A MONOCLONAL-ANTIBODY AGAINST DNA TOPOISOMERASE-II LABELS THE AXIAL GRANULES OF PLEURODELES LAMPBRUSH CHROMOSOMES

By immunizing Balb/c mice with oocyte nuclei of Pleurodeles waltl we o btained a monoclonal antibody, mAb 4A6, that labels distinct globular domains of the lampbrush chromosomal axes of Pleurodeles. These domain s are found at corresponding sites of homologous chromosomes, often at telomeric and putative centromeric regions, and appear to be devoid o f DNA. Because of these characteristic features it is most likely that the mAb 4A6-positive domains correspond to the central part of the '' axial granules'' of urodelan lampbrush chromosomes. In immunoblotting analyses mAb 4A6 reacts with a nuclear antigen of similar to M(r) 1800 00 and a structurally nonrelated cytoplasmic protein of M(r) 98000, wh ich was not characterized any further. Comparative immunofluorescence and immunoblotting studies with mAb 4A6 and an antiserum against DNA t opoisomerase II (topo II) as well as immunodepletion experiments demon strated that the nuclear 4A6 antigen is topo II. Our results indicate that topo II is not a constituent of a continuous, loop-anchoring scaf fold in lampbrush chromosomes of Pleurodeles but, rather, is restricte d to the axial granules.