EARLY DEVELOPMENT OF THE SEA URCHIN
139
blastula stage followed by a recovery beginning at the mesenchyme
blastula stage (Monroy et al., 1951). This decrease was not observed in
cases of abnormal development. Which pigment is responsible for the
quantitative change is obscure. From the fractionation data of De
Nicola and Goodwin (1954) it appears that the only one which undergoes
a significant decrease from fertilization to the blastula stage, followed by
an increase, is the one named A6 (probably a hydroxy derivative of the
echinenone).
Even less is known about the echinochrome that constitutes the major
pigment of the eggs of the genus Arbacia but is present also in the cells
of the body fluid (eleocytes) of all sea urchins. Traces of echinochrome
are present in the eggs of Paracentrotus but the pigment begins to appear
in measurable amounts together with the first appearance of the
eleocytes and microscopic inspection of the embryos after removal of the
carotenoids shows that it is present in the body of these cells (Monroy
etal, 1951).
As this brief account has shown, our knowledge of the significance of
the pigment is almost non-existent and it would be extremely interesting
to find out if and how it participates in the differentiation of the sea
urchin embryo.
VI. Conclusions
From the foregoing it should be clear that, in spite of the amount of
work done, we are still far from being able to form a co-ordinated picture
of most of the biochemical events in sea urchin development.
As a first approximation, the respiratory curve may be regarded as an
overall description of the major features of sea urchin development. The
first part of the curve, the so-called exponential part, is dominated by
the rapid succession of cell cleavages, by intense DNA synthesis, by a
first wave of protein synthesis which has been suggested as being of
importance for the differentiation of the vegetal structures of the
embryo and, a little later, by the beginning of RNA metabolism.
The main event underlying the early stages of development is the
activation of the biochemical systems involved in DNA and protein
synthesis. Whether the activation process is brought about by one single
or by multiple events is as yet obscure. In the case of the ribosomes, the
evidence quoted (Hultin and Bergstrand, 1960; Hultin, 1961) indicates
a structural rearrangement, whereas in other cases, such as the protein
synthesizing ability of the mitochondria (Giudice, 1960), the amino-acid
activating enzymes (Scarano and Maggio, 1957), the enzymes of
nucleotide metabolism (Scarano and Maggio, 1959b) and others, there is
a suggestion of the release of some inhibitor (Maggio and Monroy, 1959).
139
blastula stage followed by a recovery beginning at the mesenchyme
blastula stage (Monroy et al., 1951). This decrease was not observed in
cases of abnormal development. Which pigment is responsible for the
quantitative change is obscure. From the fractionation data of De
Nicola and Goodwin (1954) it appears that the only one which undergoes
a significant decrease from fertilization to the blastula stage, followed by
an increase, is the one named A6 (probably a hydroxy derivative of the
echinenone).
Even less is known about the echinochrome that constitutes the major
pigment of the eggs of the genus Arbacia but is present also in the cells
of the body fluid (eleocytes) of all sea urchins. Traces of echinochrome
are present in the eggs of Paracentrotus but the pigment begins to appear
in measurable amounts together with the first appearance of the
eleocytes and microscopic inspection of the embryos after removal of the
carotenoids shows that it is present in the body of these cells (Monroy
etal, 1951).
As this brief account has shown, our knowledge of the significance of
the pigment is almost non-existent and it would be extremely interesting
to find out if and how it participates in the differentiation of the sea
urchin embryo.
VI. Conclusions
From the foregoing it should be clear that, in spite of the amount of
work done, we are still far from being able to form a co-ordinated picture
of most of the biochemical events in sea urchin development.
As a first approximation, the respiratory curve may be regarded as an
overall description of the major features of sea urchin development. The
first part of the curve, the so-called exponential part, is dominated by
the rapid succession of cell cleavages, by intense DNA synthesis, by a
first wave of protein synthesis which has been suggested as being of
importance for the differentiation of the vegetal structures of the
embryo and, a little later, by the beginning of RNA metabolism.
The main event underlying the early stages of development is the
activation of the biochemical systems involved in DNA and protein
synthesis. Whether the activation process is brought about by one single
or by multiple events is as yet obscure. In the case of the ribosomes, the
evidence quoted (Hultin and Bergstrand, 1960; Hultin, 1961) indicates
a structural rearrangement, whereas in other cases, such as the protein
synthesizing ability of the mitochondria (Giudice, 1960), the amino-acid
activating enzymes (Scarano and Maggio, 1957), the enzymes of
nucleotide metabolism (Scarano and Maggio, 1959b) and others, there is
a suggestion of the release of some inhibitor (Maggio and Monroy, 1959).