NUCLEIC ACIDS AND SULPHYDRYL GROUPS
275
sea urchin eggs, by Runnström and Kriszat (1952), Lallier (1951, 1963a,
b) and Bäckström (1958,1959).
In the case of amphibian eggs, the effects on morphogenesis of a number of 'classical' sulphydryl reagents (monoiodo-acetic acid, monoiodoacetamide, chloropicrine, chloro-acetaphenone, oxidized glutathione,
arsenite, etc.) have been studied by a number of authors (Brächet, 1944 ;
Beatty, 1949; Rapkine and Brächet, 1951; Lallier, 1951; Barth, 1956;
Deuchar, 1957; ten Cate, 1957; etc.). These agents all produce similar
effects: the nervous system remains a thick, open plate, while the
differentiation of chorda and somites is relatively normal.
More recently, the effects on amphibian morphogenesis and regeneration in Acetabularia of new sulphydryl reagents, introduced in biological
research by Mazia (1958a, b) in his important studies on mitosis in sea
urchin eggs, have been investigated in our laboratory. These agents are
^-mercaptoethanol
(HSCH 2 -CH 2 OH), which is strongly reducing,
penetrates easily into living cells and is relatively non-toxic, and its
oxidized counterpart, dithiodiglycol
(HOCH 2 -CH 2 -S-S-CH 2 -CH 2 OH),
which easily oxidizes —SH groups of proteins, and
mercaptoethylgluconamide, a derivative of mercaptoethanol which does not penetrate
easily into the cells and is especially useful for control experiments.
As we shall see in greater detail, mercaptoethanol exerts inhibitory
effects on a great variety of morphogenetic systems (amphibian and
avian embryos, regenerating tadpoles, hydra and planarians, nucleate
and anucleate fragments oî Acetabularia).
These remarkable properties
are shared by a cyclic disulphide, oc-lipoic acid : inhibition of regeneration
in hydra and planarians by low concentrations of lipoic acid was first
demonstrated by Henderson and Eakin (1959) and by Ham and Eakin
(1958).
In the following, the effects on morphogenesis of mercaptoethanol
and
its derivatives will first be discussed ; a second section will be devoted to
the inhibition of morphogenesis by lipoic acid. Finally, a summary of
what is known concerning the biochemical effects of mercaptoethanol
on
developing systems will be presented.
B. The Effects of ^-Mercaptoethanol on Morphogenesis
1. Amphibian Egg Development
The most conspicuous result obtained when amphibian gastrulae or
neurulae are treated with mercaptoethanol (M/100 to M/300) is the
complete cessation of morphogenetic movements (Brächet and DelangeCornil, 1959; Seilern-Aspang, 1959; Brächet, 1960). However, mercaptoethanol is relatively non-toxic, especially during neurulation, and the
blocked embryos survive for several days. Experiments in which
275
sea urchin eggs, by Runnström and Kriszat (1952), Lallier (1951, 1963a,
b) and Bäckström (1958,1959).
In the case of amphibian eggs, the effects on morphogenesis of a number of 'classical' sulphydryl reagents (monoiodo-acetic acid, monoiodoacetamide, chloropicrine, chloro-acetaphenone, oxidized glutathione,
arsenite, etc.) have been studied by a number of authors (Brächet, 1944 ;
Beatty, 1949; Rapkine and Brächet, 1951; Lallier, 1951; Barth, 1956;
Deuchar, 1957; ten Cate, 1957; etc.). These agents all produce similar
effects: the nervous system remains a thick, open plate, while the
differentiation of chorda and somites is relatively normal.
More recently, the effects on amphibian morphogenesis and regeneration in Acetabularia of new sulphydryl reagents, introduced in biological
research by Mazia (1958a, b) in his important studies on mitosis in sea
urchin eggs, have been investigated in our laboratory. These agents are
^-mercaptoethanol
(HSCH 2 -CH 2 OH), which is strongly reducing,
penetrates easily into living cells and is relatively non-toxic, and its
oxidized counterpart, dithiodiglycol
(HOCH 2 -CH 2 -S-S-CH 2 -CH 2 OH),
which easily oxidizes —SH groups of proteins, and
mercaptoethylgluconamide, a derivative of mercaptoethanol which does not penetrate
easily into the cells and is especially useful for control experiments.
As we shall see in greater detail, mercaptoethanol exerts inhibitory
effects on a great variety of morphogenetic systems (amphibian and
avian embryos, regenerating tadpoles, hydra and planarians, nucleate
and anucleate fragments oî Acetabularia).
These remarkable properties
are shared by a cyclic disulphide, oc-lipoic acid : inhibition of regeneration
in hydra and planarians by low concentrations of lipoic acid was first
demonstrated by Henderson and Eakin (1959) and by Ham and Eakin
(1958).
In the following, the effects on morphogenesis of mercaptoethanol
and
its derivatives will first be discussed ; a second section will be devoted to
the inhibition of morphogenesis by lipoic acid. Finally, a summary of
what is known concerning the biochemical effects of mercaptoethanol
on
developing systems will be presented.
B. The Effects of ^-Mercaptoethanol on Morphogenesis
1. Amphibian Egg Development
The most conspicuous result obtained when amphibian gastrulae or
neurulae are treated with mercaptoethanol (M/100 to M/300) is the
complete cessation of morphogenetic movements (Brächet and DelangeCornil, 1959; Seilern-Aspang, 1959; Brächet, 1960). However, mercaptoethanol is relatively non-toxic, especially during neurulation, and the
blocked embryos survive for several days. Experiments in which