Biomedical subjects

Y Iwasa

Publications and source records attributed to Y Iwasa.

At least 73 records · Page 4Linked to original sources

PubMed1998

Score-dependent fertility model for the evolution of cooperation in a lattice.

The evolution of cooperation is studied in a lattice-structured population, in which each individual plays the iterated Prisoner's Dilemma game with its neighbors. The population includes Tit-for-Tat (TFT, a cooperative strategy) and All Defect (AD, a selfish strategy) distributed over the lattice points. An individual dies randomly, and the vacant site is filled immediately by a copy of one of the neighbors in which the probability of colonization success by a particular neighbor is proportional to its score accumulated in the game. This "score-dependent fertility model" (or fertility model) behaves very differently from score-dependent viability model (viability model) studied in a previous paper. The model on a one-dimensional lattice is a analysed by invasion probability analysis, pair-edge method mean-field approximation, pair approximation, and computer simulation. Results are: (1) TFT players come to form tight clusters. When the probability of iteration w is large, initially rare TFT can invade and spread in a population dominated by AD, unlike in the complete mixing model. The condition for the increase of TFT is accurately predicted by all the techniques except mean-field approximation; (2) fertility model is much more favorable for the spread of TFT than the corresponding viability model, because spiteful killing of neighbors is favored in the viability model but not in the fertility model; (3) eight lattice games on two-dimensional lattice with different assumptions are examined. Cooperation and defects can coexist in the models of deterministic state change but not in the models of stochastic state change.

Biological Evolution↗

PubMed1998

Runaway ornament diversity caused by Fisherian sexual selection.

Fisher's runaway process of sexual selection is potentially an important force generating character divergence between closely related populations. We investigated the evolution of multiple female preferences by Fisher's runaway process. There are two outcomes of runaway. The first is the evolution of mate preference to a stable equilibrium. This evolution occurs if the benefits of mate choice are sufficiently large relative to the cost of choice. Alternatively, mate preferences evolve cyclically. The rate and pattern of cyclic evolution depends primarily on the individual cost of choice and epistasis in the joint cost of choice. If there are small differences in natural selection (e.g., predation risk) between populations, cyclic evolution quickly leads to divergence in mate preferences and sexual ornaments and so to sexual isolation.

Animals↗

PubMed1998

Prognostic factors in uterine carcinosarcoma: a clinicopathologic study of 25 patients.

BACKGROUND: Carcinosarcoma (malignant mixed mullerian tumor) of the female genital tract is a highly malignant neoplasm. The tumor stage and histologic grade of the carcinomatous component are among the important prognostic indicators cited in the literature for this tumor. METHODS: Twenty-five patients with uterine carcinosarcoma at 4 hospitals in the Kyoto and Nara areas of Japan were studied retrospectively. The clinicopathologic and immunohistochemical data including p53, bcl-2, Ki-67, and proliferating cell nuclear antigen (PCNA) staining were analyzed using univariate and multivariate analysis with the Cox proportional hazards model to investigate potential prognostic indicators for this neoplasm. RESULTS: The 5-year survival rate was 36.4% for all stages, 62.3% for Stage I, and 0% for Stages II-IV. From the univariate analysis, stage (P = 0.0001), endometrioid adenocarcinoma as a carcinomatous component (P = 0.0006), age (P = 0.0355), and a heterologous sarcomatous component (P = 0.0421) were found to be prognostically significant for patient survival. Stage was the only independent significant factor in the multivariate analysis (t = 2.212). None of the other factors (history of pregnancy and gestation, gross appearance of the tumors, grade of the carcinomatous component, mitotic count of the sarcomatous component, Ki-67 and PCNA reactivity, or p53 or bcl-2 positive staining) was found to be a significant prognostic indicator. CONCLUSIONS: Stage appears to be the only definite independent prognostic indicator of survival in patients with uterine carcinosarcoma. It is uncertain whether age, endometrioid adenocarcinoma as a carcinomatous component, or absence of a heterologous component in the sarcomatous area are prognostic factors. Immunohistochemical expression of p53, bcl-2, Ki-67, or PCNA is not a prognostic indicator. The immunohistochemical results of the current study may support the hypothesis of a common stem cell origin of this tumor.

Adult↗

PubMed1998

Cell-cell adhesion in limb-formation, estimated from photographs of cell sorting experiments based on a spatial stochastic model.

