Biological Organization at the Cellular and Supercellular Level: A Symposium Held at Varenna, 24-27 September, 1962, under the Auspices of UNESCO

By R. J. C. Harris | Go to book overview

THE TRANSMISSION OF INFORMATION
DURING PRIMARY EMBRYONIC INDUCTION

L. SAXÉN

University of Helsinki, Helsinki, Finland


SUMMARY

This paper contains a discussion of some recent results obtained with respect to the transmission of inductive information and detectable material from the inductor to the responding ectoderm during primary induction. It may be concluded that the inductive stimulus is capable of operating over a certain distance without cytoplasmic contact. The mechanism of this transmission is unknown, but the findings from various experiments have shown that a transfer of materials from the inductor to the ectoderm does occur during the process of induction. The transmission of inductive information is time-dependent, and this is due, at least in part, to delayed release of the active compounds from the inductor tissue. On the other hand, the reactivity of the responding tissue changes with time, and the type of differentiation initiated by an inductive stimulus is dependent upon the time of its application.

Thus different factors have always to be considered when the results obtained from such induction experiments are being interpreted: the amount and the quality of different active components, their release by the inductor tissue, and finally the selective changes in the competence of the responding ectodermal cells.


INTRODUCTION

The basic question in the problem of primary embryonic induction is how a cell population of an obvious genetic homogenicity is affected by environmental factors in such a way that it becomes differentiated in various directions. In other words, we are facing the problems posed by the epigenetic factors brought into being by the changes in expression of the genetic potentialities of a given cell population. A number of different theories have recently been discussed in this connection, including suggestions on gene activation, enzyme induction and certain repressor mechanisms ( Yamada, 1962; Toivonenet al., 1961; Tiedemann et al., 1961). However, experimental results have not provided conclusive evidence for these and similar hypotheses. The material and the experimental set-ups utilized by scientists studying the problem of primary induction do not seem to be suitable for any direct approach to

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