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 highly mutated version of the chicken thyroid hormone receptor (TR) alpha, have so far exclusively been linked to dominant repression of the antimitogenic roles of TR and retinoic acid receptors. Here we show that when expressed in Xenopus oocytes v-ErbA induced ultrastructural changes characteristic of early and intermediate events of meiotic maturation by activating gene transcription. v-ErbA-induced maturation events 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 vitro-generated mutant of human TR, suggesting that v-ErbA can contribute to cell cycle reentry by interference with regulatory pathways distinct from those involving TR. Interestingly, a portion of v-ErbA expressed in oocytes was present at the cytoplasmic fibrils of the nuclear pore complexes, suggesting that in addition to its intranuclear function v-ErbA may modulate nucleocytoplasmic transport.