EARLY DEVELOPMENT OF THE SEA URCHIN
135
et al., 1958) was obtained with ribosomes from eggs artificially activated
by butyric acid (Hultin, 1961).
That a structural rearrangement of the ribosomes at the molecular
level taking place as a result of fertilization may be responsible for the
activation (Hultin and Bergstrand, 1960; Hultin, 1961) seems to be
quite a reasonable working hypothesis. It would be very interesting if
direct evidence of this structural change of the ribosomes could be
produced. Recent work (Lamfrom and Glowacki, 1962) has shown that
ribosomes of rabbit reticulocytes dissociated into sub-units lose their
ability to incorporate amino-acids into proteins. This may suggest the
possibility that in the unfertilized egg the ribosomal sub-units might be
relatively dissociated, complete association being brought about as a
result of fertilization.
In recent times the older concept of the microsomes as the site
containing the specific template for the synthesis of the various proteins
has been modified by the recognition of the metabolically active
'messenger' RNA which appears to be the actual transmitter of the
genetical information from the nucleus to the microsomes. The latter are
merely endowed with the ability of peptide-bonding the amino-acids in
the specific sequence imparted by the messenger RNA.
Anyway there is no doubt that in the final phase of their synthesis
protein molecules are associated with the microsomes. The fact that in
the unfertilized eggs the ribosomes have been found to be unable to
accomplish protein synthesis is certainly interesting but it would be of
the utmost importance also to find out whether any messenger RNA at
all is present in the unfertilized egg. In fact it might be supposed that in
the unfertilized egg either the synthesis of messenger RNA is suppressed
or, although being produced, for some reason it cannot establish contact
with the ribosomes.f As yet, however, nothing is known about the
messenger RNA of the sea urchin egg and, as noted earlier (Section IV,
B, 2), very little indeed is known about the metabolism and the various
fractions of RNA in general.
D. The Yolk Platelets
The biochemical study of the changes taking place in the yolk in the
course of sea urchin development is very difficult because the yolk
platelets are more or less uniformly distributed throughout the cytot The manuscript of this review had already been delivered when we came across a
paper by Nemer (1962) in which it is shown that the ribosomal activity of the unfertilized
eggs is strongly stimulated by synthetic polyribonucleotides. Following fertilization and
in the course of development the ability of ribosomes to respond to such addition progressively decreases. The author suggests that the result may be due to the ribosomes of
the unfertilized egg being naturally stripped of messenger RNA. Following fertilization,
the messenger RNA would be synthesized and become attached to the particles.
135
et al., 1958) was obtained with ribosomes from eggs artificially activated
by butyric acid (Hultin, 1961).
That a structural rearrangement of the ribosomes at the molecular
level taking place as a result of fertilization may be responsible for the
activation (Hultin and Bergstrand, 1960; Hultin, 1961) seems to be
quite a reasonable working hypothesis. It would be very interesting if
direct evidence of this structural change of the ribosomes could be
produced. Recent work (Lamfrom and Glowacki, 1962) has shown that
ribosomes of rabbit reticulocytes dissociated into sub-units lose their
ability to incorporate amino-acids into proteins. This may suggest the
possibility that in the unfertilized egg the ribosomal sub-units might be
relatively dissociated, complete association being brought about as a
result of fertilization.
In recent times the older concept of the microsomes as the site
containing the specific template for the synthesis of the various proteins
has been modified by the recognition of the metabolically active
'messenger' RNA which appears to be the actual transmitter of the
genetical information from the nucleus to the microsomes. The latter are
merely endowed with the ability of peptide-bonding the amino-acids in
the specific sequence imparted by the messenger RNA.
Anyway there is no doubt that in the final phase of their synthesis
protein molecules are associated with the microsomes. The fact that in
the unfertilized eggs the ribosomes have been found to be unable to
accomplish protein synthesis is certainly interesting but it would be of
the utmost importance also to find out whether any messenger RNA at
all is present in the unfertilized egg. In fact it might be supposed that in
the unfertilized egg either the synthesis of messenger RNA is suppressed
or, although being produced, for some reason it cannot establish contact
with the ribosomes.f As yet, however, nothing is known about the
messenger RNA of the sea urchin egg and, as noted earlier (Section IV,
B, 2), very little indeed is known about the metabolism and the various
fractions of RNA in general.
D. The Yolk Platelets
The biochemical study of the changes taking place in the yolk in the
course of sea urchin development is very difficult because the yolk
platelets are more or less uniformly distributed throughout the cytot The manuscript of this review had already been delivered when we came across a
paper by Nemer (1962) in which it is shown that the ribosomal activity of the unfertilized
eggs is strongly stimulated by synthetic polyribonucleotides. Following fertilization and
in the course of development the ability of ribosomes to respond to such addition progressively decreases. The author suggests that the result may be due to the ribosomes of
the unfertilized egg being naturally stripped of messenger RNA. Following fertilization,
the messenger RNA would be synthesized and become attached to the particles.