280
JEAN BRÄCHET
(Brächet, 1958b, 1959a-d, 1960). The algae, whether they are nucleate
or anucleate, grow steadily in the presence of M/300 mercaptoethanol,
but they do not form caps. If small caps are present at the time of
section, they never grow to an appreciable extent in anucleate fragments.
On the other hand, the production of the sterile whorls, which should
normally give rise to caps, proceeds for a long time.
Since mercaptoethanol so strongly inhibits morphogenesis (i.e., cap
formation) in Acetabularia, as well as in amphibian embryos, it became
of interest to study the effects of dithiodiglycol on this alga. The
results of these experiments were fairly clear : while mercaptoethanol
inhibited cap formation without exerting ill effects on the production of
whorls, dithiodiglycol (M/10,000) had exactly the opposite effect of
stimulating cap production and inhibiting the formation of the sterile
whorls.
In order to study further the role of sulphydryl groups in cap
formation, the effects of some of the 'classical' sulphydryl reagents on
the regeneration of nucleate and anucleate Acetabularia fragments have
been studied. Two of them, p-chloromercuribenzoate (10
_7 M) and
p-iodosobenzoic acid (10
-5 M) exerted definitely favourable effects on cap
formation in anucleate fragments, but iodoacetamide did not. These
observations indicate, on the whole, that an excess of thiol groups is
detrimental to the production of caps, and that a moderate decrease
in these groups is favourable for morphogenesis (as in amphibian
embryos).
Similar observations have been made in the case of the regeneration
of the tail of tadpoles (Brächet, 1959a-d, 1960; Descotils-Heernu et al.,
1961) which is completely inhibited by mercaptoethanol M/300 (Figs.
14, 15). Four days after the section, there is almost no regenerating
blastema and the tadpoles are still unable to swim properly. Since
mitoses are far from absent, the inhibition of blastema formation is
probably due to a reduction of cell migration and, possibly, to an
incapacity of the sectioned chorda to elongate normally.
Dithiodiglycol (M/1,000), on the other hand, does not at all prevent
regeneration, which may even occasionally be faster than in the controls.
The mesenchyme of the regenerating tail is particularly basophilic, and
its mitotic activity is high.
The effects of the —SH^—S S— equilibrium on the regeneration of the
head in planarians have also been studied (Brächet, 1959a-d, 1960;
Descotils et al., 1961). Despite some difficulties, the following general
conclusions can be drawn: mercaptoethanol (M/300 to M/1,000) again
exerts a considerable inhibitory effect on the regeneration of planarians
that have been sectioned in front of the pharynx. In most cases, no
formation of blastema can be seen in the living organisms or sections.
JEAN BRÄCHET
(Brächet, 1958b, 1959a-d, 1960). The algae, whether they are nucleate
or anucleate, grow steadily in the presence of M/300 mercaptoethanol,
but they do not form caps. If small caps are present at the time of
section, they never grow to an appreciable extent in anucleate fragments.
On the other hand, the production of the sterile whorls, which should
normally give rise to caps, proceeds for a long time.
Since mercaptoethanol so strongly inhibits morphogenesis (i.e., cap
formation) in Acetabularia, as well as in amphibian embryos, it became
of interest to study the effects of dithiodiglycol on this alga. The
results of these experiments were fairly clear : while mercaptoethanol
inhibited cap formation without exerting ill effects on the production of
whorls, dithiodiglycol (M/10,000) had exactly the opposite effect of
stimulating cap production and inhibiting the formation of the sterile
whorls.
In order to study further the role of sulphydryl groups in cap
formation, the effects of some of the 'classical' sulphydryl reagents on
the regeneration of nucleate and anucleate Acetabularia fragments have
been studied. Two of them, p-chloromercuribenzoate (10
_7 M) and
p-iodosobenzoic acid (10
-5 M) exerted definitely favourable effects on cap
formation in anucleate fragments, but iodoacetamide did not. These
observations indicate, on the whole, that an excess of thiol groups is
detrimental to the production of caps, and that a moderate decrease
in these groups is favourable for morphogenesis (as in amphibian
embryos).
Similar observations have been made in the case of the regeneration
of the tail of tadpoles (Brächet, 1959a-d, 1960; Descotils-Heernu et al.,
1961) which is completely inhibited by mercaptoethanol M/300 (Figs.
14, 15). Four days after the section, there is almost no regenerating
blastema and the tadpoles are still unable to swim properly. Since
mitoses are far from absent, the inhibition of blastema formation is
probably due to a reduction of cell migration and, possibly, to an
incapacity of the sectioned chorda to elongate normally.
Dithiodiglycol (M/1,000), on the other hand, does not at all prevent
regeneration, which may even occasionally be faster than in the controls.
The mesenchyme of the regenerating tail is particularly basophilic, and
its mitotic activity is high.
The effects of the —SH^—S S— equilibrium on the regeneration of the
head in planarians have also been studied (Brächet, 1959a-d, 1960;
Descotils et al., 1961). Despite some difficulties, the following general
conclusions can be drawn: mercaptoethanol (M/300 to M/1,000) again
exerts a considerable inhibitory effect on the regeneration of planarians
that have been sectioned in front of the pharynx. In most cases, no
formation of blastema can be seen in the living organisms or sections.