15. E M B R Y O G E N E S I S in vitro
571
non-existent, but where differentiation is nevertheless active, the
incorporation of
1 4
C glycine into cellular proteins increases. Thus, it is
a likely assumption that the requirements of growth and of differentiation are different: this difference might be due to the fact that
the precursors of the proteins are not the same in the two cases (Hayashi
and Herrmann, 1959).
5. The Action of Metabolic Inhibitors
Preceding investigations have shown that regions of rapid differentiation, such as Hensen's node and the anterior brain, have a high metabolic activity and are more sensitive to nutritive deficiencies. Analogous
results may be suspected from investigations using inhibitors of enzymatic reactions.
(a). Inhibitors. Spratt (1950b) used various metabolic inhibitors:
monoiodoacetate; fluoride; citrate; malonate; cyanide; and sodium
azide. Blastoderms were cultivated in vitro, beginning at a stage between
the definitive primitive streak and the five-somites stage. The general
results were as follows, (i). At a concentration of 1 0
- 4 M, the monoiodoacetate provoked total disintegration of the whole embryo. At lower
concentrations, the nervous system was particularly affected at those
points where differentiation is most active (prosencephalon and the
neural tube), but the heart was much more resistant; it differentiated
and started to beat. The harmful effects of monoiodoacetate on the
nervous system could be remedied in part by adding sodium pyruvate
to the substrate of glucose. In this way, too, differentiation of the
somites could be started up again.
The fact that the action of this inhibitor could be circumvented by
the addition of the pyruvate suggests that the former inhibits the action
of triosephosphate dehydrogenase. The fact that the effects on the
heart and on the nervous system are different tends to prove that
oxidative metabolism is less intense in the one organ than in the other.
(ii). Sodium fluoride exercised a differential inhibiting action opposite to that of monoiodoacetate. It did not affect the nervous system,
but, at a concentration of 5 x 1 0
- 3 M, it prevented the differentiation of
the heart and caused its disintegration. At the same time as the heart,
various other mesodermal organs were inhibited (somites and lateral
plates). Stronger doses (10~
2 M) caused disintegration of all the systems.
But the addition of pyruvate to the glucose substrate protected the
development and differentiation of the nervous system against these
stronger doses.
Sodium fluoride may be an inhibitor of enolase activity. The great
sensitivity of the heart to this inhibitor suggests that this organ obtains
much of its energy from glycolysis.
571
non-existent, but where differentiation is nevertheless active, the
incorporation of
1 4
C glycine into cellular proteins increases. Thus, it is
a likely assumption that the requirements of growth and of differentiation are different: this difference might be due to the fact that
the precursors of the proteins are not the same in the two cases (Hayashi
and Herrmann, 1959).
5. The Action of Metabolic Inhibitors
Preceding investigations have shown that regions of rapid differentiation, such as Hensen's node and the anterior brain, have a high metabolic activity and are more sensitive to nutritive deficiencies. Analogous
results may be suspected from investigations using inhibitors of enzymatic reactions.
(a). Inhibitors. Spratt (1950b) used various metabolic inhibitors:
monoiodoacetate; fluoride; citrate; malonate; cyanide; and sodium
azide. Blastoderms were cultivated in vitro, beginning at a stage between
the definitive primitive streak and the five-somites stage. The general
results were as follows, (i). At a concentration of 1 0
- 4 M, the monoiodoacetate provoked total disintegration of the whole embryo. At lower
concentrations, the nervous system was particularly affected at those
points where differentiation is most active (prosencephalon and the
neural tube), but the heart was much more resistant; it differentiated
and started to beat. The harmful effects of monoiodoacetate on the
nervous system could be remedied in part by adding sodium pyruvate
to the substrate of glucose. In this way, too, differentiation of the
somites could be started up again.
The fact that the action of this inhibitor could be circumvented by
the addition of the pyruvate suggests that the former inhibits the action
of triosephosphate dehydrogenase. The fact that the effects on the
heart and on the nervous system are different tends to prove that
oxidative metabolism is less intense in the one organ than in the other.
(ii). Sodium fluoride exercised a differential inhibiting action opposite to that of monoiodoacetate. It did not affect the nervous system,
but, at a concentration of 5 x 1 0
- 3 M, it prevented the differentiation of
the heart and caused its disintegration. At the same time as the heart,
various other mesodermal organs were inhibited (somites and lateral
plates). Stronger doses (10~
2 M) caused disintegration of all the systems.
But the addition of pyruvate to the glucose substrate protected the
development and differentiation of the nervous system against these
stronger doses.
Sodium fluoride may be an inhibitor of enolase activity. The great
sensitivity of the heart to this inhibitor suggests that this organ obtains
much of its energy from glycolysis.