Transmission of Homoiogenetic Induction in Presumptive Ectoderm of Newt Embryo

Abstract

J A P A N Using newt, Cyiiops pyrrliogaster., embryos, the production and/or transmission of a homoiogcnetic effect of the inddction within a presumptive ectoderm was investigated. The primary inductor was the swimbladder of a crucian carp, Caracius auratus. In the first experiment, a piece of presumptive ectoderm was isolated from an early gastrula and one-third of its inner surface was placed in contact with the swimbladder for 30 min. After removal of the inductor, the ectodermal piece was allowed to stand by itself for several hours (pre-cultivation), and then it was divided into three parts of equal size, i.e. the end that had been placed in contact with the swimbladder (PI), the next middle (P2) and the end part (P3).The tissues produced in each part were examined after 10 days' cultivation in Holtfreter's solution. The induction was evoked not only in PI, but also in P2 and P3 which had been free from the inductor. The incidences of tissue differentiation in P2 and P3 increased with the lapse of the pre-cultivation time, and the rise in P3 came after P2. These results suggested that the mesodermal tissues in the parts not placed in contact with the swimbladder (P2 and P3) were evoked by the homoiogenetic stimulus which came from PI and P2, respectively.In the next experiment, P2 of the ectodermal piece was substituted by an aged ectoderm which had lost its primary competence. In this system, the mesodermal induction was not evoked in P3. This suggested that the production of the homoiogenetic activity of the ectoderm might be associated with its cornpetenece.In the analysis of the primary induction system, the main line of research has been concerned with heterogenetic induction, in which the inductor (the archenteron roof) and the induced tissue (the neural plate) belong to different germ layers. However, besides the heterogenetic nature of primary induction, its homoiogenetic or assimilatory aspect can be seen in the pioneering work on primary induction by SPEMANN and MANGOLD (I). The secondary primodium consisted partly of the light tissue of the organizer (Triton cristatus) and partly of the pigmented materials of the host (T. tcreniatus). The homoiogenetic nature of this induction was clearly established by the discovery of neural induction by the neural tissue (2). Recently, an analytical approach to homoiogenetic induction was made by DEUCHAR (3). She made a combination experiment on a small number of induced cells (labelled with 3H-TdR) with a much larger number of uninduced cells (unlabelled) of Xenopus embryo, and she discovered that the participation of the uninduced cells in the formation of neural tissues in the induced cells had taken place in her system. The same was demonstrated by RASILO and LEIKOLA (4) with a quailchick system.

Coordinated induction of cell proliferation and syndecan expression in dental mesenchyme by epithelium: Evidence for diffusible signals

“…Alternatively, the epithelial signals may induce the mesenchymal cells to express the same or other signalling molecules, which subsequently induce syndecan expression in mesenchymal cells. In this case the induction would be mediated via homoiogenetic mechanism (Mangold and Spemann, 1927;Kurihara and Sasaki, 1981;Ruis i Altaba, 1990;Servetnick and Grainger, 1991). The possibility that syndecan, which is expressed early on in the dental epithelium, would act as a signal molecule inducing its own expression has been mostly ruled out (Vainio et al, 1989a).…”

Homoiogenetic Neural Inducing Activity of the Presumptive Neural Plate of Xenopus Laevis

“…The results of these earlier papers suggest that the sharp borders of the neural plate adjacent to the presumptive epidermis correlates to a mediollateral decline of the inducing activity of the chordamesoderm, spreading of homoiogenetic induction within the ectoderm and the loss of competence of the lateral ectodermal cells at the middle to the late neurula stage (1,19). Homoiogenetic induction was also observed in mesoderm formation using newts or chicken (7,12,13).…”