Autoradiographic Evidence for the Association of DNA With Intracytoplasmic A-Particle Inclusions In Situ

Summary

Mice with subcutaneous transplants of a Leydig cell tumor were given tritiated thymidine sc proximal to the tumor mass. The labeled tissue was collected and samples for autoradiography were taken. Nuclei and intracytoplasmic A particle(s) (CAP), were purified from the remainder of the tumor pool. The distribution of radioisotopic grains over electron microscopic autoradiographs was semiquantitated and analyzed. Grains were found over CAP inclusions in situ. Comparison of the relative frequency of CAP-associated grains to nuclear grains by probability on a planar area basis revealed a higher frequency of thymidine incorporation into these structures. Isolation and comparison of the DNA(s) associated with CAP and nuclei showed a higher specific activity for CAP-associated DNA than for nuclear DNA, which was in good agreement with the autoradiographic analysis. The DNA associated with the purified CAP possessed a significantly higher buoyant density in CsCI than did the nuclear DNA. These results implied that this DNA was present in CAP inclusions in situ.