1 5 . E M B R Y O G E N E S I S in
vitro
549
categories of substances: proteins and ribonucleic acids. Many authors
have shown that preparations rich in ribonucleoproteins (Brachet,
Toivonen, Yamada and Takata, Hayashi, etc.) are powerful inducers,
mainly of the archencephalon. The pertinent question was whether
ribonucleoproteins act through their R N A or through the associated
protein. The same authors subsequently showed that these preparations, treated with ribonuclease, do not lose their inducing power—an
observation which directed research towards the idea of the active role
of a protein.
Moreover, Toivonen (1950), Yamada (1950b), Kuusi (1953) showed
that certain protein fractions of active extracts or of purified proteins,
such as muscle proteins, have intense specific inducing action.
Three groups of embryologists have particularly studied the chemical
nature of specific inducers; the Toivonen school in Finland, the
Yamada group in Japan, and the Tiedemanns in Germany. These
authors have concentrated on specific inducers such as guinea-pig
kidney and liver, and guinea-pig bone marrow, or on purified fractions
of complex inducers such as the embryo juice of the chick.
The results can be grouped into three distinct categories:
1. Effect of Temperature
and of Chemical
Reagents
The initial researches of Holtfreter (1934) and of Chuang (1938) had
shown that progressive heating of heterogeneous inducers modifies the
type of differentiation which is induced before it completely annuls
their effect. Toivonen (1950, 1953a, b , 1954), Yamada and Takata
(1955), and Yamada (1959) have shown that specific inducers of the
spinal cord, of the deuterencephalon, and of the mesoderm are inactivated by heat. Their properties become progressively transformed
from the initial type into the archencephalic type. It is noteworthy
to consider that guinea-pig bone marrow treated in the vapour of
boiling water for periods varying from 25 to 150 sec, goes successively
from the mesodermal to the archencephalic type of inducer, and passes
through spino-caudal and deuterencephalic stages (Yamada, 1959).
These modifications of inducing properties correspond precisely to the
different types of inductions effected by the natural inducer in the
course of its migration from the back to the front of the archenteric
roof (Fig. 10).
In all these experiments the archencephalic inducer is the one most
resistant to heat; when it loses its capacity to induce an anterior brain,
it is still capable of inducing sense organs and crystalline lenses, and,
at the last resort, it can induce pigmented epidermal vesicles, melanophores, and mesenchyme. Yamada (1950a) interprets these results as
confirmatory of the existence of a dorso-ventral gradient of the inducing
vitro
549
categories of substances: proteins and ribonucleic acids. Many authors
have shown that preparations rich in ribonucleoproteins (Brachet,
Toivonen, Yamada and Takata, Hayashi, etc.) are powerful inducers,
mainly of the archencephalon. The pertinent question was whether
ribonucleoproteins act through their R N A or through the associated
protein. The same authors subsequently showed that these preparations, treated with ribonuclease, do not lose their inducing power—an
observation which directed research towards the idea of the active role
of a protein.
Moreover, Toivonen (1950), Yamada (1950b), Kuusi (1953) showed
that certain protein fractions of active extracts or of purified proteins,
such as muscle proteins, have intense specific inducing action.
Three groups of embryologists have particularly studied the chemical
nature of specific inducers; the Toivonen school in Finland, the
Yamada group in Japan, and the Tiedemanns in Germany. These
authors have concentrated on specific inducers such as guinea-pig
kidney and liver, and guinea-pig bone marrow, or on purified fractions
of complex inducers such as the embryo juice of the chick.
The results can be grouped into three distinct categories:
1. Effect of Temperature
and of Chemical
Reagents
The initial researches of Holtfreter (1934) and of Chuang (1938) had
shown that progressive heating of heterogeneous inducers modifies the
type of differentiation which is induced before it completely annuls
their effect. Toivonen (1950, 1953a, b , 1954), Yamada and Takata
(1955), and Yamada (1959) have shown that specific inducers of the
spinal cord, of the deuterencephalon, and of the mesoderm are inactivated by heat. Their properties become progressively transformed
from the initial type into the archencephalic type. It is noteworthy
to consider that guinea-pig bone marrow treated in the vapour of
boiling water for periods varying from 25 to 150 sec, goes successively
from the mesodermal to the archencephalic type of inducer, and passes
through spino-caudal and deuterencephalic stages (Yamada, 1959).
These modifications of inducing properties correspond precisely to the
different types of inductions effected by the natural inducer in the
course of its migration from the back to the front of the archenteric
roof (Fig. 10).
In all these experiments the archencephalic inducer is the one most
resistant to heat; when it loses its capacity to induce an anterior brain,
it is still capable of inducing sense organs and crystalline lenses, and,
at the last resort, it can induce pigmented epidermal vesicles, melanophores, and mesenchyme. Yamada (1950a) interprets these results as
confirmatory of the existence of a dorso-ventral gradient of the inducing