130
ALBERTO MONROY AND RACHELE MAGGIO
oxidase—also in this case as measured on the isolated mitochondria—
after a slight increase immediately following fertilization, remains
constant at least until the blastula stage (Maggio, 1959). It seems of
interest however, to mention the work of Berg et al. (1962) who observed
in the cells of the vegetative territory of the sea urchin blastula that the
mitochondria had a 'swollen' appearance which did not seem to be due
to faulty techniques. The authors suggest that the larger mitochondria
in the vegetal region may be an explanation of the vegetal-animal
gradient linked not to the number of mitochondria but rather to a
gradient of mitochondrial enzymes. It may be pertinent to recall that
swollen mitochondria have been observed by Wigglesworth (1957) in the
epidermal cells of insects as a first indication of an 'activation' process
due either to the moulting hormone or to an injury.
Indirect evidence concerning changes in the mitochondria in the
course of sea urchin development comes from a number of physiological
and biochemical experiments.
Swelling in hypotonic media or in the presence of detergents is significantly greater in the mitochondria from unfertilized than from newly
fertilized eggs (Monroy, 1957a), a fact that has been interpreted as being
due to a change in the ultrastructure of the mitochondrial membrane.
Nakano and Tsusaka (1961) have shown that whilst the uptake of
3 2 P by
isolated mitochondria from unfertilized eggs is inhibited by DNP,
uptake by the mitochondria prepared from eggs immediately after
fertilization is not. On the other hand, when the effect of DNP is tested
on the intact egg it is found that the uptake by the unfertilized egg is
inhibited, while after fertilization there is a decline of this effect until
complete insensitivity to DNP is reached at about 30 minutes after
fertilization (see also Bolst and Whiteley, 1957). These interesting
observations indicate that, while the metabolic pathway for
3 2
P
incorporation is only established in the course of about 30 minutes after
fertilization, in the mitochondria themselves some kind of sudden
change takes place immediately after fertilization.
However, the changes now indicated, although certainly related to
the initiation of morphogenesis, can probably be more rightly considered
as being related to the process of the activation of the egg rather than of
morphogenesis proper. Indeed it has been suggested that one of the key
events in fertilization is the activation of the mitochondria (Monroy,
1953 ; Nakano and Monroy, 1958).
As previously mentioned, in eggs pre-labelled with radioactive aminoacids, almost immediately following fertilization the mitochondria begin
to take up the labelled compound, whereas no uptake occurs in the
unfertilized egg. This may be taken as an indication of a change of some
kind occurring in the mitochondria. However, this now seems likely to
ALBERTO MONROY AND RACHELE MAGGIO
oxidase—also in this case as measured on the isolated mitochondria—
after a slight increase immediately following fertilization, remains
constant at least until the blastula stage (Maggio, 1959). It seems of
interest however, to mention the work of Berg et al. (1962) who observed
in the cells of the vegetative territory of the sea urchin blastula that the
mitochondria had a 'swollen' appearance which did not seem to be due
to faulty techniques. The authors suggest that the larger mitochondria
in the vegetal region may be an explanation of the vegetal-animal
gradient linked not to the number of mitochondria but rather to a
gradient of mitochondrial enzymes. It may be pertinent to recall that
swollen mitochondria have been observed by Wigglesworth (1957) in the
epidermal cells of insects as a first indication of an 'activation' process
due either to the moulting hormone or to an injury.
Indirect evidence concerning changes in the mitochondria in the
course of sea urchin development comes from a number of physiological
and biochemical experiments.
Swelling in hypotonic media or in the presence of detergents is significantly greater in the mitochondria from unfertilized than from newly
fertilized eggs (Monroy, 1957a), a fact that has been interpreted as being
due to a change in the ultrastructure of the mitochondrial membrane.
Nakano and Tsusaka (1961) have shown that whilst the uptake of
3 2 P by
isolated mitochondria from unfertilized eggs is inhibited by DNP,
uptake by the mitochondria prepared from eggs immediately after
fertilization is not. On the other hand, when the effect of DNP is tested
on the intact egg it is found that the uptake by the unfertilized egg is
inhibited, while after fertilization there is a decline of this effect until
complete insensitivity to DNP is reached at about 30 minutes after
fertilization (see also Bolst and Whiteley, 1957). These interesting
observations indicate that, while the metabolic pathway for
3 2
P
incorporation is only established in the course of about 30 minutes after
fertilization, in the mitochondria themselves some kind of sudden
change takes place immediately after fertilization.
However, the changes now indicated, although certainly related to
the initiation of morphogenesis, can probably be more rightly considered
as being related to the process of the activation of the egg rather than of
morphogenesis proper. Indeed it has been suggested that one of the key
events in fertilization is the activation of the mitochondria (Monroy,
1953 ; Nakano and Monroy, 1958).
As previously mentioned, in eggs pre-labelled with radioactive aminoacids, almost immediately following fertilization the mitochondria begin
to take up the labelled compound, whereas no uptake occurs in the
unfertilized egg. This may be taken as an indication of a change of some
kind occurring in the mitochondria. However, this now seems likely to