116
ALBERTO MONROY AND RACHELE MAGGIO
somewhat from one species to another. Only the data pertaining to the
distribution of nucleic acids will be mentioned here.
In the newly fertilized egg of Paracentrotus
lividus (Pasteels et al.,
1958, 1959) the RNA appears to be bound to four different types of
structures: the vesicular
ergastoplasm
(hyaloplasmic region); the
annulated membranes (vitelline zone) (see Section V, C) ; the heavy bodies
(in the mitochondria region) which are intensely basophilic and whose
nature and relationship, if any, to the mitochondria, is unknown; and
finally, the fourth cell-structure containing RNA consists of some large
bodies and dense heavy bodies (Pasteels, 1958) the structure of which is
reminiscent of that of nucleoli (Afzelius, 1957).
These results have been confirmed by Immers (1960). However, his
conclusion that the RNA present in the heavy zone is in a 'denser form
with acid groups more available' does not seem to be sufficiently
substantiated. On the basis of observations on embryos stained with
pyronine and with the Hale reagent a difference between a Hale-positive
RNA present in the nuclei and a pyronine positive RNA present in the
cytoplasm has been claimed. The former is said to increase towards the
animal pole, whilst the latter accumulates at the vegetal pole (Markman,
1957). Whether the results of the histochemical tests employed justify
such a conclusion seems somewhat doubtful to the present writers.
Markman (1961a, c), using
14
C-adenine, found that its incorporation
in the nuclei of the animal region of the blastula was particularly
marked but that at the mesenchyme blastula stage, however, it was
reater in the nuclei of the vegetal region.
The significance of this distribution of RNA is unknown nor is
anything known of the changes in the RNA-containing structures in the
course of development.
By means of Feulgen staining it has been shown that DNA is present
as a thin crust just within the nuclear membrane (Burgos, 1955 ; Brächet
and Ficq, 1956) and the experiments with DNAase also confirm these
results (Agrell, 1958). It must be added that the estimation of DNA
content of nuclei of unfertilized sea urchin eggs isolated by a new
technique has given values essentially equal to those found in the sea
urchin sperm (Hinegardner, 1961). The question of the cytoplasmic
DNA reserve will be discussed later.
B. Biochemical Studies on Synthesis
1. DNA
It is a well-known fact that in the whole unfertilized sea urchin egg it
is difficult to make a quantitative estimate of DNA. The capacity to
synthesize DNA is acquired very soon after fertilization. Simmel and
ALBERTO MONROY AND RACHELE MAGGIO
somewhat from one species to another. Only the data pertaining to the
distribution of nucleic acids will be mentioned here.
In the newly fertilized egg of Paracentrotus
lividus (Pasteels et al.,
1958, 1959) the RNA appears to be bound to four different types of
structures: the vesicular
ergastoplasm
(hyaloplasmic region); the
annulated membranes (vitelline zone) (see Section V, C) ; the heavy bodies
(in the mitochondria region) which are intensely basophilic and whose
nature and relationship, if any, to the mitochondria, is unknown; and
finally, the fourth cell-structure containing RNA consists of some large
bodies and dense heavy bodies (Pasteels, 1958) the structure of which is
reminiscent of that of nucleoli (Afzelius, 1957).
These results have been confirmed by Immers (1960). However, his
conclusion that the RNA present in the heavy zone is in a 'denser form
with acid groups more available' does not seem to be sufficiently
substantiated. On the basis of observations on embryos stained with
pyronine and with the Hale reagent a difference between a Hale-positive
RNA present in the nuclei and a pyronine positive RNA present in the
cytoplasm has been claimed. The former is said to increase towards the
animal pole, whilst the latter accumulates at the vegetal pole (Markman,
1957). Whether the results of the histochemical tests employed justify
such a conclusion seems somewhat doubtful to the present writers.
Markman (1961a, c), using
14
C-adenine, found that its incorporation
in the nuclei of the animal region of the blastula was particularly
marked but that at the mesenchyme blastula stage, however, it was
reater in the nuclei of the vegetal region.
The significance of this distribution of RNA is unknown nor is
anything known of the changes in the RNA-containing structures in the
course of development.
By means of Feulgen staining it has been shown that DNA is present
as a thin crust just within the nuclear membrane (Burgos, 1955 ; Brächet
and Ficq, 1956) and the experiments with DNAase also confirm these
results (Agrell, 1958). It must be added that the estimation of DNA
content of nuclei of unfertilized sea urchin eggs isolated by a new
technique has given values essentially equal to those found in the sea
urchin sperm (Hinegardner, 1961). The question of the cytoplasmic
DNA reserve will be discussed later.
B. Biochemical Studies on Synthesis
1. DNA
It is a well-known fact that in the whole unfertilized sea urchin egg it
is difficult to make a quantitative estimate of DNA. The capacity to
synthesize DNA is acquired very soon after fertilization. Simmel and