CHAPTER
I
A CHEMICAL APPROACH TO THE
PROBLEM OF THE ORGANIZER
TUNEO YAMADA
I. Introduction
1
II. Fine Structure of Embryonic Cells as Revealed by Electron Micrographs
3
A.
Mitochondria
3
B.
Ribonucleoprotein Particles and Cytoplasmic Vesicles
7
C.
Golgi Complex
8
D.
Yolk Platelets
8
E.
Pigment Granules
10
F.
Lipochondria
11
G.
Cell Membrane
11
H.
Nucleus
11
I.
Summary
12
III. Dorsalization by Subcytolytic Treatments
12
IV. Chemical Factors Operative in Heterogenous Induction
17
V. Inducing Ability of Fresh Samples of Subcellular Components of Amphibian
Embryos
27
VI. RNA and Specific Induction
34
VII. Transmission of Mediating Factors
38
VIII. Significance of Some Biochemical Events
45
IX. Concluding Remarks
47
References
50
I. Introduction
If a vertebrate at the end of its development is represented as a spatial
pattern composed of a number of discrete parts, differentiation is the
process by which each part is produced out of unspecialized cells which
together make up the embryo at an early stage of development. In the
later phase of development, various differentiation processes distinct
from each other are occurring simultaneously in separate groups of cells
within an embryo. The embryonic organization, i.e. the allocation of
differentiation processes to various areas of the embryo, is laid down in
its general feature by the polarity of the egg cell or by an interplay of
factors derived from the egg cell polarity, sometime after fertilization.
However, realization of the plan of organization is dependent upon a
multitude of epigenetic events occurring in later stages. The action of
'the organizer' is the most important of these events. A series of welldesigned surgical experiments demonstrated that the function of the
1