Structural responses of amoebae to the injection of heterologous cytoplasm

Responses to the introduction of heterologous cytoplasm and the fate of foreign organelles were investigated in amoebae. Heterologous cytoplasm was transferred by microinjection from Pelomyxa carolinensis to Amoeba discoides. In control experiments, homologous cytoplasm was transferred from one A. discoides to another. Recipient cells were observed by light microscopy, and samples were prepared for ultrastructural study at intervals between 15 min nad 3 days after operation. Recipients of heterologous cytoplasm showed two main responses. First, about 40% recipients expelled small amounts of cytoplasm by a blebbing process within 30 min after injection. Second, organelles were segregated and broken down in membrane-bounded cytoplasmic vacuoles between 6 h and 2 days after operation. Acid phosphatase reaction product was observed in these vacuoles along with altered organelles. Use of electron-dense thoria particles to mark donor cells demonstrated the presence of injected cytoplasm in the vacuoles. In contrast, when amoebae were injected with homologous cytoplasm, none was expelled and vacuoles containing degenerating organelles were uncommon. The survival rate and general appearance of recipients of heterologous cytoplasm were much poorer than those of homologous recipients, and most of the former died by I week after operation. It is postulated that amoeba are capable of recognizing heterologous organelles introduced into the cytoplasm and that they respond by expulsion and/or destruction of the foreign cellular components. The previously described lethal effect of heterologous cytoplasm was confirmed.