N U C L E I O A C I D S A N D S U L P H Y D R Y L G R O U P S
265
FIG. 10. The dorsal lip of a frog gastrula treated as in Fig. 9 has been transplanted into
a normal axolotl gastrula: it has differentiated into chorda, somites and archenteron
(dark), and it has induced several neural nodules in the host.
R N A in d e v e l o p m e n t b y s u b m i t t i n g living a m p h i b i a n eggs t o t h e action
of R N a s e .
I t was found t h a t t h e eggs which h a v e been t r e a t e d for a few h o u r s
w i t h R N a s e a t t h e n e u r u l a stage, form a n atypical e c t o d e r m w h e n t h e y
a r e r e t u r n e d t o n o r m a l m e d i u m . B u t , t h e y can produce a n e r v o u s
s y s t e m if t h e y are t r e a t e d w i t h a R N a s e - R N A m i x t u r e (Brächet a n d
L e d o u x , 1955) (Figs. 11,12). Ribonuclease, if s u p p l e m e n t e d with Versene,
can lead t o t h e production of 'ectodermless' e m b r y o s , w h e n t r e a t m e n t
begins a t t h e g a s t r u l a or n e u r u l a s t a g e : these e m b r y o s h a v e welldifferentiated chorda a n d somites, b u t no n e r v o u s system.
4. Neural Induction by Purified
Fractions
Since this question h a s been t h e subject of a n excellent review b y
Y a m a d a (1961) in Vol. 1 of 'Advances in Morphogenesis', we shall be as
brief as possible. I t now seems clear t h a t , as we found in 1944, ribonucleoproteins of different origins are actively inducing substances. B u t
w h e t h e r R N A itself is absolutely required for inducing a c t i v i t y seems
now m o s t unlikely ( Y a m a d a , 1961). T h e r e can be no possible discussion
of one point, which h a s been well-demonstrated b y t h e Y a m a d a a n d
T i e d e m a n n schools : p u r e proteins, devoid of R N A , can induce mesoderm,
265
FIG. 10. The dorsal lip of a frog gastrula treated as in Fig. 9 has been transplanted into
a normal axolotl gastrula: it has differentiated into chorda, somites and archenteron
(dark), and it has induced several neural nodules in the host.
R N A in d e v e l o p m e n t b y s u b m i t t i n g living a m p h i b i a n eggs t o t h e action
of R N a s e .
I t was found t h a t t h e eggs which h a v e been t r e a t e d for a few h o u r s
w i t h R N a s e a t t h e n e u r u l a stage, form a n atypical e c t o d e r m w h e n t h e y
a r e r e t u r n e d t o n o r m a l m e d i u m . B u t , t h e y can produce a n e r v o u s
s y s t e m if t h e y are t r e a t e d w i t h a R N a s e - R N A m i x t u r e (Brächet a n d
L e d o u x , 1955) (Figs. 11,12). Ribonuclease, if s u p p l e m e n t e d with Versene,
can lead t o t h e production of 'ectodermless' e m b r y o s , w h e n t r e a t m e n t
begins a t t h e g a s t r u l a or n e u r u l a s t a g e : these e m b r y o s h a v e welldifferentiated chorda a n d somites, b u t no n e r v o u s system.
4. Neural Induction by Purified
Fractions
Since this question h a s been t h e subject of a n excellent review b y
Y a m a d a (1961) in Vol. 1 of 'Advances in Morphogenesis', we shall be as
brief as possible. I t now seems clear t h a t , as we found in 1944, ribonucleoproteins of different origins are actively inducing substances. B u t
w h e t h e r R N A itself is absolutely required for inducing a c t i v i t y seems
now m o s t unlikely ( Y a m a d a , 1961). T h e r e can be no possible discussion
of one point, which h a s been well-demonstrated b y t h e Y a m a d a a n d
T i e d e m a n n schools : p u r e proteins, devoid of R N A , can induce mesoderm,