Cellular Functions of Nopp140 Splice Variants in Drosophila

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The primary function of the cell nucleolus is to assemble ribosomes that subsequently move from the nucleus to the cytoplasm, where they catalyze the synthesis of the cell's various proteins. Ribosome assembly is a complex series of biosynthetic reactions that begins at the gene level and ends with synthetically functional ribosomes, each of which consists of four RNA molecules and 80 different proteins. Ribosome assembly is thus a comprehensive paradigm for gene expression. Disruption of ribosome biosynthesis leads to lethality or developmental abnormalities. The goals of this research project are to establish a molecular-genetic approach toward understanding how nucleolar-specific proteins help assemble ribosomes in multicellular organisms. This project examines the functions of two closely-related nucleolar proteins in the fruitfly Drosophila melanogaster. Both proteins are encoded by the same gene, but the transcripts are processed differently in Drosophila cells, resulting in two protein variants. One of the two variants is very similar to a vertebrate nucleolar protein of unknown function called Nopp140. The other Drosophila variant is unique; it differs from all known vertebrate Nopp140 proteins in that the normal tail end of Nopp140 is replaced by a peptide domain found in many RNA-binding proteins. The project will define the developmental and tissue-specific expression patterns of the two Drosophila Nopp140 variants. Transgenic techniques will also be used to construct mutant flies with disruptions in either one or both Nopp140 variants. The effects of Nopp140 gene disruptions will be assessed by a combination of cytological and biochemical techniques.The project will involve both undergraduate and graduate students, and special effort will be made to recruit minority students to the project. In the course of this research, students will gain experience in modern genetics, cytology and biochemistry.