Studies on the Formation and State of Determination of the Trunk Organizer in the Newt, Cynops Pyrrhogaster. Ii. Inductive Effect From the Underlying Cranial Archenteron Roof

Abstract

Mesoderm formation in the presumptive trunk organizer was analyzed in gastrulae of Cynops pyrrhogaster. The presumptive trunk organizer showed little or no mesodermal differentiation in the beginning gastrula (0 h embryo). But as soon as the presumptive trunk organizer came into contact with the newly invaginated cranial archenteron roof, it rapidly formed mesoderm. This suggests that this differentiation was brought about by an inductive effect of the underlying cranial archenteron roof. For investigation of this possibility, the presumptive trunk organizer of 0 h embryos (Tr‐0) and the newly invaginated cranial archenteron roof (presumptive pharyngeal endoderm and prechordal plate) of successive stages were cultured in isolation and by the sandwich technique. The newly invaginated presumptive pharyngeal endoderm and prechordal plate had no effect on mesoderm formation of the presumptive trunk organizer, and mesodermal differentiation of the combinations was similar to that of the Tr‐0 alone. On the other hand, results showed that the prechordal plate, which came into contact with the still uninvaginated presumptive trunk organizer, stimulated dorsalisation of the weakly mesodermized trunk organizer. Based on these results, the stepwise process of mesoderm formation in the trunk organizer is discussed.

Comparative study of sequential expression of the organizer‐related genes in normal Cynops pyrrhogaster embryos and mesodermalized ectoderm

“…This means that gsc is expressed in the lower part of the dorsal marginal zone (Nieuwkoop center in the X. laevis embryo) and then in head mesoderm (Blumberg et al 1991). gsc seems to play a role in dorsal mesoderm induction rather than in mesoderm differentiation itself, because only the lower dorsal marginal zone has a dorsal mesoderm‐inducing activity at early C. pyrrhogaster gastrula and its activity disappears quickly after involution (Kaneda 1980; Suzuki et al 1984; Yamamoto & Suzuki 1994).…”

Gastrulation and pre-gastrulation morphogenesis, inductions, and gene expression: Similarities and dissimilarities between urodelean and anuran embryos

“…It is clear that notochord/somite self-differentiation capacity and trunk-tail neural-inducing activity of the presumptive notochord is evoked from the mid-gastrula stage onward (Kaneda and Hama, 1979). The notochord-and Cybra-inducing activity of the LDMZ disappears soon after involution or culture in vitro (Kaneda, 1980(Kaneda, , 1981Suzuki et al, 1984;Kaneda et al, 2002; see Fig. 10).…”

“…Although the embryonic stage, isolation size, spatial localization and methods of identifying the self-differentiation and organizing capacities vary among studies according to the defining criteria used, the self-differentiation and organizing activities of the early gastrula DMZ have been extensively analyzed in many urodeles (e.g., Spemann and Mangold, 1924;Holtfreter, 1938a;Holtfreter-Ban, 1965;Kaneda and Hama, 1979;Kaneda, 1980Kaneda, , 1981Slack, 1984;Cleine and Slack, 1985;Hama et al, 1985;Delarue et al, 1992;Yamamoto and Suzuki, 1994;Imoh et al, 1998;Kaneda et al, 2002Kaneda et al, , 2009 and in anura species (e.g., Holtfreter, 1938b;Smith and Slack, 1983;Gerhart, 1990, 1991;Shih and Keller, 1992;Domingo and Keller, 1995;Lane and Keller, 1997;Manes and Campos Casal, 1997;Fujii et al, 2002). By inserting the DLP into the blastocoel, earlier experiments revealed that the DLP of the early gastrula has secondary axis organizing activity in which the inserted DLP differentiates into notochord, somites and endoderm, while the secondary neural axis originates from the host embryo (e.g., Spemann and Mangold, 1924).…”

The formation of the mesoderm in urodelean amphibians VI. The self-organizing capacity of the induced meso-endoderm

“…Although it is difficult to interpret the course of development pursued, in particular that of the gastrulation process, from the ultimate structure of the differentiated larva, it seems likely that dorsal archenteron formation occurred only in cases with complete axis formation (type 4), since prechordal mesoderm formation seems indispensable for this process (see Hoessels 1957;Kaneda and Hama 1979;Kaneda 1980Kaneda , 1981Kaneda and Suzuki 1983). In the case of trunk-tail formations (type 3), the meso-endoderm may have moved inward at the boundary of the two moieties without extensive archenteron formation.…”