Embryology of Testicular Teratomas in Strain 129 Mice2

Abstract

Based on observations of teratomas in strain 129 infant mice, the following sequence of development is proposed: The most primitive tumors are composed of clusters of embryonal cells with germ cells interspersed. Some of these cells form epithelial vesicles surrounding pools of blood and cellular debris. Approximately half these vesicles are morphologically different from the other half, signifying the formation of layers of cells homologous to ectoderm and endoderm. Mesoderm surrounds the vesicles. Ectoderm is transformed into neuroepithelium; teratomatous endoderm gives rise to alimentary and respiratory epithelium; and mesoderm becomes muscle and cartilage. Embryoid bodies with inverted germ layers are observed in enormous numbers in ascitic fluid resulting from intraperitoneal grafts of transplantable teratomas. The endoderm in these formations resembles that in 6-day-old mouse embryos. The endoderm of the early primary tumors is similar to alimentary epithelium in 9-day-old embryos. Apparently the environment, whether fluid or cellular, exerts an important influence on the configuration of endodermal cells. The arrangement of endodermal cells in embryoid bodies indicates that they have centrifugal migration tendencies, which may explain, tentatively, the inversion of the germ layers in mouse embryos. In most of the early teratomas there is direct continuity between the germinal epithelium and teratomatous elements. This suggests, but is not critical proof, that testicular teratomas originate within the tubules of the fetal mouse testis.