: Helicobacter pylori infection has been reported to correlate with the onset of cardiovascular diseases. However, the relationship between H. pylori infection and the development of arteriosclerosis has not been fully investigated. We performed a cross-sectional study to clarify the possible role of H. pylori infection in the development of arteriosclerosis. METHODS: The subjects were 996 cases who attended their annual medical check-up between April and August 2001. H. pylori infection status was determined by assaying serum anti-H. pylori immunoglobulin G antibodies. Total cholesterol, high-density lipoprotein cholesterol (HDLC), triglyceride, fasting blood glucose, hemoglobin A1c and leukocyte levels were determined. Arteriosclerotic parameters (systolic blood pressure (SBP), ankle brachial index (ABI) and pulse-wave velocity (PWV)) were measured non-invasively using an automatic device. The data for H. pylori-seropositive and -seronegative individuals were compared. RESULTS: Five hundred and seventy-three subjects (57.5%) were H. pylori-seropositive. After adjustment for sex, age, body mass index, and smoking and drinking habits, the HDLC levels of the seropositive and seronegative groups differed markedly (55.0 vs 58.0 mg/dL, P < 0.0001). Although there were no differences between the overall adjusted SBP and ABI values, the PWV was higher in H. pylori-seropositive than -seronegative young (<39 years old) individuals (heart-carotid PWV: 632.2 vs 589.7 cm/s, P = 0.027). These differences tended to disappear with aging. CONCLUSIONS: The degree of arterial stiffness in H. pylori-positive young subjects is higher than that in H. pylori-negative young subjects. However, no difference between the arterial stiffness values of H. pylori-seropositive and -seronegative elderly individuals was observed.

Adult↗