128
ALBERTO MONROY AND RACHELE MAGGIO
The interesting point is that now the same result can be obtained by an
irradiation applied 8 minutes after fertilization, whereas no effect is
obtained when unfertilized eggs or sperm are irradiated with as much as
2,500 r. This experiment shows that in Drosophila, fertilization brings
about the activation of at least one gene, the su-er, on the activity of
which the morphogenesis of an organ of much later appearance depends.
In any case, taking Neyfakh's data at their face value, the onset of the
first period of nuclear control of morphogenesis is seen to coincide with
the onset of the stationary phase of respiration, while the second period
of nuclear control begins at the onset of the mesenchyme blastula stage.
On the other hand the fact that in the sea urchin embryo protein
synthesis appears to begin very soon after fertilization implies that the
nucleus must also be functioning to produce the appropriate messenger
RNA. The previously quoted results by Ficq et dl. (personal communication) do in fact prove the existence of a metabolically active nuclear
RNA from the early cleavage stages. It would be very interesting to
extend these investigations, as well as those on protein metabolism, to
embryos irradiated by the technique of Neyfakh.
The problem of nuclear differentiation in the course of development
has been subjected to intensive analysis following the early and wellknown nuclear transplantation experiments of Briggs and King (summarized in 1959) on amphibians. Similar experiments on the eggs of
other animals and in particular of sea urchins would be of great value
and extremely welcome, although they are admittedly much more
difficult to carry out. The observations of Lison and Pasteels (1951)
supplied interesting data showing a different DNA content in the nuclei
of the different cell lines beginning as early as the fourth cleavage.
Relevant differences were also observed among the nuclei of the various
territories. Among others, a very low DNA content was found in the
cells of the primary mesenchyme which, as was mentioned earlier, in
pulse experiments also showed the lowest incorporation of radioactive
amino-acids (Bosco and Monroy, 1962). The previously quoted experiments of Markman (1961a) in which
14
C-adenine was used as a precursor,
indicate that in the blastula stage incorporation is stronger in the nuclei
of the animal half whereas in the gastrula the situation appears to be
reversed and the stronger incorporation is found in the invaginating
endomesoderm. However, the material available on autoradiographic
experiments is at present too limited to allow one to form a definite
opinion and draw conclusions as to nuclear activities in the various
territories and stages of development. In particular it seems mandatory
to use more than one precursor. By way of an example, the observation
of Reverberi et al. (1960) may be quoted. It was found in the ascidians
that, while the incorporation of
14
C-adenine in the nuclei begins only at
ALBERTO MONROY AND RACHELE MAGGIO
The interesting point is that now the same result can be obtained by an
irradiation applied 8 minutes after fertilization, whereas no effect is
obtained when unfertilized eggs or sperm are irradiated with as much as
2,500 r. This experiment shows that in Drosophila, fertilization brings
about the activation of at least one gene, the su-er, on the activity of
which the morphogenesis of an organ of much later appearance depends.
In any case, taking Neyfakh's data at their face value, the onset of the
first period of nuclear control of morphogenesis is seen to coincide with
the onset of the stationary phase of respiration, while the second period
of nuclear control begins at the onset of the mesenchyme blastula stage.
On the other hand the fact that in the sea urchin embryo protein
synthesis appears to begin very soon after fertilization implies that the
nucleus must also be functioning to produce the appropriate messenger
RNA. The previously quoted results by Ficq et dl. (personal communication) do in fact prove the existence of a metabolically active nuclear
RNA from the early cleavage stages. It would be very interesting to
extend these investigations, as well as those on protein metabolism, to
embryos irradiated by the technique of Neyfakh.
The problem of nuclear differentiation in the course of development
has been subjected to intensive analysis following the early and wellknown nuclear transplantation experiments of Briggs and King (summarized in 1959) on amphibians. Similar experiments on the eggs of
other animals and in particular of sea urchins would be of great value
and extremely welcome, although they are admittedly much more
difficult to carry out. The observations of Lison and Pasteels (1951)
supplied interesting data showing a different DNA content in the nuclei
of the different cell lines beginning as early as the fourth cleavage.
Relevant differences were also observed among the nuclei of the various
territories. Among others, a very low DNA content was found in the
cells of the primary mesenchyme which, as was mentioned earlier, in
pulse experiments also showed the lowest incorporation of radioactive
amino-acids (Bosco and Monroy, 1962). The previously quoted experiments of Markman (1961a) in which
14
C-adenine was used as a precursor,
indicate that in the blastula stage incorporation is stronger in the nuclei
of the animal half whereas in the gastrula the situation appears to be
reversed and the stronger incorporation is found in the invaginating
endomesoderm. However, the material available on autoradiographic
experiments is at present too limited to allow one to form a definite
opinion and draw conclusions as to nuclear activities in the various
territories and stages of development. In particular it seems mandatory
to use more than one precursor. By way of an example, the observation
of Reverberi et al. (1960) may be quoted. It was found in the ascidians
that, while the incorporation of
14
C-adenine in the nuclei begins only at