I. PROBLEM
OF THE
ORGANIZER
39
molecule occupying the cell surface attracts one particular molecular
species from the cell interior, and thereby changes the array of free
molecules of the cell. However, it is easier to imagine that the protein
molecule passes into the cell interior and there influences the differentiation process of the cell. The passage must occur without preceding
degradation of protein, since denaturating treatments of the protein
may either abolish specificity of induction or inactivate it altogether.
Although passage of protein across the cell membrane is contrary to the
classical theory of cell permeability, an increasing body of evidence
speaks for its occurrence. To cite a few of examples, Leduc, Coons, and
Connolly (1955) demonstrated by the use of fluorescent antibodies the
presence of antigens in the cytoplasm of the cells lining the sinuses of
the lymph nodes, after injection of antigens. By injecting serum
albumin, and serum globulin doubly labelled with
3 5
S, and
1 3 1
I
Haurowitz and his collaborators (Walter et al., 1957) obtained evidence
for intact uptake of protein in the cell of liver, spleen, etc. Further,
according to Straus (1957) horse-radish peroxidase injected in rats can
be detected preferentially localized in the 'droplet fraction' of the
kidney cells. For further evidence, readers are referred to reviews of
Harris (1958), Ebert (1955), and Schechtmann (1956). That the embryonic cells of amphibia are able to take up protein from the ambient
medium is suggested by the experiment of Brächet and Ledoux (1955)
in which cleaving frog eggs immersed in a ribonuclease solution showed
blockage of cell-division due to abnormalities of the achromatic
apparatus which contains RNA. However, in later stages, penetration
of the enzyme is apparently hindered by development of a thicker
surface coat.
The most probable mechanism of the uptake of intact protein by the
embryonic cell in induction experiments may be that of pinocytosis.
First found by Lewis (1931) in tissue culture cells, pinocytosis is now
known to occur in a variety of cell types (Mast and Doyle, 1934; Gey et
al., 1954; Holter and Marshall, 1954; Schumaker, 1958). Pinocytosis is
based on invagination of the cell membrane, which leads to formation of
a small vesicle or canal which pinches off from the cell membrane, and
migrates inward. That similar invaginations can occur in the submicroscopic dimension is shown by many electron microscopic studies of tissue
cells, in which corresponding pictures are witnessed, and interpreted in
the same sense (Palade, 1953; Dempsey, 1953). Bennett (1956) incorporated this phenomenon into the general idea of membrane flow and
membrane vesiculation, in which all types of membranous structures of
the cell are conceived to be in a dynamic interrelation.
These considerations suggest that in the induction experiment using
the nylon technique (Section IV), protein dissolved in the medium may
OF THE
ORGANIZER
39
molecule occupying the cell surface attracts one particular molecular
species from the cell interior, and thereby changes the array of free
molecules of the cell. However, it is easier to imagine that the protein
molecule passes into the cell interior and there influences the differentiation process of the cell. The passage must occur without preceding
degradation of protein, since denaturating treatments of the protein
may either abolish specificity of induction or inactivate it altogether.
Although passage of protein across the cell membrane is contrary to the
classical theory of cell permeability, an increasing body of evidence
speaks for its occurrence. To cite a few of examples, Leduc, Coons, and
Connolly (1955) demonstrated by the use of fluorescent antibodies the
presence of antigens in the cytoplasm of the cells lining the sinuses of
the lymph nodes, after injection of antigens. By injecting serum
albumin, and serum globulin doubly labelled with
3 5
S, and
1 3 1
I
Haurowitz and his collaborators (Walter et al., 1957) obtained evidence
for intact uptake of protein in the cell of liver, spleen, etc. Further,
according to Straus (1957) horse-radish peroxidase injected in rats can
be detected preferentially localized in the 'droplet fraction' of the
kidney cells. For further evidence, readers are referred to reviews of
Harris (1958), Ebert (1955), and Schechtmann (1956). That the embryonic cells of amphibia are able to take up protein from the ambient
medium is suggested by the experiment of Brächet and Ledoux (1955)
in which cleaving frog eggs immersed in a ribonuclease solution showed
blockage of cell-division due to abnormalities of the achromatic
apparatus which contains RNA. However, in later stages, penetration
of the enzyme is apparently hindered by development of a thicker
surface coat.
The most probable mechanism of the uptake of intact protein by the
embryonic cell in induction experiments may be that of pinocytosis.
First found by Lewis (1931) in tissue culture cells, pinocytosis is now
known to occur in a variety of cell types (Mast and Doyle, 1934; Gey et
al., 1954; Holter and Marshall, 1954; Schumaker, 1958). Pinocytosis is
based on invagination of the cell membrane, which leads to formation of
a small vesicle or canal which pinches off from the cell membrane, and
migrates inward. That similar invaginations can occur in the submicroscopic dimension is shown by many electron microscopic studies of tissue
cells, in which corresponding pictures are witnessed, and interpreted in
the same sense (Palade, 1953; Dempsey, 1953). Bennett (1956) incorporated this phenomenon into the general idea of membrane flow and
membrane vesiculation, in which all types of membranous structures of
the cell are conceived to be in a dynamic interrelation.
These considerations suggest that in the induction experiment using
the nylon technique (Section IV), protein dissolved in the medium may