Tadao Hama

Inductive Capacities for the Dorsal Mesoderm of the Dorsal Marginal Zone and Pharyngeal Endoderm in the Very Early Gastrula of the Newt, and Presumptive Pharyngeal Endoderm as an Initiator of the Organization Center*

The organization center of Cynops pyrrhogaster was divided into Parts 1, 2 and 3 of equal size (0.3×0.4 mm2) with presumptive fates as pharyngeal, pharyngeal+prechordal+trunk notochord, and trunk‐tail notochord, respectively. Movements and changes in size and shape of each part were followed through gastrulation. Differentiation tendencies of each part were examined under three conditions: I, isolated; II, sandwiched with presumptive ectoderm; 111, sandwiched with presumptive ectoderm after preculture in isolation for various times. In I, Parts 2 and 3 differentiated into dorsal mesoderm. In II, each part induced dorsal mesoderm and neural tissues, the frequency being highest in Part 2 and lowest in Part 3. In III, Parts 1 and 2 realized their presumptive fates, through changes in inductive capacities from trunk‐tail to head. This change progressed rapidly in Part 1, and slowly in Part 2. Part 3 required induction by neighbouring Part 2 to realize its presumptive fate. Changes of inductive capacity of Parts 1 and 2 respectively, were chronologically similar in normal development and in preculture experiments. Lastly, the primary presumptive pharyngeal zone at blastula was proposed to act as an initiator of the organization center, its programmed information being transmitted to Part 2, and then to Part 3.

Transformation of amphibian iridophores into melanophores in clonal culture.

Abstract Iridophores isolated from bullfrog tadpoles were successfully cloned. In primary culture, the iridophores showed contraction of cell bodies by the addition of alkali-treated ACTH. The disappearance of reflecting platelets occurred in proliferating iridophores and many small black melanin granules were synthesized in the cells. The chromatophores now showed melanin dispersion by the addition of the above hormone. The findings suggest that iridophores transform into melanophores in vitro .

Structural change of pterinosome (pteridine pigment granule) during the Xanthophore differentiation of Oryzias fish.

Structural changes in pterinosomes found in xanthophores were studied electron microscopically using 5, 6, 7, 8, and 9 mm-long stages of larvae of Oryzias latipes. Herein designated types G-1 to G-5 pterinosomes appeared most abundantly, corresponding to the respective stage in the above sequence. They were round or ellipsoidal. Types G-1 and G-2 had clear limiting membranes and inner fibrous structures. Type G-2 had a few superficial lamellae. Type G-3 was characterized by multiple, concentric lamellae and a central fibrous aggregate. Type G-4 was discernible from type G-3 by the lack of a central aggregate. Type G-5 lacked or contained only fragments of lamellae. Each type of pterinosome at the respective stage was counted. Thus, it was concluded that type G-1 was successively transformed into types G-4 and/or G-5.

ELECTRON MICROSCOPIC DEMONSTRATION OF TYROSINASE IN PTERINOSOMES OF THE FROG XANTHOPHORE, AND THE ORIGIN OF PTERINOSOMES*

In the frog, Rana japonica, the successive appearance of types I, II and III pterinosomes, which were defined according to the degree of lamellar structure, is in keeping with the xanthophore differentiation at the larval stage, but these three types coexist in a single xanthophore in the adult. An intense tyrosinase reaction was found in type I–II intermediate form in the larval and adult xanthophores, but it was rarely observed in types I and III. A tyrosinase reaction was always found in the GERL (Golgi‐associated Endoplasmic Reticulum) of larval and adult xanthophores, and it was similarly evident in small Golgi vesicles which were separated from the GERL and dispersed in the cytoplasm. The above findings suggest that tyrosinase and pterinosome originate from different parts of the cytoplasm. The hypothesis that small Golgi vesicles are transported to the tyrosinase‐negative premelanosomes involved in the origin of the melanosome is also applicable to the origin of pterinosomes.

The effect of aging on the neural competence of the presumptive ectoderm and the effect of aged ectoderm on the differentiation of the trunk organizer inCynops pyrrhogaster

SummaryThe effect of aging on the neural competence of the presumptive ectoderm of the early gastrula, and the effect of aged ectoderm on the differentiation of the still uninvaginated dorsal blastoporal lip at the small yolk-plug stage — representing the trunk organizer — were examined by the sandwich method inCynops pyrrhogaster.The presumptive ectoderm to be used as reaction system was taken from 0 to 36 h exogastrulae obtained by operation at the early gastrula stage and combined with trunk organizer. In the 0 to 12 h explants typical trunktail structures were formed. With further aging of the presumptive ectoderm a decrease in frequency of spinal cord, notochord, and muscle and a simultaneous increase in frequency of mesenchyme and mesothelium were observed. In the 30 and 36 h explants neural competence had largely disappeared, the frequency of notochord and muscle become very low and their differentiation very poor, whereas the frequency of mesenchyme and mesothelium reached very high levels.We infer a reciprocal relationship between the induced spinal cord and the differentiation of notochord and muscle, as well as a transformation of notochordal material into mesenchyme and mesothelium under the influence of the aged ectoderm. The mode of action of the trunk organizer in normal development is discussed.

