I. PROBLEM OF THE ORGANIZER
9
and retained until the gastrula stage or later according to the embryonic
area. Yolk platelets during early developmental stages undergo
characteristic morphological changes which are closely related with the
progressive differentiation of the cells, and possibly with the organizer
action. The first change is visible in the superficial granular layer which
decreases in thickness and subsequently disappears completely. The
surface of the main body then assumes a fine laminar appearance. Later
the whole main body is converted into a membranous structure, in
which a concentric arrangement of membranes is often apparent.
Karasaki (1959a) points out the possibility that in this way cytoplasmic
membranous structures may be directly derived from the yolk platelets.
Lanzavecchia and Le Coultre (1958) studying similar laminar structures
formed from yolk platelets in i?ana-embryos believe that it is possible
to follow step by step the transformation of yolk platelets into mitochondria. It should be pointed out that the stage of alleged transformation of yolk platelets coincides approximately with the stage when a
quick rise in mitochondrial population occurs. However, biochemical
evidence is probably needed before the idea can be accepted.
The chemical nature of the particles of the superficial layer attracts
our attention especially in connection with the organizer phenomenon.
In electron micrographs the particles show a close similarity with the
fine particles which are scattered within the cytoplasm or attached to
the cytoplasmic vesicles and represent ribonucleoprotein particles.
Lanzavecchia and Le Coultre (1958) identify the superficial particles
of yolk platelets as ribonucleoprotein particles, and suggest that the
cytoplasm obtains a supply of ribonucleoprotein particles from yolk
platelets when the platelets lose their superficial layer. The idea appears
to agree well with the often made claim that the yolk fraction of the
amphibian embryo contains an appreciable amount of RNA (cf. Section
VIII). The same idea was current in 1957 in our laboratory, when it was
confirmed that the superficial layer shows basophilia. Not in complete
agreement with this idea was the fact that the diameter of the particles
(100 Á) was appreciably smaller than that of the cytoplasmic particles
of Palade type found in the same cell (150-200 Á). In a further cytochemical study conducted by K. Takata and Ono in our laboratory no
evidence was obtained for the presence of RNA in the superficial layer.
The toluidine blue staining of the layer was limited to the pH range
higher than 3, and was not affected by treatment with ribonuclease,
double treatment with deoxycholate followed by ribonuclease, double
treatment with pepsin or trypsin followed by ribonuclease, double
treatment with heat and ribonuclease, or treatment with hot TCA or
hot PCA. The ergastoplasm of Triturus pancreas cells treated simultaneously as the control on the same slides showed stainability also in
9
and retained until the gastrula stage or later according to the embryonic
area. Yolk platelets during early developmental stages undergo
characteristic morphological changes which are closely related with the
progressive differentiation of the cells, and possibly with the organizer
action. The first change is visible in the superficial granular layer which
decreases in thickness and subsequently disappears completely. The
surface of the main body then assumes a fine laminar appearance. Later
the whole main body is converted into a membranous structure, in
which a concentric arrangement of membranes is often apparent.
Karasaki (1959a) points out the possibility that in this way cytoplasmic
membranous structures may be directly derived from the yolk platelets.
Lanzavecchia and Le Coultre (1958) studying similar laminar structures
formed from yolk platelets in i?ana-embryos believe that it is possible
to follow step by step the transformation of yolk platelets into mitochondria. It should be pointed out that the stage of alleged transformation of yolk platelets coincides approximately with the stage when a
quick rise in mitochondrial population occurs. However, biochemical
evidence is probably needed before the idea can be accepted.
The chemical nature of the particles of the superficial layer attracts
our attention especially in connection with the organizer phenomenon.
In electron micrographs the particles show a close similarity with the
fine particles which are scattered within the cytoplasm or attached to
the cytoplasmic vesicles and represent ribonucleoprotein particles.
Lanzavecchia and Le Coultre (1958) identify the superficial particles
of yolk platelets as ribonucleoprotein particles, and suggest that the
cytoplasm obtains a supply of ribonucleoprotein particles from yolk
platelets when the platelets lose their superficial layer. The idea appears
to agree well with the often made claim that the yolk fraction of the
amphibian embryo contains an appreciable amount of RNA (cf. Section
VIII). The same idea was current in 1957 in our laboratory, when it was
confirmed that the superficial layer shows basophilia. Not in complete
agreement with this idea was the fact that the diameter of the particles
(100 Á) was appreciably smaller than that of the cytoplasmic particles
of Palade type found in the same cell (150-200 Á). In a further cytochemical study conducted by K. Takata and Ono in our laboratory no
evidence was obtained for the presence of RNA in the superficial layer.
The toluidine blue staining of the layer was limited to the pH range
higher than 3, and was not affected by treatment with ribonuclease,
double treatment with deoxycholate followed by ribonuclease, double
treatment with pepsin or trypsin followed by ribonuclease, double
treatment with heat and ribonuclease, or treatment with hot TCA or
hot PCA. The ergastoplasm of Triturus pancreas cells treated simultaneously as the control on the same slides showed stainability also in