The Drosophila pumilio Gene Encodes Two Functional Protein Isoforms That Play Multiple Roles in Germline Development, Gonadogenesis, Oogenesis and Embryogenesis

Corresponding author: Haifan Lin, Department of Cell Biology, Duke University Medical Center, Box 3709, 412 Nanaline Duke Bldg., Durham, NC 27710., h.lin{at}cellbio.duke.edu (E-mail)

Communicating editor: T. SCHÜPBACH

The pumilio (pum) gene plays an essential role in embryonic patterning and germline stem cell (GSC) maintenance during oogenesis in Drosophila. Here we report on a phenotypic analysis using pum^ovarette mutations, which reveals multiple functions of pum in primordial germ cell proliferation, larval ovary formation, GSC division, and subsequent oogenic processes, as well as in oviposition. Specifically, by inducing pum^- GSC clones at the onset of oogenesis, we show that pum is directly involved in GSC division, a function that is distinct from its requirement in primordial germ cells. Furthermore, we show that pum encodes 156- and 130-kD proteins, both of which are functional isoforms. Among pum^ovarette mutations, pum¹⁶⁸⁸ specifically eliminates the 156-kD isoform but not the 130-kD isoform, while pum²⁰⁰³ and pum⁴²⁷⁷ specifically affect the 130-kD isoform but not the 156-kD isoform. Normal doses of both isoforms are required for the zygotic function of pum, yet either isoform alone at a normal dose is sufficient for the maternal effect function of pum. A pum cDNA transgene that contains the known open reading frame encodes only the 156-kD isoform and rescues the phenotype of both pum¹⁶⁸⁸ and pum²⁰⁰³ mutants. These observations suggest that the 156- and 130-kD isoforms can compensate for each other's function in a dosage-dependent manner. Finally, we present molecular evidence suggesting that the two PUM isoforms share some of their primary structures.

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