We developed a new method to estimate the magnitude of differential cell-cell adhesion of two tissues based on the spatial patterns in cell-sorting experiments, and applied it to experimental data on progress-zone cells of avian limb bud at stages 20-26. The change in cell distribution in the experiment was recorded, and statistics qB/B for the degree of cell sorting was calculated from the photographs. Based on extensive computer simulations of spatial Markov processes on a 2-D lattice, we derived a formula for qB/B increasing with time. Using least square fitting, differential adhesion A and cell motility m are estimated from the time series data of qB/B obtained from the experiment. The estimated A was close to 0 (the spatial pattern remained random) if the mixed cells were from two tissues of the same stage. If the mixed cells were from different stages, and the estimated A was positive (cell sorting occurred). Estimated A increased with the difference in the stage number of the two tissues from which the cells were sampled. This result can be explained both by the stage-specific change in adhesion molecules and by a linear increase (or decrease) in the amount of adhesion molecules on cell surface.

Animals↗

PubMed1998

Extinction rate of a population under both demographic and environmental stochasticity.

We examined the asymptotic rate of population extinction beta when the population experiences density-dependent population regulation, demographic stochasticity, and environmental stochasticity. We assume discrete-generation population dynamics, in which some parameters fluctuate between years. The fluctuation of parameters can be of any magnitude, including both fluctuation traditionally treated as diffusion processes and fluctuation from catastrophes within a single scheme. We develop a new approximate method of calculating the asymptotic rate of population extinction per year, beta=integralinfinity0 exp(-x) u(x) dx, where u(x) is the stationary distribution of adult population size from the continuous-population model including environmental stochasticity and population-regulation but neglecting demographic stochasticity. The method can be regarded as a perturbation expansion of the transition operator for population size. For several sets of population growth functions and probability distributions of environmental fluctuation, the stationary distributions can be calculated explicitly. Using these, we compare the predictions of this approximate method with that using a full transition operator and with the results of a direct Monte Carlo simulation. The approximate formula is accurate when the intrinsic rate of population increase is relatively large, though the magnitude of environmental fluctuation is also large. This approximation is complementary to the diffusion approximation.

Adult↗

PubMed1998

The conflict theory of genomic imprinting: how much can be explained?

In some mammalian genes, paternally and maternally derived alleles are expressed differently: this phenomenon is called genomic imprinting. Several-explanations have been proposed for the observed patterns of genomic imprinting, but the most successful explanation is the genetic conflict hypothesis--natural selection operating on the gene expression produces the parental origin-dependent gene expression--because the paternally derived allele tends to be less related to the siblings of the same mother than the maternal allele and hence the paternal allele should evolve to be more aggressive in obtaining maternal resources. The successes and failures of this argument have been examined in explaining the observed patterns of genomic imprinting in mammals. After a brief summary of the observations with some examples, a quantitative genetic model describing the evolution of the cis-regulating element of a gene affecting the maternal resource acquisition was presented. The model supports the verbal argument that the growth enhancer should evolve to show imprinting with the paternal allele expressed and the maternal allele inactive, whereas a growth suppressor gene tends to have an inactive paternal allele and an active maternal allele. There are four major problems of the genetic conflict hypothesis. (1) Some genes affect embryonic growth but are not imprinted (e.g., Igf1), which can be explained by considering recessive, deleterious mutations on the coding regions, (2) A gene exists that shows the pattern that is a perfect reversal (Mash2), which is needed for placental growth, and yet has an active maternal allele and an inactive paternal allele. This can be explained if the overproduction of this gene causes dose-sensitive abortion to occur in early gestation. (3) Paternal disomies are sometimes smaller than normal embryos. This is a likely outcome of evolution if imprinted genes control the allocation between placenta and embryo by modifying the cell developmental fate. (4) Genes on X chromosomes do not follow the predictions of the genetic conflict hypothesis. For genes on X chromosomes, two additional forces of natural selection (sex differentiation and dosage compensation) cause genomic imprinting, possibly in the opposite direction. Available evidence suggests that these processes are stronger than the natural selection caused by female multiple mating. Finally, the same formalism of evolution can handle an alternative nonconflict hypothesis: genomic imprinting might have evolved because it reduces the risk of the spontaneous development of parthenogenetic embryo, causing a serious threat to the life of the mother (ovarian time bomb hypothesis). This hypothesis can also explain major patterns of genomic imprinting. In conclusion, the genetic conflict hypothesis is very successful in explaining the observed patterns of imprinting for autosomal genes and probably is the most likely evolutionary explanation for them. However, for genes on X chromosomes, other processes of natural selection are more important. Considering that a nonconflict hypothesis can also explain the patterns in principle, we need a quantitative estimate of various parameters, such as the rate of dose-dependent abortion, the degree of female promiscuity, and the rate of spontaneous development of the parthenogenetic embryo, in order to make judgments on the relative importance of different forces of natural selection to form genomic imprinting.

Abortion, Veterinary↗

PubMed1998

High-risk human papillomavirus infection and overexpression of p53 protein in squamous cell carcinoma of the esophagus from Japan.

