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M Asashima

Publications and source records attributed to M Asashima.

125 records · Page 7Linked to original sources
PubMed1990

Observations on cardiac ultrastructure of the adult Japanese newt, Cynops pyrrhogaster.

Investigation of atrial and ventricular cardiac ultrastructure by transmission and scanning electron microscopy of the adult Japanese newt, Cynops pyrrhogaster, has revealed some unique cell types and features in this amphibian. Typical urodelan-type thin trabeculae composed of myocytes with conventional architecture of loosely scattered myofibrils were observed. Scarce granules of variable size and density were seen in atrial myocytes, and some Purkinje-like fibers were observed. Unique structures included scattered endocrine-like cells with dense cytoplasmic granules in the epicardial spaces, a distinct granular cell found occasionally on the endocardial surface projecting into the lumen of the cardiac trabeculae, and peculiar granulated inclusions in the myoplasm. The function of these possible endocrine cells remains undetermined. It is important to characterize the heart of this species, as it has recently been proven to be an excellent model for prolonged experimental studies in vitro.

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PubMed1989

Developmental physiology of cardiac contraction in the Japanese newt in vivo and in vitro.

Development and differentiation of whole hearts of larvae of an experimental amphibian species, the Japanese newt (Cynops pyrrhogaster), were studied in vitro and in vivo with particular reference to cardiac contraction, its temperature sensitivity and morphology. Hearts cultured in the solid or flat state in plastic flasks for 27 days developed from stage 35 to stage 55 and corresponded closely to in vivo developing hearts with respect to morphologic criteria and temperature sensitivity of cardiac contraction. The peak rate of contraction at room temperature occurred after 20 days, both for cultured hearts in vitro and for in vivo hearts, which had reached stage 50 to 52 of development. Excised fractions of heart continued to beat at reduced rates for extended periods. Hearts cultured at late stages (50 to 55) continued to beat for 282 days, though the rate decreased to 1 bpm. Although cardiac contraction rate gradually declined during long-term culture, the sensitivity of this tissue to temperature change remained constant for 250 days. Thus, culture of the heart of this species should prove useful to the investigation of factors related to induction and developmental regulation of contractility.

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PubMed1989

Development of the heartbeat during normal ontogeny and during long-term organ culture of hearts of the newt, Cynops pyrrhogaster.

Development of cardiac contraction was investigated in the newt, Cynops pyrrhogaster, during normal development and in hearts maintained in long-term organ culture. In the embryos the heart began beating as early as stage 33. The heart rate increased up to stage 52 and then gradually decreased to the adult rate by stage 60. The heart rate showed a logarithmic temperature dependence. In organ-cultured hearts the pattern of heart rate depended on the stage at which the heart was explanted; cultured embryonic hearts showed a pattern of increase and decline similar to that seen in vivo, and hearts explanted near metamorphosis showed only a slow decline.

Animals↗
PubMed1989

Temperature-induced alterations in protein composition of newt papilloma cells.

Protein patterns of Japanese newt papilloma in vivo at low (4 degrees C), normal (10 degrees C, control) and elevated (30 degrees C) temperature were investigated by two-dimensional gel electrophoresis. There were nine protein spots in normal skin (skin specific spots: SSS) which did not exist in papillomas. At 10 degrees C, the papillomas possessed three specific protein spots (papilloma specific spots: PSS) which did not appear in normal skin. At the reduced environmental temperature, eight of the nine missing proteins in papillomas had reappeared by 12 weeks exposure. Differential responses in reappearance of SSS in papillomas varied with environmental temperature. The PSS generally were unchanged by environmental temperature modulation, although one specific protein disappeared at 12 weeks at 4 degrees C. Reappearance of normal SSS in papillomas occurred early in treatment and reflected only minor variations in high versus low temperature exposures. These data suggest that temperature-induced tumor regression may be associated with changes in protein composition.

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PubMed1989

Ultrastructural characterization of the spontaneous papilloma of Japanese newts.

