TRANSPLANTATION OF CELL NUCLEI
19
intestine cell nuclei promote normal development after transplantation
than do blastula nuclei. However, there are many possible explanations
for this, such as the infrequent division of differentiated cells, which
could account for the nuclei of these cells not being prepared for
division immediately after transfer. It is therefore not necessary to
assume that a restrictive change has taken place in these nuclei. The
results of transplanting Xenopus intestine nuclei and Rana adenocarcinoma nuclei clearly show that stable changes restricting the
developmental capacity of nuclei cannot always be essential for cell
differentiation to take place.
Adult transplant frogs
We have so far discussed only those nuclear changes revealed in
transplant-embryo development. There may however be genes whose
function is manifested only in adult characters such as reproductive
capacity, and stable changes in these genes would only be shown by a
study of adult transplant-frogs. A detailed study has been made of over
150 adult Xenopus derived from nuclei of donor embryos ranging from
blastulae to swimming tadpoles (Gurdon, 1962a). The frogs of advanceddonor origin (hatched and swimming tadpoles) did not differ significantly from the frogs of early-donor origin (embryonic and larval stages
up to hatching) in any respect except in reproductive capacity. None
out of 125 of the early-donor frogs but seven out of twenty-seven of the
advanced-donor frogs were sterile. The remaining twenty advanceddonor frogs produced normal gametes. These fertile males and females
clearly show that nuclei of hatched tadpole endoderm cells can promote
the formation of every other cell type. They incidentally show that the
normal differentiation of gametes does not depend upon the permanent
association of germ-plasm with germ-line nuclei since hatched tadpole
endoderm cells have been devoid of germ-plasm for several divisions
(Gurdon, 1962a). Recently ten frogs derived from transplanted intestinal epithelium cell nuclei of feeding tadpoles have become adult. These
do not differ from blastula transplant frogs except in reproductive
capacity. Though some of these frogs are normally fertile, too many are
sterile to attribute this to the accumulation of spontaneous mutations.
We are therefore forced to conclude that nuclear changes resulting in
sterility take place either in connection with cell differentiation or more
likely as a result of transplantation, especially of nuclei from advanced
donors.
Conclusions
This discussion can be summarized as follows. There is complete
agreement from all nuclear transfer experiments that transplanted
19
intestine cell nuclei promote normal development after transplantation
than do blastula nuclei. However, there are many possible explanations
for this, such as the infrequent division of differentiated cells, which
could account for the nuclei of these cells not being prepared for
division immediately after transfer. It is therefore not necessary to
assume that a restrictive change has taken place in these nuclei. The
results of transplanting Xenopus intestine nuclei and Rana adenocarcinoma nuclei clearly show that stable changes restricting the
developmental capacity of nuclei cannot always be essential for cell
differentiation to take place.
Adult transplant frogs
We have so far discussed only those nuclear changes revealed in
transplant-embryo development. There may however be genes whose
function is manifested only in adult characters such as reproductive
capacity, and stable changes in these genes would only be shown by a
study of adult transplant-frogs. A detailed study has been made of over
150 adult Xenopus derived from nuclei of donor embryos ranging from
blastulae to swimming tadpoles (Gurdon, 1962a). The frogs of advanceddonor origin (hatched and swimming tadpoles) did not differ significantly from the frogs of early-donor origin (embryonic and larval stages
up to hatching) in any respect except in reproductive capacity. None
out of 125 of the early-donor frogs but seven out of twenty-seven of the
advanced-donor frogs were sterile. The remaining twenty advanceddonor frogs produced normal gametes. These fertile males and females
clearly show that nuclei of hatched tadpole endoderm cells can promote
the formation of every other cell type. They incidentally show that the
normal differentiation of gametes does not depend upon the permanent
association of germ-plasm with germ-line nuclei since hatched tadpole
endoderm cells have been devoid of germ-plasm for several divisions
(Gurdon, 1962a). Recently ten frogs derived from transplanted intestinal epithelium cell nuclei of feeding tadpoles have become adult. These
do not differ from blastula transplant frogs except in reproductive
capacity. Though some of these frogs are normally fertile, too many are
sterile to attribute this to the accumulation of spontaneous mutations.
We are therefore forced to conclude that nuclear changes resulting in
sterility take place either in connection with cell differentiation or more
likely as a result of transplantation, especially of nuclei from advanced
donors.
Conclusions
This discussion can be summarized as follows. There is complete
agreement from all nuclear transfer experiments that transplanted