Transmission electron microscopy of malignant neurogenic rat cells during invasion into embryonic chick heart fragments in vitro.

Invasion of chemically induced brain tumour cells from BD IX-rats into precultured fragments of embryonic chick heart (PHF) was studied by transmission electron microscopy. The malignant cells from monolayer cultures were suspended and allowed to form aggregates for 24 hours on a gyratory shaker. The single aggregates were allowed ro attach to a single PHF and thereafter incubated in a confronting culture on a gyratory shaker. Invasion into the PHF started with cytoplasmic cell extensions between PHF cells and vanishing of heart cell junctions. Irreversible intracellular alterations in heart cells followed the disruption of intracellular contact by the malignant neurogenic cells. The latter exhibited fewer microvilli when invading the PHF than when located at the periphery. No junctions connecting heart cells with neurogenic cells were observed. Malignant cells were lying between the PHF and no extensions were seen in PHF cells. Hetero/autophagosomes were regularly present in the malignant cells and also in PHF cells. The aggregates of the 13 tumourigenic neurogenic cell lines tested, all produced the same alterations in the PHF cells.