Int. J. Dev. Biol. 40: 239 - 244 (1996)
© UPV/EHU Press

Localization of a high molecular weight form of DNA topoisomerase I in amphibian oocytes.

D Gebauer, C Mais, K Zinger, R Hock, B Lieb and U Scheer

Department of Cell and Developmental Biology, Theodor-Boveri-Institute (Biocenter), University of Würzburg, Germany.

ABSTRACT Xenopus oocytes express a 165 kDa variant of DNA topoisomerase I (topo I) as opposed to the canonical 110 kDa form of somatic cells (Richard and Bogenhagen, Dev. Biol. 146: 4-11, 1991). By immunofluorescence microscopy using variant-specific antibodies we show that this high molecular weight form is associated with lampbrush chromosome loops and the inner regions of the amplified nucleoli. Inhibition of topo I-activity by either Camptothecin-treatment or microinjection of neutralizing antibodies resulted in loop retraction and the condensation of chromosomes and amplified nucleoli. These data indicate that the oocyte-specific 165 kDa form of topo I is involved in transcriptional processes mediated by RNA polymerase I and II and is therefore functionally equivalent to the somatic cell 110 kDa counterpart.