Regulation of Maternal mRNA in Early Development by Translation and Localisation
Gene expression in early development, at a time when transcription is silent, is essentially regulated at the level of protein synthesis, in a wide variety of organisms.
In Xenopus, when oocytes resume meiosis, specific mRNAs are recruited onto polysomes from a quiescent form. These masked mRNAs encode polypeptides necessary for cell cycle entry and progression, such as c-mos and cyclin B1 mRNAs, and are translationally regulated by CPEB. In oocytes CPEB is present in a very large, P-body like RNP complex, which contains several other RNA-binding proteins including Xp54 RNA helicase, Pat1 and RAP55, as well as an ovary-specific eIF4E cap-binding protein and 4E-T (1). The temporal and spatial regulation of maternal mRNAs also establishes embryonic axes and determines cell fate. One example of a localised Xenopus mRNA, subject to translational control, is Vg1 mRNA (2), which encodes a member of the transforming growth factor β family. Current projects focus on characterising the role of components of the CPEB complex in translational repression, and on identifying small non-coding RNAs including microRNAs in Xenopus oocytes (3). We are also interested in identifying and characterising components of the RNA transport and anchoring machinary, including Vg1RBP and Staufen, and in analysing the link between RNA localisation and translational control of Vg1 mRNA.