26
LEROY C. S T E V E N S
C. In Mammalian Fetuses
Testicular teratomas can be readily induced in inbred strain 129
(Stevens, 1965) and strain A/He mice. If genital ridges from fetal mice
are transplanted to the testis of adults, about 75% of the male ones
develop into testes with multifocal teratomas. There is a sharply defined
period of susceptibility for both strains. For strain 129, the primordial
germ cells become resistant to this experimental teratocarcinogenesis
during the thirteenth day of gestation. Apparently these cells undergo a
differentiation which prevents them from developing into teratomas.
There is a strong environmental influence involved; if 12.5-day genital
ridges are grafted to the spleen, for example, only 9% of them become
tumorous. Of many graft sites tested, only the testic, epididymis, and
testicular fat pad have been shown to exert this strong teratocarcinogenetic influence. The incidence of induced teratomas is much lower in
cryptorchid than in normally situated testes. In fact, in unilaterally
cryptorchidized animals, over twice as many teratomas are found in the
normal testis as in the contralateral cryptorchid testis (Stevens, unpublished). It is possible that the lower temperature of the normal testis
plays a role in teratocarcinogenesis. The high degree of repeatability of
experimental induction of teratomas in the mouse testis suggests that the
neoplastic change is not the result of a genetic mutation. It seems more
reasonable that the activity of the genes has been changed in the
environment provided by the adult testis.
XIV. Plant Teratomas
Braun (1965) experimentally induced teratomas from normal plant
cells, and subsequently transformed them to normal cells. The tumor
cells were multipotential with the capacity to heal themselves and
recover completely from the tumorous state. He grafted teratoma tissue
derived from single cells to the tips of cut stems of tobacco plants. The
neoplastic cells grew rapidly and organized abnormal leaves and buds.
These buds were removed and grafted to cut stem tips of tobacco plants
and the grafted buds grew slowly into abnormal shoots. The tumorous
shoots were allowed to grow, and their tips were removed and grafted
to another plant. When this procedure was repeated a third time, the
grafted tip usually developed into a normal shoot which was fertile and
gave rise to normal tobacco plants. Thus, the transformed tumor cells
made a complete recovery.
Hagen (1962) described techniques for changing hybrid tobacco tissues
from normal to teratomatous and then to amorphous growths and then
reversing the process. He concluded that the tumor cells were totipotent
and that the morphology of the cultured tumor can be a function of the
LEROY C. S T E V E N S
C. In Mammalian Fetuses
Testicular teratomas can be readily induced in inbred strain 129
(Stevens, 1965) and strain A/He mice. If genital ridges from fetal mice
are transplanted to the testis of adults, about 75% of the male ones
develop into testes with multifocal teratomas. There is a sharply defined
period of susceptibility for both strains. For strain 129, the primordial
germ cells become resistant to this experimental teratocarcinogenesis
during the thirteenth day of gestation. Apparently these cells undergo a
differentiation which prevents them from developing into teratomas.
There is a strong environmental influence involved; if 12.5-day genital
ridges are grafted to the spleen, for example, only 9% of them become
tumorous. Of many graft sites tested, only the testic, epididymis, and
testicular fat pad have been shown to exert this strong teratocarcinogenetic influence. The incidence of induced teratomas is much lower in
cryptorchid than in normally situated testes. In fact, in unilaterally
cryptorchidized animals, over twice as many teratomas are found in the
normal testis as in the contralateral cryptorchid testis (Stevens, unpublished). It is possible that the lower temperature of the normal testis
plays a role in teratocarcinogenesis. The high degree of repeatability of
experimental induction of teratomas in the mouse testis suggests that the
neoplastic change is not the result of a genetic mutation. It seems more
reasonable that the activity of the genes has been changed in the
environment provided by the adult testis.
XIV. Plant Teratomas
Braun (1965) experimentally induced teratomas from normal plant
cells, and subsequently transformed them to normal cells. The tumor
cells were multipotential with the capacity to heal themselves and
recover completely from the tumorous state. He grafted teratoma tissue
derived from single cells to the tips of cut stems of tobacco plants. The
neoplastic cells grew rapidly and organized abnormal leaves and buds.
These buds were removed and grafted to cut stem tips of tobacco plants
and the grafted buds grew slowly into abnormal shoots. The tumorous
shoots were allowed to grow, and their tips were removed and grafted
to another plant. When this procedure was repeated a third time, the
grafted tip usually developed into a normal shoot which was fertile and
gave rise to normal tobacco plants. Thus, the transformed tumor cells
made a complete recovery.
Hagen (1962) described techniques for changing hybrid tobacco tissues
from normal to teratomatous and then to amorphous growths and then
reversing the process. He concluded that the tumor cells were totipotent
and that the morphology of the cultured tumor can be a function of the