ANIMALIZATION AND VEGETALIZATION
191
the formation of reduction gradients. The results obtained from studying
the distribution of incorporated labelled molecules also suggest a
distribution in a gradient of nucleic acid and protein synthesis.
As a rule, the distribution of the gradients of metabolic activity may
be related to the existence of inhibitory factors; metabolic activity
being more or less intense according to the degree of inhibition exerted
by these factors. According to a suggestion from Rose (1952), differentiation depends on the inhibition of gene reactions. Kriszat and
Runnström (1957) have suggested, in the sea urchin egg, the existence
of a factor depressing metabolism at the vegetal pole. The study of
micro-organisms has given numerous examples showing the importance
of inhibitory phenomenon in the regulation of cellular activity. Thus,
research on the induced synthesis of enzymes has clarified the role of the
phenomenon of repression in the control of enzymatic synthesis (Jacob
and Monod, 1961). From these new concepts, Monod and Jacob (1961)
have elaborated theoretical models for the interpretation of differentiation. The introduction of the concept of inhibition in the analysis of
the development of the sea urchin egg suggests an interpretation of
differentiation and the mode of action of the animalizing and vegetalizing
agents. At the very beginning of development the nuclei would emit
information of animal or vegetal type. This information would specifically orientate protein synthesis. The activation of the synthesis
of animal proteins would inhibit the synthesis of the vegetal proteins
and vice versa. At the beginning of development, the synthesis of animal
proteins would be favoured at the animal pole, while the synthesis of
vegetal proteins would be favoured at the vegetal pole. The local
advantage favouring a special type of protein synthesis at each pole
might be connected to some structural peculiarity at the pole of the eggs,
perhaps in relation to the cortex. The importance of the cortex in differentiation has already been emphasized by Raven (1958) who suggests that
part of the information necessary to development exists as a blue print in
the cortex. According to the general scheme that we have just indicated,
animalizing and vegetalizing agents would influence morphogenesis by
acting directly as inhibitors, or indirectly by favouring the formation of
inhibitors of the synthesis of specific proteins.
References
Abruzzese Sgarlata, S. (1947). Ric. set. Mem. 17, 473.
Afzelius, B. A. (1956). Exp. Cell Res. 11, 67.
Afzelius, B. A. (1957a). Z. Zellforsch. 45, 660.
Afzelius, B. A. (1957b). 'Electron Microscopy on Sea-urchin Gametes', Almqvist
and Wiksells Boktryckeri AB, Uppsala.
Agrell, I. and Persson, H. (1956). Nature, Lond. 178, 1398.
191
the formation of reduction gradients. The results obtained from studying
the distribution of incorporated labelled molecules also suggest a
distribution in a gradient of nucleic acid and protein synthesis.
As a rule, the distribution of the gradients of metabolic activity may
be related to the existence of inhibitory factors; metabolic activity
being more or less intense according to the degree of inhibition exerted
by these factors. According to a suggestion from Rose (1952), differentiation depends on the inhibition of gene reactions. Kriszat and
Runnström (1957) have suggested, in the sea urchin egg, the existence
of a factor depressing metabolism at the vegetal pole. The study of
micro-organisms has given numerous examples showing the importance
of inhibitory phenomenon in the regulation of cellular activity. Thus,
research on the induced synthesis of enzymes has clarified the role of the
phenomenon of repression in the control of enzymatic synthesis (Jacob
and Monod, 1961). From these new concepts, Monod and Jacob (1961)
have elaborated theoretical models for the interpretation of differentiation. The introduction of the concept of inhibition in the analysis of
the development of the sea urchin egg suggests an interpretation of
differentiation and the mode of action of the animalizing and vegetalizing
agents. At the very beginning of development the nuclei would emit
information of animal or vegetal type. This information would specifically orientate protein synthesis. The activation of the synthesis
of animal proteins would inhibit the synthesis of the vegetal proteins
and vice versa. At the beginning of development, the synthesis of animal
proteins would be favoured at the animal pole, while the synthesis of
vegetal proteins would be favoured at the vegetal pole. The local
advantage favouring a special type of protein synthesis at each pole
might be connected to some structural peculiarity at the pole of the eggs,
perhaps in relation to the cortex. The importance of the cortex in differentiation has already been emphasized by Raven (1958) who suggests that
part of the information necessary to development exists as a blue print in
the cortex. According to the general scheme that we have just indicated,
animalizing and vegetalizing agents would influence morphogenesis by
acting directly as inhibitors, or indirectly by favouring the formation of
inhibitors of the synthesis of specific proteins.
References
Abruzzese Sgarlata, S. (1947). Ric. set. Mem. 17, 473.
Afzelius, B. A. (1956). Exp. Cell Res. 11, 67.
Afzelius, B. A. (1957a). Z. Zellforsch. 45, 660.
Afzelius, B. A. (1957b). 'Electron Microscopy on Sea-urchin Gametes', Almqvist
and Wiksells Boktryckeri AB, Uppsala.
Agrell, I. and Persson, H. (1956). Nature, Lond. 178, 1398.