The spontaneous epithelioma of the Japanese newt, Cynops pyrrhogaster, is a useful animal model for study of development and regression of papillomata of suspected viral origin. Therefore, ultrastructural studies of this cutaneous tumor were undertaken in order to characterize this model further. The ultrastructure of normal Cynops pyrrhogaster epidermis resembled teleost more than anuran epidermis. Surface cells of the bilayered stratum corneum were covered by micro-ridges and contained prominent nuclei, unlike the stratum corneum of mammals. Capillary endothelial cells contained unique small dense granules. Principal changes in tumors consisted of hyperplasia of stratum granulosum cells, increased melanin bodies in corneal cells, distorted configurations and aberrant location of outer corneal cells, which also demonstrated irregularity of micro-ridges and increased mucin and vacuole content. Intercellular spaces were enlarged between all cell types. Virus-like particles were observed in approximately 40 percent of tumors, particularly in the middle of the tumor.

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PubMed1985

Effects of temperature on papilloma growth in the newt, Cynops pyrrhogaster.

The effects of temperature on skin papillomas of newts (Cynops pyrrhogaster) were studied. Newts bearing these tumors were maintained for 30 weeks at 4 +/- 1 (S.E.), 10 +/- 1, 13 +/- 2, 25 +/- 1, and 30 +/- 1 degree. The diameters of the papillomas were measured externally. They decreased at 4, 25, and 30 degrees, and increased at 10 and 13 degrees. The effect of temperature on the tumor growth or regression began to appear from around the 10th week. Furthermore, when the temperatures were changed, it was possible to reverse the growth or regression of the tumors. Histologically, cell layers of the tumors became thin at 4, 25, and 30 degrees, but there were some differences between 4 and 25 or 30 degrees. The pigment layers became thick, and epidermal cells invaded dermal layer at 4 degrees, and clumps of cells separated from the surface of the tumors at 25 and 30 degrees. Mitotic indices were lower at 4, 25, and 30 degrees than in normal epidermis, but were about 3 times as high as normal tissue at 10 or 13 degrees. The relation between these results in the laboratory and seasonal fluctuations of these tumors in nature is discussed.

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PubMed1983

Effects of inducers on inner and outer gastrula ectoderm layers of Xenopus laevis.

Gastrula ectoderm, isolated from Xenopus laevis, was cultured in Holtfreter solution or modified Leibovitz medium (L-15) by the sandwich-method with or without inducer. The ectoderm (SD cell layers) consisted of two cell sheets, representing a superficial (S) and a deep (D) layer. In the L-15 medium rather than in Holtfreter solution, the two cell layers separate out into distinct cell masses. This difference in cell affinity under certain experimental conditions could indicate that the deep layer contains endodermal cells. However, an endodermal character of the deep layer can be ruled out by induction experiments with vegetalizing factor or dorsal blastopore lip as inducers. Under the influence of vegetalizing factor the outer as well as the inner ectoderm layer differentiated into mesodermal derivatives such as notochord and somites. The results of the experiments with dorsal blastopore lip as inducer indicate that both inner and outer ectoderm layers are responsive to the neural stimulus. The lower neural competence of the outer ectoderm layer observed by several authors in normogenesis is discussed with regard to the hypothesis about short distance diffusion of the neutralizing factor and/or close cell-to-cell contact between inducing tissue and ectodermal target cells.

Animals↗
PubMed1982

Radioiodination with 125I and reductive methylation with tritium of a vegetalizing inducer protein. Specific radio-activities and effect on biological activity.

