ABSTRACT
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.
ABSTRACT
The 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.
ABSTRACT
The exact localization of the presumptive trunk organizer was determined by means of vital staining at the initiation of gastrulation (0 h embryo) and subsequently in 6, 9, 12 and 24 h embryos.The progressive changes in the self-differentiation and inductive capacity of the trunk organizer were studied in isolation cultures (sitting drop) and in sandwich cultures with competent gastrula ectoderm. In the 0 and 6 h embryo cultures the excised trunk organizer predominantly formed atypical ectoderm. A dramatic change in differentiation and inductive capacity occurred in the 9 h embryo. The positive cases - 83% of the isolation and 50% of the sandwich cultures - mainly formed notochord and somites, accompanied by spinal cord and hindbrain in the sandwich cultures. Although no further change in self-differentiation occurred from that time onwards, a gradual increase in inductive capacity was recognized.
ABSTRACT
The effect of aging on the neural competence of the presumptive ectoderm in gastrulae of Cynops pyrrhogaster and the effect of aged ectoderm on differentiation of the extreme posterior of the archenteric roof in the slit-blastopore stage were examined by a sandwich method in which this organizer was wrapped in the presumptive ectoderm taken from the 0- to 42-hr aged exogastrulae. Vital staining showed that this organizer becomes mainly tail notochord. Therefore it should be called tail or trunk-tail organizer. In 0- to 18-hr explants, typical trunk-tail structures were formed. With further aging of the presumptive ectoderm, a decrease of spinal cord and muscle with a concomitant increase of mesenchyme and mesothelium was observed. In 36- (corresponding to the slit-blastopore-initial neural stage) and 42-hr explants, neural competence had disappeared markedly. The notochord appeared in all explants, indicating this organizer is more firmly determined than the uninvaginated dorsal lip in small yolk-plug stage. Conclusively, this organizer does not play an important role in the induction of the neural plate, but induces the tail in normal development.
ABSTRACT
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.