The present study was undertaken in order to investigate the possible involvement of high-risk human papillomavirus (HPV; types 16 and 18) or the overexpression of p53 protein in 123 Japanese patients with esophageal squamous cell carcinoma (SCC) from five different institutions. We detected HPV DNA in 30.1% (37/123) by in situ hybridization (ISH). Of these 123 cases, HPV type 16 was detected in 22 cases and HPV type 18 in 23 cases. In addition, HPV types 16 and 18 were detected simultaneously in eight cases. We found an almost similar incidence of HPV infection at five different places in Japan. Then, among these patients, 24 fresh tumor samples were also examined for screening the presence of HPV DNA using dot blot hybridization (DBH) and polymerase chain reaction (PCR). We detected HPV DNA in 20.8% (5/24) by DBH and in 12.5% (3/24) by PCR. P53 protein overexpression was found in 34.1% (43/123) by immunohistochemistry (IHC). Furthermore, in 43 cases from Kochi Medical School, the group positive for p53 antibody statistically showed worse survival rate than the group negative for both HPV DNA and p53 antibody. Judging from these results obtained in the present study, HPV infection and p53 overexpression are frequently detected and involved in the carcinogenesis of esophageal SCC in Japan. We also found that no significant geographical difference of both HPV infection and p53 overexpression of esophageal SCC was seemingly present in Japan.

Aged↗

PubMed1998

Degeneration of tooth germ in the developing dentition of the gray short-tailed opossum (Monodelphis domestica).

The aim of this study was to examine the developmental aspects of the dental lamina and the tooth germ of the marsupial opossum (Monodelphis domestica), and to clarify the dental formula of this animal. Specimens were 12-, 16-, and 18-d-old opossums. 3-D reconstructions were constructed from frontal serial sections. In these animals, the tooth germs of the deciduous maxillary and mandibular canine, deciduous third premolar and first molar, and the deciduous maxillary first incisor and second molar had a successional dental lamina and a replacement tooth germ. The tooth germ of the deciduous maxillary fourth incisor and the mandibular first incisor were reduced. The dental lamina was continuous in each jaw except for the deciduous maxillary first incisor. The first dentition (deciduous dentition) remained as the permanent dentition on the deciduous maxillary first incisor, and the deciduous maxillary and mandibular canine and first molar. The maxillary fourth incisor and the mandibular first incisor were the second dentition (successional dentition). Only the deciduous third premolars were replaced. These results showed monophyodonty caused by both deciduous and replacement tooth germ degeneration.

Animals↗

PubMed1998

Effect of multidisciplinary treatment with high dose rate intraluminal brachytherapy on survival in patients with unresectable esophageal cancer.

BACKGROUND: Since carcinoma of the esophagus is usually diagnosed at an advanced stage, many cases of esophageal cancer are beyond possible radical resection and only palliative treatment can be performed in such cases. Therefore, a great deal of discussion has taken place concerning indications for treatment modality, and various procedures have been performed to palliate such patients. The prognosis for such patients is still poor, even though many kinds of palliation have already been developed and applied. To improve the prognosis of such patients we developed a multidisciplinary treatment which includes high dose rate intraluminal brachytherapy (HDR-ILBRT) and evaluated its effectiveness, especially the HDR-ILBRT component. PATIENTS AND TREATMENT METHODS: Sixty-six patients with unresectable esophageal cancer enrolled in this study. Twenty-seven patients underwent bypass operations. Seven of the 27 patients received external irradiation only (group BE), 11 received external irradiation and HDR-ILBRT (group BEH), while the remaining 9 did not receive radiotherapy (group B). Another 39 patients without bypass operations were all treated with radiotherapy, 22 with external irradiation only (group E) and 17 were treated with external irradiation and HDR-ILBRT (group EH). After completion of radiotherapy, all patients received chemotherapy with 5-FU (2,500 mg/body) and CDDP (100 mg/body). RESULTS: Mean survival time and the 5-year survival rate of group BEH (13.3 +/- 1.5 months and 20%) were significantly improved compared with group BE + B (p < 0.05). In the patients without bypass operations, there were significant differences in the mean survival time and the 3-year survival rate in groups EH and E (group EH 16.5 +/- 2.5 months, 21.8%, group E 9.0 +/- 1.3 months, 0%, p < 0.05). The bypass operation itself and chemotherapy did not significantly affect the prognosis of patients with unresectable esophageal cancer. CONCLUSION: These results strongly suggest the use of HDR-ILBRT, as a component of multidisciplinary treatment for unresectable esophageal cancer, was significantly effective and HDR-ILBRT contributed to improve outcomes in patients with advanced esophageal cancer. HDR-ILBRT should be established as a component of treatments for unresectable esophageal cancer.

