190
R. LALLIER
Among the synthetic processes studied in the sea urchin egg a
significant place has been given to the study of nucleic acids and
proteins. This orientation of the research is justified by the important
functions of these cellular constituents and by the fundamental role of
the nucleic acids in protein synthesis. However, we should mention that
lipids enter appreciably into the constitution of cellular structures and
their role in cellular differentiation must not be underestimated. A study
of them will help to make our knowledge of the processes of differentiation more precise.
Autoradiographic methods have contributed a great deal to the
analysis of synthetic processes. Regional differences in the incorporation
of the labelled precursors of nucleic acids and proteins have been
observed at different stages of development. In general, these researches
are still in their infancy. They must necessarily be completed by a
systematic study of the regional distribution of the incorporation of
labelled precursors into embryos animalized and vegetalized in different
ways. Finally, it is important to determine whether the uptake of
labelled molecules is due to synthesis or to turnover.
Another approach to the problem of differentiation lies in studying
the effects of various agents capable of interfering with the metabolism
of nucleic acids and proteins and comparing their effects on development
with those caused by animalizing and vegetalizing agents. The analogues
of natural precursors of nucleic acids and proteins are known to be
incorporated into these molecules without inhibiting their synthesis.
From the results obtained, it follows that, as a rule, the analogues of
natural precursors such as nitrogenous bases and amino-acids, exert an
irregular and fairly weak action on the determination of the sea urchin
egg. These results contrast with the typical and constant effects of
vegetalizing and animalizing agents. It is an interesting fact that
chloramphenicol, which is an inhibitor of protein synthesis, exerts a
strong vegetalizing action. This observation suggests the existence of
differences of sensitivity in protein synthesis between the animal and
the vegetal parts of the egg. These differences may be due to functional
and structural peculiarities localized at the animal and vegetal pole of
the egg.
During the development of the sea urchin egg, metabolic activity
appears to be distributed in gradients. Reduction gradients have been
made visible. These gradients show great similarities to the animal and
vegetal morphogenetic gradients demonstrated by the transplantation
and isolation of blastomeres. A relationship may exist between these
gradients and the reducing activity of the mitochondria. However,
cytological observations reveal uniform distribution of mitochondria.
Differences in the enzymatic activity of the mitochondria may explain
R. LALLIER
Among the synthetic processes studied in the sea urchin egg a
significant place has been given to the study of nucleic acids and
proteins. This orientation of the research is justified by the important
functions of these cellular constituents and by the fundamental role of
the nucleic acids in protein synthesis. However, we should mention that
lipids enter appreciably into the constitution of cellular structures and
their role in cellular differentiation must not be underestimated. A study
of them will help to make our knowledge of the processes of differentiation more precise.
Autoradiographic methods have contributed a great deal to the
analysis of synthetic processes. Regional differences in the incorporation
of the labelled precursors of nucleic acids and proteins have been
observed at different stages of development. In general, these researches
are still in their infancy. They must necessarily be completed by a
systematic study of the regional distribution of the incorporation of
labelled precursors into embryos animalized and vegetalized in different
ways. Finally, it is important to determine whether the uptake of
labelled molecules is due to synthesis or to turnover.
Another approach to the problem of differentiation lies in studying
the effects of various agents capable of interfering with the metabolism
of nucleic acids and proteins and comparing their effects on development
with those caused by animalizing and vegetalizing agents. The analogues
of natural precursors of nucleic acids and proteins are known to be
incorporated into these molecules without inhibiting their synthesis.
From the results obtained, it follows that, as a rule, the analogues of
natural precursors such as nitrogenous bases and amino-acids, exert an
irregular and fairly weak action on the determination of the sea urchin
egg. These results contrast with the typical and constant effects of
vegetalizing and animalizing agents. It is an interesting fact that
chloramphenicol, which is an inhibitor of protein synthesis, exerts a
strong vegetalizing action. This observation suggests the existence of
differences of sensitivity in protein synthesis between the animal and
the vegetal parts of the egg. These differences may be due to functional
and structural peculiarities localized at the animal and vegetal pole of
the egg.
During the development of the sea urchin egg, metabolic activity
appears to be distributed in gradients. Reduction gradients have been
made visible. These gradients show great similarities to the animal and
vegetal morphogenetic gradients demonstrated by the transplantation
and isolation of blastomeres. A relationship may exist between these
gradients and the reducing activity of the mitochondria. However,
cytological observations reveal uniform distribution of mitochondria.
Differences in the enzymatic activity of the mitochondria may explain