V-ERBA ONCOGENE INITIATES ULTRASTRUCTURAL-CHANGES CHARACTERISTIC OF EARLY AND INTERMEDIATE EVENTS OF MEIOTIC MATURATION IN XENOPUS OOCYTES

The growth-promoting properties of the retroviral v-erbA oncogene, a h ighly mutated version of the chicken thyroid hormone receptor (TR) alp ha, have so far exclusively been linked to dominant repression of the antimitogenic roles of TR and retinoic acid receptors. Here we show th at when expressed in Xenopus oocytes v-ErbA induced ultrastructural ch anges characteristic of early and intermediate events of meiotic matur ation by activating gene transcription. v-ErbA-induced maturation even ts occurred without activation of the cAMP/maturation-promoting factor signal pathway and were arrested prior to meiotic spindle formation. The effects of v-ErbA were not mimicked by a dominant negative in vitr o-generated mutant of human TR, suggesting that v-ErbA can contribute to cell cycle reentry by interference with regulatory pathways distinc t from those involving TR. Interestingly, a portion of v-ErbA expresse d in oocytes was present at the cytoplasmic fibrils of the nuclear por e complexes, suggesting that in addition to its intranuclear function v-ErbA may modulate nucleocytoplasmic transport. (C) 1997 Wiley-Liss, Inc.