Differentiation of Partially Mesodermalized Ectoderm; Homoiogenetic and Heterogenetic Induction by Primarily Induced Part of the Ectoderm

Abstract

Using embryos of the Japanese newt, Cynops pyrrhogaster, homoiogenetic and heterogenetic induction were investigated in the partially mesodermalized presumptive ectoderm. Half of the isolated presumptive ectoderm was placed in contact with the swimbladder of the crucian carp, Carasius auratus: for 15 or 60 min, while the other half was stained with Nile blue sulfate at the same time. The distribution of the stained cells in the tissues evoked in the explants was examined after cultivation for 10 days.This indicates homoiogenetic induction by the primarily induced part of the ectoderm on the other half. The neural and epidermal tissues in the explants were composed of stained cells only, except in one case. We conclude that the neural tissues.are derived from cells not placed in contact with the swimbladder and that they are induced by the primarily induced part of the ectoderm.Some mesodermal tissues were composed of both stained and unstained cells.The idea of "homoiogenetic induction" was originally proposed by MANGOLD and SPEMANN (8) with regard to neural induction, and many papers on the homoiogenetic nature of neural induction have been published (1, 5, 6, 7, 10,19,22). As for mesodermal induction, the homoiogenetic nature was demonstrated by implantation and explantation experiments (3, 1 1, 13, 16, 17). Since homoiogenetic or assimilatory induction may be caused by cell to cell transmission of an inducing stimulus (15), the analysis of this transmission as well as that of layer to layer (14, 20) may offer an useful key for understanding primary induction.Recently, KAWAKAMI (2) demonstrated the strong mesodermal inducing activity of the swimbladder of the crucian carp. Since the area of contact between the isolated presumptive ectoderm and the swimbladder can be manually controlled due to their sheet-like form, the swimbladder is a useful tool for the analysis of propagation of the inducing stimulus within a reactor.In the present study, half of the isolated presumptive ectoderm of newt gastrula was placed in contact with the swimbladder and at the same time, the other half was stained with Nile blue sulfate to distinguish both parts in one explant. MATERIALS AND METHODSEmbryos of the Japanese newt, Cynops pyrrhogaster, were used for all experiments. The presumptive ectoderm of an early gastrula (stage 12a (9)) was isolated manually ( 1 . 0~ 1.5 mm in size) and used as the reactor.

Neural-inducing activity of newly mesodermalized ectoderm

“…The mesodermalized ectoderm was found to be capable of inducing neural structures in the combined ectoderm. It has already been shown by Grunz (1979) and Nishijima et al (1978) that the induction of neural structures occurs secondarily between non-induced ectoderm and mesodermalized cells in an ectoderm explant treated with vegetalizing factors. The present results further indicate that neural structures are induced even in 18 h ectoderm combined with mesoderrealized ectoderm.…”

Transmission of Homoiogenetic Induction in Presumptive Ectoderm of Newt Embryo

“…Using guinea pig bone marrow and siwmbladder as the inductor, the present authors have tried to demonstrate the homoiogenetic nature of mesodermal induction (5,6). In this report, the authors attempt to demonstrate the propagation of the inducing stimulus within a germ layer, because the stimulus of homoiogenetic induction, in contrast to heterogenetic induction, would propagate within a germ layer as suggested by RAVEN'S experiment (7).…”