148
HERMAN DENIS
Enzymes able to transform one DNA base into another have been
described in sea urchin embryos and the activity of these enzymes
changes during development. It should be, however, emphasized that
Scarano and Augusti-Tocco's theory is in contradiction with Gurdon's
results (1962), which show that the nucleus of a differentiated cell is
totipotent, i.e., is able to support the development of a normal embryo,
when injected into an anucleate egg. Furthermore, the theory of Scarano
et al. is not easily amenable to experimental verifications since the
proposed modifications are likely to affect restricted regions of the DNA
and, hence, must be hard to detect.
The mechanism that controls DNA transcription in embryonic development is, thus, far from being elucidated. By studying the synthesis of
messenger RNA during the differentiation process, we have described
the effects of this mechanism without elucidating or even identifying it.
Our knowledge in this field will not really progress so long as we are
unable to explain how the expression of the genome is controlled by the
cytoplasm, for all the interactions that determine the fate of each region
of the early embryo are primarily cytoplasmic events.
Acknowledgment
I wish to thank Dr. P. Malpoix for improving the English version of the
manuscript.
References
Attardi, G., Huang, P. C, and Kabat, S. (1965). Proc. Natl. Acad. Sci. U.S. 53, 1490.
Attardi, G., Parnas, H., Hwang, M. I. H., and Attardi, B. (1966).
Mol. Biol. 20,
145.
Barr, G. C., and Butler, J. A. V. (1963). Nature 199, 1170.
Bloch, D. P. (1962). Proc. Natl. Acad. Sci. U.S. 48, 324.
Bolton, E. T., and MacCarthy, B. J. (1962). Proc. Natl. Acad. Sci. U.S. 48, 1390.
Brachet, J. (1967). In "Comprehensive Biochemistry" (M. Florkin and E. H. Stotz,
eds.), Vol. 28. Elsevier, Amsterdam.
Brown, D. D., and Gurdon, J. (1964). Proc. Natl. Acad. Sci. U.S. 51, 139.
Brown, D. D., and Gurdon, J. (1966). /. Mol. Biol 19, 399.
Brown, D. D., and Littna, E. (1964a). J. Mol Biol. 8, 669.
Brown, D. D., and Littna, E. (1964b). /. Mol Biol. 8, 688.
Brown, D. D., and Littna, E. (1966a). /. Mol. Biol. 20, 81.
Brown, D. D., and Littna, E. (1966b). /. Mol Biol 20, 95.
Cohen, S. (1954). /. Biol. Chem. 211, 337.
Davidson, E. H., Crippa, M., Kramer, F. R., and Mirsky, A. E. (1966). Proc. Natl
Acad. Sci. U.S. 56, 856.
Dawid, I. B. (1965). /. Mol. Biol. 12, 581.
Denis, H. (1964a). Develop. Biol. 9, 435.
HERMAN DENIS
Enzymes able to transform one DNA base into another have been
described in sea urchin embryos and the activity of these enzymes
changes during development. It should be, however, emphasized that
Scarano and Augusti-Tocco's theory is in contradiction with Gurdon's
results (1962), which show that the nucleus of a differentiated cell is
totipotent, i.e., is able to support the development of a normal embryo,
when injected into an anucleate egg. Furthermore, the theory of Scarano
et al. is not easily amenable to experimental verifications since the
proposed modifications are likely to affect restricted regions of the DNA
and, hence, must be hard to detect.
The mechanism that controls DNA transcription in embryonic development is, thus, far from being elucidated. By studying the synthesis of
messenger RNA during the differentiation process, we have described
the effects of this mechanism without elucidating or even identifying it.
Our knowledge in this field will not really progress so long as we are
unable to explain how the expression of the genome is controlled by the
cytoplasm, for all the interactions that determine the fate of each region
of the early embryo are primarily cytoplasmic events.
Acknowledgment
I wish to thank Dr. P. Malpoix for improving the English version of the
manuscript.
References
Attardi, G., Huang, P. C, and Kabat, S. (1965). Proc. Natl. Acad. Sci. U.S. 53, 1490.
Attardi, G., Parnas, H., Hwang, M. I. H., and Attardi, B. (1966).
Mol. Biol. 20,
145.
Barr, G. C., and Butler, J. A. V. (1963). Nature 199, 1170.
Bloch, D. P. (1962). Proc. Natl. Acad. Sci. U.S. 48, 324.
Bolton, E. T., and MacCarthy, B. J. (1962). Proc. Natl. Acad. Sci. U.S. 48, 1390.
Brachet, J. (1967). In "Comprehensive Biochemistry" (M. Florkin and E. H. Stotz,
eds.), Vol. 28. Elsevier, Amsterdam.
Brown, D. D., and Gurdon, J. (1964). Proc. Natl. Acad. Sci. U.S. 51, 139.
Brown, D. D., and Gurdon, J. (1966). /. Mol. Biol 19, 399.
Brown, D. D., and Littna, E. (1964a). J. Mol Biol. 8, 669.
Brown, D. D., and Littna, E. (1964b). /. Mol Biol. 8, 688.
Brown, D. D., and Littna, E. (1966a). /. Mol. Biol. 20, 81.
Brown, D. D., and Littna, E. (1966b). /. Mol Biol 20, 95.
Cohen, S. (1954). /. Biol. Chem. 211, 337.
Davidson, E. H., Crippa, M., Kramer, F. R., and Mirsky, A. E. (1966). Proc. Natl
Acad. Sci. U.S. 56, 856.
Dawid, I. B. (1965). /. Mol. Biol. 12, 581.
Denis, H. (1964a). Develop. Biol. 9, 435.