44
TUNEO
YAMADA
membrane vesiculation; (iii) discharge and uptake, by a mechanism
other than membrane vesiculation.
In the chick embryo pertinent data have been obtained by Bellairs
(1959): during the period of primary induction a distinct layer of
intercellular matrix of ca. 200 Á or more separated the cell membranes
of the lowest cell of the ectoderm and of the uppermost cell of the
mesoderm. Particles are present in the matrix, which resemble the
Palade granules. Although not mentioned in her text, several small
cytoplasmic vesicles are shown in the micrographs not far from the cell
membranes of an ectoderm cell facing a mesoderm cell. Perhaps what
has been suggested for the amphibian in (ii) and (iii) above may be
applicable to the chick embryo.
Some attempts have been made to follow the possible passage of the
inducing agent by the use of tracers. Ficq (1954) marked the amphibian
organizer with glycine- 114
C and orotic acid-214
C and either implanted
it into the blastocoel or fused it with isolated presumptive ectoderm
according to the sandwich technique. In the induced structures as well
as in the primary axial structures radioactivity was indicated by
ß-track autoradiography. She found in the data support for Brachet's
idea of the transfer of cytoplasmic granules. In a similar experiment of
Sirlin, Brahma, and Waddington (1956), in which the organizer was
cultured in glycine14
C, methionine35
S, or adenine-814
C and was
inserted into the blastocoel or in sandwiches, higher radioactivity was
detected in the induced neural structures by the stripping film autoradiography. Most of the activity was in the nuclei. They suggested that
the observed passage of the tracer occurred in the form of small
molecules and was not connected with the alleged transfer of inducing
agents. Pantelouris and Mulherkar (1957) made a comparable experiment in the chick using methionine35
S to mark the organizer. A
considerable transfer found in the induced neural tube was interpreted
to be mainly due to diffusion in the form of amino acid, because dilution
with unlabelled methionine suppressed the transfer of radioactivity
considerably, and further the host neural tube adjacent to the implant
showed a high activity. Waddington and Mulherkar (1957) compared
the intracellular distribution of radioactivity of the last case with that
of the experiment in which the chick embryo was simply cultured in
methionine35
S. In the latter case the activity was found mainly localized
in the nuclei as it was in the earlier similar case studied by Sirlin and
Waddington (1954), while in the former case a considerable amount of
activity was present also in the cytoplasm. On the ground of the
difference in localization Waddington and Mulherkar argued that from
the labelled organizer some substance which is more complex than free
amino acid, and carries
3 5
S atoms, might be transferred to the host cells.
TUNEO
YAMADA
membrane vesiculation; (iii) discharge and uptake, by a mechanism
other than membrane vesiculation.
In the chick embryo pertinent data have been obtained by Bellairs
(1959): during the period of primary induction a distinct layer of
intercellular matrix of ca. 200 Á or more separated the cell membranes
of the lowest cell of the ectoderm and of the uppermost cell of the
mesoderm. Particles are present in the matrix, which resemble the
Palade granules. Although not mentioned in her text, several small
cytoplasmic vesicles are shown in the micrographs not far from the cell
membranes of an ectoderm cell facing a mesoderm cell. Perhaps what
has been suggested for the amphibian in (ii) and (iii) above may be
applicable to the chick embryo.
Some attempts have been made to follow the possible passage of the
inducing agent by the use of tracers. Ficq (1954) marked the amphibian
organizer with glycine- 114
C and orotic acid-214
C and either implanted
it into the blastocoel or fused it with isolated presumptive ectoderm
according to the sandwich technique. In the induced structures as well
as in the primary axial structures radioactivity was indicated by
ß-track autoradiography. She found in the data support for Brachet's
idea of the transfer of cytoplasmic granules. In a similar experiment of
Sirlin, Brahma, and Waddington (1956), in which the organizer was
cultured in glycine14
C, methionine35
S, or adenine-814
C and was
inserted into the blastocoel or in sandwiches, higher radioactivity was
detected in the induced neural structures by the stripping film autoradiography. Most of the activity was in the nuclei. They suggested that
the observed passage of the tracer occurred in the form of small
molecules and was not connected with the alleged transfer of inducing
agents. Pantelouris and Mulherkar (1957) made a comparable experiment in the chick using methionine35
S to mark the organizer. A
considerable transfer found in the induced neural tube was interpreted
to be mainly due to diffusion in the form of amino acid, because dilution
with unlabelled methionine suppressed the transfer of radioactivity
considerably, and further the host neural tube adjacent to the implant
showed a high activity. Waddington and Mulherkar (1957) compared
the intracellular distribution of radioactivity of the last case with that
of the experiment in which the chick embryo was simply cultured in
methionine35
S. In the latter case the activity was found mainly localized
in the nuclei as it was in the earlier similar case studied by Sirlin and
Waddington (1954), while in the former case a considerable amount of
activity was present also in the cytoplasm. On the ground of the
difference in localization Waddington and Mulherkar argued that from
the labelled organizer some substance which is more complex than free
amino acid, and carries
3 5
S atoms, might be transferred to the host cells.