Expression of RNA polymerase I-specific transcription factors during early Xenopus development
Project leader: Ulrich Scheer (PI), Norbert Wilken (Co-PI)
Staff: J. Ulbrich (since 5/04); Claudia Rohner
Objectives: To understand molecular mechanisms involved in rRNA gene activation and nucleolar assembly during early amphibian development.
Approach: Due to a large stockpile of ribosomes stored in the egg, protein synthesis of preblastula Xenopus embryos is based entirely on ribosomes of maternal origin. Only after the midblastula transition, when the embryonic genome is being activated, typical nucleoli emerge by a stepwise process which, however, is poorly understood. To gain insight into the mechanisms causing transcriptional quiescence of the rRNA genes and nucleolar absence at preblastula stages, we have studied the expression and localization of the pol I transcription machinery in early embryos and "synthetic" nuclei assembled from sperm chromatin. In particular we have asked whether or not pol I and pol I-specific factors are already present in the cleavage embryo prior to gene activation and where they are located.
Progress: Presently our focus is on the transcription factor TAF63 which -together with other proteins- forms the multi-subunit transcription complex SL1. We have already determined the amino acid sequence of Xenopus TAF63 and could show by using RT-PCR that maternal transcripts are present in oocytes and throughout embryogenesis.
Significance: Our data should help to decipher the mechanisms leading to the sudden activation of a specific class of genes at the midblastula transition of Xenopus embryos..
Future projects: After raising specific antibodies we plan to examine the expression and localization of TAF63 during oogenesis and early embryogenesis in comparison with pol I and other transcription factors such as UBF.
Collaborations: Dr. Brian McStay and Dr. Christine Mais (Biomedical Research Centre, University of Dundee, Scotland).
Current external funding: None