Head and trunk-tail organizing effects of the gastrula ectoderm of Cynops pyrrhogaster after treatment with activin A

Abstract

Differentiation tendency and the inducing ability of the presumptive ectoderm of newt early gastrulae were examined after treatment with activin A at a high concentration (100 ng/ml). The activin-treated ectoderm differentiated preferentially into yolk-rich endodermal cells. Combination explants consisting of three pieces of activin-treated ectoderm formed neural tissues and axial mesoderm along with endodermal cells. However, the neural tissue was poorly organized and never showed any central nervous system characteristics. When the activin-treated ectoderm was sandwiched between two sheets of untreated ectoderm, the sandwich explants differentiated into trunk-tail or head structures depending on the duration of preculture of activin-treated ectoderm in Holtfreter's solution. Short-term (0-5 h) precultured ectoderm induced trunk-tail structures accompanied by axial organs, alimentary canal and beating heart. The arrangement of the explant tissues and organs was similar to that of normal embryos. However, archencephalic structures, such as forebrain and eye, were lacking or deficient. On the other hand, long-term (10-25 h) precultured ectoderm induced archencephalic structures in addition to axial organs. Lineage analysis of the sandwich explants using fluorescent dyes revealed that the activin-treated ectoderm mainly differentiated into endodermal cells and induced axial mesoderm and central nervous system in the untreated ectoderm. These results suggest that activin A is one of the substances involved in triggering endodermal differentiation and that the presumptive ectoderm induced to form endoderm displays "trunk-tail organizer" or "head organizer" effects, depending on the duration of preculture.

In vitro organogenesis from undifferentiated cells in Xenopus

“…Importantly, the induced structure was determined by the length of exposure to activin. When an animal cap that had been incubated with activin A for 12 hr was sandwiched, a trunk-tail structure was induced, whereas incubation with activin A for 24 hr caused the sandwiched explants to differentiate into a head structure (Ariizumi and Asashima, 1995). These results are very interesting in that they mirror the outcomes of a classic experiment, in which transplantation of a dorsal rip at the early gastrula stage into the ventral region of another gastrula induced a head-like structure, while transplantation of a dorsal tip at the late gastrula stage induced a trunktail (Spemann, 1931).…”

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

“…In newt (Cynops pyrrhogaster), presumptive ectoderm treated with a high concentration of activin A mainly differentiates into yolk-rich endodermal cells; different from Xenopus (Ariizumi & Asashima 1995;Ninomiya et al 1998). Cynops activintreated ectoderm induces trunk-tail structures (including axial mesoderm) or head structures when sandwiched between two sheets of ectoderm in a time-dependent manner after treatment with activin A (Ariizumi & Asashima 1995). In addition, Cynops activin-treated ectoderm induces a whole secondary axis (from head to tail) when transplanted into the VMZ of blastulae .…”

Changes in the adhesive properties of dissociated and reaggregated Xenopus laevis embryo cells

“…These phenomena were also observed in experiments in which presumptive foregut was used instead of activin-treated ectoderm. These findings show that activin-treated ectoderm undergoes changes in adhesive properties and can act as the single organizing center in Cynops (Ariizumi & Asashima 1995;Ninomiya et al 1998). In addition, when presumptive epidermal explants from pigmented neurula embryos and neural plate explants from unpigmented neurula embryos were dissociated and mixed, the cells reaggregated such that epidermal cells covered other cell types (Townes & Holtfreter 1955).…”