Special Issue Reviews–A Peer Reviewed Forum
Postplasmic/PEM RNAs: A class of localized maternal mRNAs with multiple roles in cell polarity and development in ascidian embryos
Article first published online: 15 MAR 2007
Copyright © 2007 Wiley-Liss, Inc.
Special Issue: Special Focus on Ciona
Volume 236, Issue 7, pages 1698–1715, July 2007
How to Cite
Prodon, F., Yamada, L., Shirae-Kurabayashi, M., Nakamura, Y. and Sasakura, Y. (2007), Postplasmic/PEM RNAs: A class of localized maternal mRNAs with multiple roles in cell polarity and development in ascidian embryos. Dev. Dyn., 236: 1698–1715. doi: 10.1002/dvdy.21109
- Issue published online: 18 JUN 2007
- Article first published online: 15 MAR 2007
- Manuscript Accepted: 5 FEB 2007
- JSPS (Japan Society for the Promotion of Science)
- maternal mRNA;
- posterior pole;
- unequal cleavage;
Ascidian is a good model to understand the cellular and molecular mechanisms responsible for mRNA localization with the discovery of a large family of localized maternal mRNAs, called postplasmic/PEM RNAs, which includes more than 40 members in three different ascidian species (Halocynthia roretzi, Ciona intestinalis, and C. savignyi). Among these mRNAs, two types (Type I and Type II) have been identified and show two different localization patterns from fertilization to the eight-cell stage. At the eight-cell stage, both types concentrate to a macromolecular cortical structure called CAB (for Centrosome Attracting Body) in the posterior-vegetal B4.1 blastomeres. The CAB is responsible for unequal cleavages and the partitioning of postplasmic/PEM RNAs at the posterior pole of embryos during cleavage stages. It has also been suggested that the CAB region could contain putative germ granules. In this review, we discuss recent data obtained on the distribution of Type I postplasmic/PEM RNAs from oogenesis to late development, in relation to their localization and translational control. We have first regrouped localization patterns for Type I and Type II into a comparative diagram and included all important definitions in the field. We also have made an exhaustive classification of their embryonic expression profiles (Type I or Type II), and analyzed their functions after knockdown and/or overexpression experiments and the role of the 3′-untranslated region (3′UTR) controlling both their localization and translation. Finally, we propose a speculative model integrating recent data, and we also discuss the relationship between postplasmic/PEM RNAs, posterior specification, and germ cell formation in ascidians. Developmental Dynamics 236:1698–1715, 2007. © 2007 Wiley-Liss, Inc.