Fate of herpesvirus DNA in embryos and tadpoles cloned from Lucké renal carcinoma nuclei

The Lucké renal carcinoma of the northern leopard frog, Rana pipiens, has a herpesvirus aetiology. Lucké tumour nuclei inserted into enucleated frogs' eggs produce development to the swimming tadpole stage. Tissue from these tumour nuclear transplant animals can be induced to survive and differentiate further by allografting to normal tadpoles. We wished to ascertain whether the aetiological agent, the Lucké tumour herpesvirus (LTV), persists in the animals produced by tumour nuclear transplantation. The polymerase chain reaction was used to amplify a 1·2 kbp Hind III restriction fragment of LTV DNA in whole animal homogenates prepared from tumour nuclear transplant tadpoles and normal tadpoles fertilized in vitro. The LTV fragment was not present in the majority (31 of 34) of the cloned animals derived from tumour nuclei, nor was it present in any of five normal tadpoles. Either the 1·2 kbp fragment of LTV DNA was eliminated from most of the cloned animals during the massive reprogramming of the neoplastic genome initiated by insertion of the tumour nuclei into egg cytoplasm, or the nuclei selected for transplantation were primarily those lacking this fragment of LTV DNA. The limited development of the tumour nuclear tadpoles was probably not due to the presence of these viral sequences, but rather reflected the limited plasticity of the tumour cell genome as assayed by nuclear transplantation. Failure to detect the 1·2 kbp fragment of LTV DNA in the majority of mitotic progeny of the Lucké tumour genome does not imply that other parts of the viral genome do not persist. The determination of which parts of the LTV genome are required for tumorigenesis awaits further research. The procedures used in this study can be exploited to evaluate which LTV sequences associated with oncogenesis are silenced during the normal differentiation process.