Delivery of germinal granules and localized RNAs via the messenger transport organizer pathway to the vegetal cortex of Xenopus oocytes occurs through directional expansion of the mitochondrial cloud
Original Article | Published: 1 March 2005
Katarzyna Wilk1, Szczepan Bilinski1, Matthew T. Dougherty2 and Malgorzata Kloc*,3
1Institute of Zoology, Jagiellonian University, Krakow, Poland, 2Biomedical Computation and Visualization Laboratory, Baylor College of Medicine, National Center for Macromolecular Imaging, Houston, USA and 3Department of Molecular Genetics, The University of Texas, M.D. Anderson Cancer Center, Houston, USA
During Xenopusoogenesis, the message transport organizer (METRO) pathway delivers germinal granules and localized RNAs to the vegetal cortex of the oocyte via the mitochondrial cloud (Balbiani body). According to the traditional model, the mitochondrial cloud is thought to break up at the onset of vitellogenesis and the germinal granules and METRO-localized RNAs are transported within the mitochondrial cloud fragments to the vegetal cortex of the oocyte. We used light and electron microscopy in situhybridization and three-dimensional reconstruction to show that germinal granules and METRO-localized RNAs are delivered to the oocyte cortex before the onset of mitochondrial cloud fragmentation and that the delivery involves accumulation of localized RNAs and aggregation of germinal granules at the vegetal tip of the mitochondrial cloud and subsequent internal expansion of the mitochondrial cloud between its animal (nuclear) and vegetal tips, which drives the germinal granules and METRO-localized RNAs toward the vegetal cortex. Thus the fragmentation of the cloud that occurs later in oogenesis is irrelevant to the movement of METRO-localized RNAs and germinal granules. On the basis of these findings, we propose here a revised model of germinal granule and localized RNAs delivery to the oocyte vegetal cortex via the METRO pathway.
localized RNA, METRO pathway, mitochondrial cloud, Balbiani body, germinal granules