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*

Abstract

The organization center of Cynopspyrrhogaster was divided into Parts 1, 2 and 3 of equal size (0.3 x 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; 11, 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 11, each part induced dorsal mesoderm and neural tissues, the frequency being highest in Part 2 and lowest in Part 3. In 111, 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.The uninvaginated portion of the dorsal lip from early gastrulae organizes the trunk-tail (trunk or tail, or both) when transplanted or cultured in close contact with presumptive ectoderm from embryos of the same stage. The same portion acquires a head-organizing capacity after invagination or after a definite time of culture in isolation in Holtfreter's solution (1-6). These findings have been confirmed by others (7-10).Our results described above were unexpected, because the head organizer is located at the dorsal lip of the early gastrula (1 1). HAMA (12, 13) suggested that the motility of the organizer

Neural induction and antero-posterior patterning in the amphibian embryo: past, present and future

“…More recently, Kaneda and Hama [23] have shown that the trunk organizer does not acquire its final inducing ability until after involution during gastrulation. The presumptive head organizer before gastrulation behaves as an inducer of trunk structures and again only acquires its head-inducing characteristics gradually during gastrulation [24]. Taken together these reports suggest that definitive A-P axial properties in dorsal mesoderm are not determined until at least mid-gastrula stages.…”

Endoderm differentiation and inductive effect of activin‐treated ectoderm in Xenopus

“…In addition, Cynops activin-treated ectoderm induces a whole secondary axis (from head to tail) when transplanted into the VMZ of blastulae . These phenomena were also seen in Cynops presumptive endoderm of the DMZ next to axial mesoderm (Hama et al 1985;Yamamoto & Suzuki 1994;Ninomiya et al 1998). These reports suggest that activin-treated ectoderm is equivalent to endoderm of the DMZ and acts as an organizer in Cynops.…”

In vitro control of organogenesis and fundamental embryonic form by the peptide growth factor activin

“…The same region induces the formation of heads when it is precultured in saline for a specific period. 35 These results suggest that the age of the organizer influences the formation of the anteroposterior body pattern.…”