Two essential processes in the formation of a dorsal axis during gastrulation ofCynops embryo

Abstract

The isolated upper marginal zone from the initial stage ofCynops gastrulation is not yet determined to form the dorsal axis mesoderm: notochord and muscle. In this experiment, we will indicate where the dorsal mesoderm-inducing activity is localized in the very early gastrula, and what is an important event for specification of the dorsal axis mesoderm during gastrulation. Recombination experiments showed that dorsal mesoderm-inducing activity was localized definitively in the endodermal epithelium (EE) of the lower marginal zone, with a dorso-ventral gradient; and the EE itself differentiated into endodermal tissues, mainly pharyngeal endoderm. Nevertheless, when dorsal EE alone was transplanted into the ventral region, a secondary axis with dorsal mesoderm was barely formed. However, when dorsal EE was transplanted with the bottle cells which by themselves were incapable of mesoderm induction, a second axis with well-developed dorsal mesoderm was observed. When the animal half with the lower marginal zone was rotated 180° and recombined with the vegetal half, most of the rotated embryos formed only one dorsal axis at the primary blastopore side. The present results suggest that there are at least two essential processes in dorsal axis formation: mesoderm induction of the upper marginal zone by endodermal epithelium of the lower marginal zone, and dorsalization of the upper dorsal marginal zone evoked during involution.

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.…”

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

“…8 and 9). On grafting the LDMZ, a complete secondary axis is organized (Yamamoto and Suzuki, 1994;Imoh et al 1998), indicating that grafted LDMZ can induce an anteroposterior regional difference in inducing activity of the secondary induced notochord (Fig. 3E).…”

“…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).…”

“…Grafting experiments (Yamamoto and Suzuki, 1994) confirm the secondary axis organizing activity of the LDMZ, in which grafted LDMZ differentiates into endoderm but induces a complete secondary axis, and that the secondary axis-inducing Early gastrula (stage 11) DMZ is divided into three parts along the midline according to the presumptive fate of pharyngeal endoderm (A), trunk-tail notochord (C) and a mixture of pharyngeal endoderm, putative prechordal plate and most anterior part of the trunk notochord (B). Each part (0.3 Â 0.4 mm) is isolated and cultured alone (isolation culture) to examine self-differentiation, or its inducing activity is assayed by the sandwich assay method in which part A, B or C is wrapped between two sheets of animal cap ectoderm from stage 11 and cultured for 2 weeks.…”

Expression of a Novel Matrix Metalloproteinase Gene during Cynops Early Embryogenesis

“…Yamamoto and Suzuki (3) indicated that there were at least two essential processes in the dorsal mesoderm determination of the dorsal marginal zone during gastrulation: the dorsal mesoderm induction by the lower dorsal marginal zone and specification of the induced mesoderm during the involution movement. It was also suggested that cells capable of forming the notochord were located out of the fate map, but they could not differentiate into the dorsal mesoderm without some degree of involution (4).…”