2
TUNEO
YAMADA
organizer is to initiate directly or indirectly many of the differentiation
processes in other areas of the embryo (induction), and at the same time,
to initiate in its own area a number of differentiation processes leading
to formation of the essential part of the axial system of the embryo. The
effect of the organizer, from the standpoint of the area upon which it
acts, is to induce this area to switch from one type of differentiation to
another, but not to acquire the ability to differentiate. In spite of this
fact, since the type of differentiation induced by the organizer leads to
the formation of the central nervous system, the importance of the
organizer in vertebrate development is unquestionable.
Several years after the discovery of the organizer action by Spemann
and H. Mangold (1924), a vivid interest arose in the chemical nature of
the factor responsible for embryonic induction. Two prominent groups
of workers, the Cambridge group including J. Needham, Waddington
and others, and the Freiburg group including H. G. Fischer, Wehmeier,
H. Lehmann and others, conducted extensive research in the field.
Although the results were impressive and soon followed by the experiments of Barth, Suomalaien and Toivonen, Okada, and others, a
pessimistic atmosphere became prevalent, owing to the conviction that
what had been found by these researches seemed to be the activating
principle (evocator) which needs the organizing influence (individuation)
from the living embryo to bring about the formation of the secondary
embryonic axis.
In the forties, Brächet attacked the problem from a new angle, and
obtained results strongly supporting his view that RNA is the basic
factor in embryonic induction and differentiation. Meanwhile another
line of investigation, headed by Toivonen and Kuusi, attempting to
identify factors responsible for regional induction caused by adult
mammalian tissues was making its laborious beginning. In the last
decade, the ever increasing interest in cytochemical and biochemical
aspects of growth and differentiation, together with progress in biological
techniques, has given new impetus to the investigation into the problem
of embryonic induction.
Various new approaches are now being carried out, broadening the
scope of the problem and in the present articles some of these recent
advances will be discussed together with new data accumulated in our
laboratory. An attempt will be made to integrate the data obtained in
the various types of approach. Readers not acquainted with embryological aspects of the subject are referred to the following publications:
Weiss (1935); Spemann (1936); Lehmann (1945); Brächet (1947b, 1957);
Pasquini (1949); Needham (1950); Pasteéis (1951); Raven (1954);
Holtfreter and Hamburger (1955); Boyd (1955); Waddington (1956);
v. Woellwarth (1956); Dalcq (1957b).
TUNEO
YAMADA
organizer is to initiate directly or indirectly many of the differentiation
processes in other areas of the embryo (induction), and at the same time,
to initiate in its own area a number of differentiation processes leading
to formation of the essential part of the axial system of the embryo. The
effect of the organizer, from the standpoint of the area upon which it
acts, is to induce this area to switch from one type of differentiation to
another, but not to acquire the ability to differentiate. In spite of this
fact, since the type of differentiation induced by the organizer leads to
the formation of the central nervous system, the importance of the
organizer in vertebrate development is unquestionable.
Several years after the discovery of the organizer action by Spemann
and H. Mangold (1924), a vivid interest arose in the chemical nature of
the factor responsible for embryonic induction. Two prominent groups
of workers, the Cambridge group including J. Needham, Waddington
and others, and the Freiburg group including H. G. Fischer, Wehmeier,
H. Lehmann and others, conducted extensive research in the field.
Although the results were impressive and soon followed by the experiments of Barth, Suomalaien and Toivonen, Okada, and others, a
pessimistic atmosphere became prevalent, owing to the conviction that
what had been found by these researches seemed to be the activating
principle (evocator) which needs the organizing influence (individuation)
from the living embryo to bring about the formation of the secondary
embryonic axis.
In the forties, Brächet attacked the problem from a new angle, and
obtained results strongly supporting his view that RNA is the basic
factor in embryonic induction and differentiation. Meanwhile another
line of investigation, headed by Toivonen and Kuusi, attempting to
identify factors responsible for regional induction caused by adult
mammalian tissues was making its laborious beginning. In the last
decade, the ever increasing interest in cytochemical and biochemical
aspects of growth and differentiation, together with progress in biological
techniques, has given new impetus to the investigation into the problem
of embryonic induction.
Various new approaches are now being carried out, broadening the
scope of the problem and in the present articles some of these recent
advances will be discussed together with new data accumulated in our
laboratory. An attempt will be made to integrate the data obtained in
the various types of approach. Readers not acquainted with embryological aspects of the subject are referred to the following publications:
Weiss (1935); Spemann (1936); Lehmann (1945); Brächet (1947b, 1957);
Pasquini (1949); Needham (1950); Pasteéis (1951); Raven (1954);
Holtfreter and Hamburger (1955); Boyd (1955); Waddington (1956);
v. Woellwarth (1956); Dalcq (1957b).