Electron microscopic study on the xanthophore differentiation in Xenopus laevis, with special reference to their pterinosomes

Structural changes in pterinosomes and behavior of cytoplasmic inclusions in the process of xanthophore differentiation were studied electron microscopically using Xenopus laevis . At the early stage of xanthophore development, type I pterinosomes with clear limiting membranes, inner amorphous materials, and fine-fibrous structures, well developed nucleolus, mitochondria, and Golgi bodies, and a large number of polysomes are seen. Characteristic at the transitional stage are type II pterinosomes with indistinct limiting membranes and a few lamellae, and the simultaneous appearance of lipid droplets and glycogen particles. At the late stage, type III pterinosomes have many concentric lamellae. Their limiting membranes are not distinguished from the outermost lamellae. On the basis of counts of pterinosomes according to type at various stages, it was concluded that there is successive transformation from type I to type III. Adult xanthophores contain all types of pterinosomes in single cells, in contrast to larval xanthophores. A different mechanism of pterinosome genesis in larval and in adult xanthophores is suggested.

Guanine formation in isolated iridophores from bullfrog tadpoles.

Iridophores were isolated from the peritoneum of bullfrog tadpoles by the method of trypsin digestion followed by Ficoll density gradient centrifugation. Guanine and hypoxanthine were found in the isolated iridophores. The incorporation of the label of [3H]guanosine into guanine was demonstrated using the isolated iridophores.

Structural changes of drosopterinosomes (red pigment granules) during the erythrophore differentiation of the frog, Rana japonica, with reference to other pigment-containing organelles

SummaryStructural changes in drosopterinosomes (red pigment granules) of Rana japonica in the process of erythrophore differentiation were studied by light and electron microscopy. On the basis of the degree of pterinosome differentiation, three types can be recognized: Typ-I drosopterinosomes appear first during metamorphosis and have clear limiting membranes and amorphous materials within. Those of type-II are found in abundance shortly after metamorphosis and have inner structures, consisting of fibrillae and/or small lamellae in dense concentric arrangement. Type-III is found abundantly in adults and acquires an almost homogeneously electron-dense mature morphology, probably from the deposition of electron-dense materials. On the basis of counts of pterinosomes, a successive transformation from type I to III is suggested. The differences among red drosopterinosomes, yellow sepiapterinosomes in xanthophore and melanosomes are not always distinguishable electron microscopically. Discrimination is possible by careful examination of lamellar patterns characteristic of the respective granules and by a simultaneous application of light and electron microscopy. From this viewpoint, a re-evaluation of the identification of granules previously reported was effected.

ULTRAMICROSCOPIC STUDY OF THE DEVELOPMENTAL CHANGE OF THE XANTHOPHORE IN THE FROG, RANA JAPONICA WITH SPECIAL REFERENCE TO PTERINOSOMES*

Structural change in pterinosomes and the behavior of cytoplasmic inclusions in the process of xanthophore differentiation were studied electron microscopically using Rana japonica. At the early stage of xanthophore development, type I pterinosomes had clear limiting membranes and were empty or amorphous within. The nucleus and cytoplasm were characterized by a well‐developed nucleolus, mitochondria and Golgi bodies, and a large number of polysomes. At the middle stage, type II pterinosomes had indistinct limiting membranes and a few lamellae. Lipid droplets appeared almost concurrently with glycogen particles in the cytoplasm. At the later stage, type III pterinosomes had concentrically arranged lamellae, lacking clear limiting membranes. Thus, the successive transformation from types I to III was concluded. Adult xanthophores contained types I to III pterinosomes in each cell. A different mechanism is suggested of the differentiation of pterinosomes between the larval and the adult xanthophores.

Tyrosinase activity of the melanin and pteridine granules in goldfish chromatophores

Abstract 1. 1. The melanin granules within the melanophore and the pteridine granules within the erythrophore in the adult skin of four colored varieties (black moor, red, white and calico) of goldfish, Carassius auratus L were separated by the method of low-speed density gradient centrifugation. 2. 2. It has been demonstrated that the melanin granules are free of tyrosinase activity and probably of pteridine derivatives and that the pteridine granules are the carriers of pteridine derivatives and tyrosinase. 3. 3. The location of tyrosinase has been demonstrated morphologically: (1) the melanization of erythrophores has been induced; (2) further melanization did not occur in the melanophores; (3) no amelanotic melanophores have been observed.