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 ROLE OF REGIONAL SPECIFIC
INDUCERS IN THE PRIMARY DETERMINATION
AND DIFFERENTIATION OF AMPHIBIA*

H. TIEDEMANN

Heiligenberg-Institut Abt. Mangold, Heiligenberg/Bodensee,
Western Germany


SUMMARY

Two regional specific inducing factors can be isolated from chick embryos. The 'mesodermal" factor is protein in nature and stimulates the competent ectoderm. of amphibian gastrulae to form muscle, notochord and pronephros. The "neural" factor induces archencephalic structures. Complex hind-head and tail inductions are very probably formed by a co-operation of the two factors. Both factors are inactivated by trypsin and pepsin. The mesodermal factor is more easily inactivated by heating or incubation with thioglycolic acid.

The factors are only starting reaction chains. Further differentiation largely depends on the activation of genes in the reacting tissue. In this respect experiments concerning activation of nuclear RNA synthesis during gastrulation and neurulation and inhibition of differentiation by structural analogs of pyrimidines and pyrimidine nucleosides are discussed.


INTRODUCTION

An organism originates from the fertilized egg with a wide variety of forms and functions. Developmental biology investigates the factors and conditions which bring about such a complex differentiation. At an early period of research the question was already under discussion whether the determining factors of development are situated in the cell nucleus or in the cytoplasm. One of the first fruitful hypotheses of development is August Weismann ( 1885) "Germ-Plasm-Theory". It starts from the assumption that even the very first cell divisions are hereditarily unequal. Beginning at the first steps of development the nuclei of all cells, except the germ cells, would lose part of their "determinants", which, in our modern terminology, correspond to the genes. Each "organanlage" would be determined by a fixed germ area.

____________________
*
Dedicated to the memory of Professor Dr. Otto Mangold on whose initiative our investigations reported in this paper were begun in 1954.

Abbreviations: DOC = deoxycholate, RNA = ribonucleic acid, DNA = deoxyribonucleic acid, DEAE = diethylaminoethyl-, CM = carboxymethyl-.

-183-

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