Aged↗

PubMed1998

The function and structure of the marsupial enamel.

The aims of this study are to clarify the structure of tubular enamel and the function of enamel tubules on the marsupial of opossum (Monodelphis domestica). Almost all enamel prisms, surrounded by interprismatic enamel, ran obliquely from the dentinoenamel junction (DEJ), and bent near the enamel surface. The enamel tubules are distributed in both enamel prisms and the interprismatic enamel near the DEJ. From the middle to the surface of the enamel, one enamel tubule ran within a single enamel prism. Most of enamel tubules continued from the DEJ to near the enamel surface. It is suggested that each enamel tubule developed in relation to one ameloblast. The fibers of odontoblastic process penetrated the DEJ from the dentinal tubules into the enamel tubules, and some branched across the enamel prisms. The odontoblastic process may be actively cross into the ameloblastic layer and may be involved in the formation of enamel tubules. After in vivo injection of tetracycline, tetracycline labeling showed that the odontoblastic tubules continued to enamel tubules. And strontium was detected in enamel tubules from the DEJ to the enamel surface, as was the dentinal tubules. In conclusion, there was active transport by the odontoblast and it's process through the enamel tubules.

Animals↗

PubMed1997

The evolution of cooperation in a lattice-structured population.

The evolution of cooperation among unrelated individuals is studied in a lattice-structured habitat, where individuals interact locally only with their neighbors. The initial population includes Tit-for-Tat (abbreviated as TFT, indicating a cooperative strategy) and All Defect (AD, a selfish strategy) distributed randomly over the lattice points. Each individual plays the iterated Prisoner's Dilemma game with its nearest neighbors, and its total pay-off determines its instantaneous mortality. After the death of an individual, the site is replaced immediately by a copy of a randomly chosen neighbor. Mathematical analyses based on mean-field approximation, pair approximation, and computer simulation are applied. Models on one and two-dimensional regular square lattices are examined and compared with the complete mixing model. Results are: (1) In the one-dimensional model, TFT players come to form tight clusters. As the probability of iteration w increases, TFTs become more likely to spread. The condition for TFT to increase is predicted accurately by pair approximation but not by mean-field approximation. (2) If w is sufficiently large, TFT can invade and spread in an AD population, which is impossible in the complete mixing model where AD is always ESS. This is also confirmed by the invasion probability analysis. (3) The two-dimensional lattice model behaves somewhat in between the one-dimensional model and the complete mixing model. (4) The spatial structure modifies the condition for the evolution of cooperation in two different ways: it facilitates the evolution of cooperation due to spontaneously formed positive correlation between neighbors, but it also inhibits cooperation because of the advantage of being spiteful by killing neighbors and then replacing them.

Animals↗

PubMed1997

The well-balanced nucleoside-nucleotide mixture "OG-VI" for special medical purposes.

Nucleotides and nucleosides are essential components in all cells. However, nucleotides have not been supplied in parenteral nutrition regimens. We developed a well-balanced nucleoside-nucleotide mixture "OG-VI" and examined its effect in animals under some stressed conditions. OG-VI was composed of 30 mmol/l of inosine, 30 mmol/l of guanosine monophosphate, 30 mmol/l of cytidine, 22.5 mmol/l of uridine and 7.4 mmol/l of thymidine. The whole body protein turnover increased significantly in rats receiving total parenteral nutrition (TPN) with OG-VI solution after 70% hepatectomy, compared with rats receiving normal TPN without OG-VI (122.1 +/- 20.9 mgN.kg-1.h-1 vs. 97.4 +/- 10.1 mgN.kg-1.h-1, P < 0.01, n = 10). OG-VI significantly enhanced protein synthesis while it did not decrease protein breakdown. The effect of OG-VI on myocardium after hypoxic challenge was also examined in rats. The creatine phosphate (PCr)/inorganic phosphate (Pi) was decreased in normal rat myocardium after hypoxic challenge. However, in the rats administered OG-VI, PCr/Pi was maintained at baseline level and did not decrease after hypoxia. There was no significant change in the level of adenosine triphosphate (ATP) between before and after hypoxic challenge in myocardium of the rats administered OG-VI. In the rats receiving normal saline, instead of OG-VI, the ATP level decreased significantly after hypoxic challenge (4132 +/- 276 nmol/g tissue, n = 3, vs. 3439 +/- 465 nmol/g tissue, n = 5, P < 0.05). These data suggested that the well-balanced nucleoside-nucleotide mixture, OG-VI improved nitrogen metabolism and might stimulate synthesis of high-energy phosphate in recovery after severe surgical stress.

Animals↗

PubMed1996