An inducer protein, the vegetalizing factor, which causes amphibian ectoderm to differentiate into endoderm was labelled with carrier-free 125I (2000 Ci/m-Atom) to specific activities of 17-32 micronCi/microgram protein. The partial loss of the biological inducing activity is not caused by the iodination of the factor but is due to the oxidation and reduction steps in the iodination procedure. By reductive methylation with formaldehyde and [3H]NaBH4 under mild conditions the factor was labelled to specific activities of 0.8-2.3 micronCi/microgram protein depending on the specific activity of the [3H]NaBH4 (5-15 Ci/mmol). Under these conditions up to 25% of the amino groups of the protein were methylated without a reduction of the biological activity of the factor. The inducing activity of the protein was however considerably reduced, when under more stringent conditions 60-70% of the amino groups were methylated. It was shown by NMR spectroscopy that about one third of protein amino groups is dimethylated under these conditions. The factor could be labelled with N-(propionyloxy)succinimide without a loss of the biological activity, when very few amino groups were substituted. The experiments show that the factor can be labelled to high specific activity without loss of its inducing activity by reductive methylation, which is therefore the most suitable method.

Animals↗
PubMed1982

Seasonal and geographical changes of spontaneous skin papillomas in the Japanese newt Cynops pyrrhogaster.

The occurrence of spontaneous skin papillomas in Japanese newts (Cynops pyrrhogaster) from Niigata prefecture in Northern Japan was monitored over four seasons covering a period of 2 years. Of 13,613 newts, 249 were found to possess papillomas. The percentage of newts with papillomas was highest in autumn, ranging from 1.93 to 5.45% of the total average. These values were more than four times as high as values obtained in the other three seasons (0.16 to 0.50%). A total of 12,167 newts were collected from their natural environment in 10 prefectures of Japan in the autumn of 1980 and 1981. Newts collected from the northern, seaside prefectures had higher papilloma rates (1.00 to 5.45%) than did newts from the Southern, Pacific Ocean prefectures of Japan (0 to 0.27%). Male and female newts were affected equally often by the epitheliomas. Virus-like bodies, resembling herpes-type virus, were found in the cytoplasm of the epitheliomas. These virus-like bodies were not seen in the control epithelium of newts with normal skin and without papilloma or in nonaffected regions of newts with papilloma. It is suggested that tumor and virus are causally related.

Animals↗
PubMed1981

A vegetalizing inducing factor. Isolation and chemical properties.

A vegetalizing factor which induces the formation of endodermal and mesodermal organs in amphibian gastrula ectoderm was purified from chicken embryos. Preparative sodium dodecyl sulfate polyacrylamide electrophoresis and gel permeation chromatography on sephadex with different eluants were employed. In buffer containing 6 M urea the molecular weight of the factor was estimated to about 28 000-30 000. In buffer containing sodium dodecyl sulfate (SDS) the factor partially dissociates to smaller polypeptide chains. Because an equilibrium between molecules of different size is established, SDS-containing buffers are not suitable for preparative purposes. In 50%-70% formic acid the factor completely dissociates into smaller peptide chains (Mr about 13 000-15 000). Furthermore, very little absorption of the factor to the gel matrices or glass surfaces is observed in formic acid. The final purification can be achieved by high-performance gel permeation chromatography with glycerolpropyl-treated silica gel as column packing and 50% formic acid as eluant.

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PubMedDate not supplied

Spontaneous thyroid-containing teratoma associated with impaired development in the African clawed frog, Xenopus laevis.

Teratomas are rare in amphibians and the neoplasm described here, which had a significant thyroid carcinoma component, is the first tumour of this type to be reported in Xenopus laevis. The thyroid component contained moderately to well-differentiated acinar glands showing much hyperplasia, dysplasia, and reduced and distorted colloid reservoirs. Cartilaginous, neural, muscular, mesenchymal and gut-like epithelial components were also observed in this ventral mediastinal neoplasm, indicating aberrant proliferation from all three germ layers. This teratoma was only one abnormality in a complex of developmental changes, followed for 28 months, which appeared in a single generation of sibling 2-week-old Xenopus larvae. Two hundred larvae produced by an apparently normal adult pair initially showed ocular defects, including microphthalmia, anophthalmia and tumours projecting near the eyes. During further development up to 28 months, mediastinal tumours developed in nine frogs; these tumours were associated with reduced growth, the frogs reaching only 13-20% of normal weight, and greatly enhanced ventral pigmentation.

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