NUCLEIC ACIDS AND SULPHYDRYL GROUPS
249
of cleavage (mitosis), gastrulation (cell movements) and nervous system
differentiation (induction). With Acetabularia, the main question will be
the role of the cell nucleus in morphogenesis and in nucleic acid and
protein synthesis.
Another limitation in this review is that it will be impossible to deal
with all proteins. We have restricted ourselves to one of the most
reactive bonds, the sulphur-containing ones. Fortunately, a detailed
study of enzyme synthesis during embryonic development has been
published by Urbani in the last volume of this series. It is a well-known
fact that the biological activity of many enzymes and hormones and the
molecular structure of most—if not all—proteins, depend upon the
integrity of these sulphur-containing bonds or groups: the most
important ones are the sulphydryl (—SH, thiol) group and its oxidized
counterpart (—S—S—, disulphide). We shall see that the addition to the
medium of —SH or —S—S— containing compounds often has farreaching consequences for developing organisms.
A few words will also be said about basic proteins, in view of their
close association with nucleic acids in ribosomes (Crampton and
Petermann, 1959) as well as in chromatin. Mention will also be made, in
a cursory fashion, of protein synthesis in Acetabularia, since this subject
has not yet been treated in 'Advances in Morphogenesis'.
In this review, we shall respectfully follow the accepted order of
hierarchy : starting with DNA, we shall go into the problems raised by
the RNA's and finish with protein sulphydryl groups. In the final
discussion, an attempt will be made to give an interpretation of the
facts in terms of the current concepts in molecular biology which have
been outlined above.
II. DNA in Amphibian Eggs and Acetabularia
A. Amphibian Egg Development
1. DNA Synthesis During
Development
Multiplication of the cell nuclei, during cleavage, is an obvious requirement for the morphogenetic movements characteristic of gastrulation and neurulation: only relatively small cells have the plasticity
required for this phase of development.
One would expect cleavage to be a period of intensive DNA synthesis;
however, the problem is complicated by the existence of a so-called
'DNA cytoplasmic reserve'.
The most specific techniques for DNA estimation, for the time being,
are the microbiological ones. They show that amphibian eggs contain, at
the beginning, an excess of DNA which is sufficient to reach the late
blastula stage (about 5,000 to 10,000 cells) (Hoff-Jorgensen, 1954;
249
of cleavage (mitosis), gastrulation (cell movements) and nervous system
differentiation (induction). With Acetabularia, the main question will be
the role of the cell nucleus in morphogenesis and in nucleic acid and
protein synthesis.
Another limitation in this review is that it will be impossible to deal
with all proteins. We have restricted ourselves to one of the most
reactive bonds, the sulphur-containing ones. Fortunately, a detailed
study of enzyme synthesis during embryonic development has been
published by Urbani in the last volume of this series. It is a well-known
fact that the biological activity of many enzymes and hormones and the
molecular structure of most—if not all—proteins, depend upon the
integrity of these sulphur-containing bonds or groups: the most
important ones are the sulphydryl (—SH, thiol) group and its oxidized
counterpart (—S—S—, disulphide). We shall see that the addition to the
medium of —SH or —S—S— containing compounds often has farreaching consequences for developing organisms.
A few words will also be said about basic proteins, in view of their
close association with nucleic acids in ribosomes (Crampton and
Petermann, 1959) as well as in chromatin. Mention will also be made, in
a cursory fashion, of protein synthesis in Acetabularia, since this subject
has not yet been treated in 'Advances in Morphogenesis'.
In this review, we shall respectfully follow the accepted order of
hierarchy : starting with DNA, we shall go into the problems raised by
the RNA's and finish with protein sulphydryl groups. In the final
discussion, an attempt will be made to give an interpretation of the
facts in terms of the current concepts in molecular biology which have
been outlined above.
II. DNA in Amphibian Eggs and Acetabularia
A. Amphibian Egg Development
1. DNA Synthesis During
Development
Multiplication of the cell nuclei, during cleavage, is an obvious requirement for the morphogenetic movements characteristic of gastrulation and neurulation: only relatively small cells have the plasticity
required for this phase of development.
One would expect cleavage to be a period of intensive DNA synthesis;
however, the problem is complicated by the existence of a so-called
'DNA cytoplasmic reserve'.
The most specific techniques for DNA estimation, for the time being,
are the microbiological ones. They show that amphibian eggs contain, at
the beginning, an excess of DNA which is sufficient to reach the late
blastula stage (about 5,000 to 10,000 cells) (Hoff-Jorgensen, 1954;