100
ALBERTO MONROY AND RACHELE MAGGIO
distribution of the mitochondria (as judged by the above criteria) is
almost equal to that found in the unfertilized eggs.
A further point to be taken into consideration is that the rationale
behind the technique of homogenization and preparation of cell
components by differential centrifugation is the assumption that all the
cells of the system under consideration are endowed with the same
properties. In the case of the embryo this is evidently a gratuitous
assumption and indeed a quite erroneous one. It may just be mentioned
here that in the mesenchyme blastula the uptake of labelled amino-acids
is considerably lower in the cells of the primary mesenchyme and in the
entire vegetative territory than in the rest of the larva (Bosco and
Monroy, 1962).
III. Protein Synthesis During the Early Development
of the Sea Urchin
A. General Metabolic Background
The general metabolic background of the development of the sea
urchin egg is best outlined by the well-known S-shaped respiratory
curve (Lindahl, 1939 ; Borei, 1948). A first period of exponential increase
from fertilization to the early blastula is followed by a plateau extending
somewhat beyond the hatching of the embryo and then by a second
period of quite steep increase in oxygen consumption beginning a little
before the appearance of the primary mesenchyme. The shape of the
curve indicating the rate of increase of the cell population (Köhler, 1912 ;
Zeuthen, 1953) duplicates that of oxygen consumption (Fig. 1). In a
series of papers Zeuthen (summarized in 1953) has given evidence of a
respiratory rhythm accompanying cell division and indeed of increasing
rates of respiration at the stages where nuclei reappear and persist.
According to this author the decisive factor in the exponential increase
of respiration during cleavage is the increasing ratio of 'whole' (i.e.,
surrounded by a membrane) to 'open' nuclei which holds good till about
the 10th cleavage. At this point cleavages and increase of respiration
both come to a standstill and then resume again at the late blastula
stage. Zeuthen (1953) has also drawn attention to the coincidence
between the phases of respiratory increase during the mitotic cycle and
DNA synthesis.
Recently Immers and Runnström (1960) observed that treatment of
the eggs with 2 : 4 dinitrophenol during the period of exponential
respiratory increase brings about a strong decrease in the respiratory
control ratio. This is suggestive of a high rate of formation of phosphate
acceptors which lower the respiratory control (Lardy and Wellman,
1952) and hence produce a heavy drain on energy-rich compounds.
ALBERTO MONROY AND RACHELE MAGGIO
distribution of the mitochondria (as judged by the above criteria) is
almost equal to that found in the unfertilized eggs.
A further point to be taken into consideration is that the rationale
behind the technique of homogenization and preparation of cell
components by differential centrifugation is the assumption that all the
cells of the system under consideration are endowed with the same
properties. In the case of the embryo this is evidently a gratuitous
assumption and indeed a quite erroneous one. It may just be mentioned
here that in the mesenchyme blastula the uptake of labelled amino-acids
is considerably lower in the cells of the primary mesenchyme and in the
entire vegetative territory than in the rest of the larva (Bosco and
Monroy, 1962).
III. Protein Synthesis During the Early Development
of the Sea Urchin
A. General Metabolic Background
The general metabolic background of the development of the sea
urchin egg is best outlined by the well-known S-shaped respiratory
curve (Lindahl, 1939 ; Borei, 1948). A first period of exponential increase
from fertilization to the early blastula is followed by a plateau extending
somewhat beyond the hatching of the embryo and then by a second
period of quite steep increase in oxygen consumption beginning a little
before the appearance of the primary mesenchyme. The shape of the
curve indicating the rate of increase of the cell population (Köhler, 1912 ;
Zeuthen, 1953) duplicates that of oxygen consumption (Fig. 1). In a
series of papers Zeuthen (summarized in 1953) has given evidence of a
respiratory rhythm accompanying cell division and indeed of increasing
rates of respiration at the stages where nuclei reappear and persist.
According to this author the decisive factor in the exponential increase
of respiration during cleavage is the increasing ratio of 'whole' (i.e.,
surrounded by a membrane) to 'open' nuclei which holds good till about
the 10th cleavage. At this point cleavages and increase of respiration
both come to a standstill and then resume again at the late blastula
stage. Zeuthen (1953) has also drawn attention to the coincidence
between the phases of respiratory increase during the mitotic cycle and
DNA synthesis.
Recently Immers and Runnström (1960) observed that treatment of
the eggs with 2 : 4 dinitrophenol during the period of exponential
respiratory increase brings about a strong decrease in the respiratory
control ratio. This is suggestive of a high rate of formation of phosphate
acceptors which lower the respiratory control (Lardy and Wellman,
1952) and hence produce a heavy drain on energy-rich compounds.