Several important events transpire in Xenopus oocytes that determine proper development during embryogenesis. Because there is no transcription during the rapid cell division cycles of early embryogenesis, the oocyte must stockpile large amounts of ribosomes to support the demands of protein synthesis during the period following fertilization. There are two types of genes that encode 5S ribosomal RNA. One, the somatic-type, is transcribed at all stages of development, while the other, the oocyte-type, is only transcribed during oogenesis and early embryogenesis. Thus, the differential expression of these genes provides a good model system for studying the developmental control of transcription. The principal regulator of 5S rRNA gene transcription is TFIIIA. We have found that this transcription factor becomes phosphorylated and SUMOylated at key times during development. These modifications apparently change the expression pattern of the 5S rRNA genes. The goal of this work is to understand these events at the molecular level.

The body plan of the frog begins to be determined in the unfertilized oocyte. The localization of some crucial mRNAs to specific regions of this single cell is a major mechanism that underlies proper development during embryogenesis. One mRNA, Vg1, encodes a member of the TGF-β family and is localized to the vegetal cortex of the mature oocyte. We have identified several proteins that bind to the region of Vg1 mRNA that determines its localization and translational control. Currently, our aim is to determine the role of each factor in localization, how these proteins interact and work together in this process, and to identify other components of the mRNA localization pathway.