title: Direct inhibition of Pumilo activity by Bam and Bgcn in Drosophila germ line stem cell differentiation.
abstract: The fate of stem cells is intricately regulated by numerous extrinsic and intrinsic factors that promote maintenance or differentiation. The RNA-binding translational repressor Pumilio (Pum) in conjunction with Nanos (Nos) is required for self-renewal, whereas Bam (bag-of-marbles) and Bgcn (benign gonial cell neoplasm) promote differentiation of germ line stem cells in the Drosophila ovary. Genetic analysis suggests that Bam and Bgcn antagonize Pum/Nos function to promote differentiation; however, the molecular basis of this epistatic relationship is currently unknown. Here, we show that Bam and Bgcn inhibit Pum function through direct binding. We identified a ternary complex involving Bam, Bgcn, and Pum in which Bam, but not Bgcn, directly interacts with Pum, and this interaction is greatly increased by the presence of Bgcn. In a heterologous reporter assay to monitor Pum activity, Bam, but not Bgcn, inhibits Pum activity. Notably, the N-terminal region of Pum, which lacks the C-terminal RNA-binding Puf domain, mediates both the ternary protein interaction and the Bam inhibition of Pum function. These studies suggest that, in cystoblasts, Bam and Bgcn may directly inhibit Pum/Nos activity to promote differentiation of germ line stem cells.
authors.affiliation: Hormone Research Center, School of Biological Sciences and Technology, Chonnam National University, Gwangju 500-757, South Korea.
authors.forename: Ji Young
authors.initials: JY
authors.lastname: Kim
authors.forename: Young Chul
authors.initials: YC
authors.lastname: Lee
authors.forename: Changsoo
authors.initials: C
authors.lastname: Kim
mesh_terms: D000818:Animals; D002454:Cell Differentiation / Q000235:genetics / Q000502:physiology*; D002460:Cell Line; D004265:DNA Helicases / Q000235:genetics / Q000378:metabolism*; D004330:Drosophila; D029721:Drosophila Proteins / Q000235:genetics / Q000378:metabolism*; D005854:Germ Cells; D047468:Immunoprecipitation; D011485:Protein Binding / Q000235:genetics / Q000502:physiology; D016601:RNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D013234:Stem Cells / Q000166:cytology* / Q000378:metabolism*; D020798:Two-Hybrid System Techniques
chemical_list: D029721:Drosophila Proteins; D016601:RNA-Binding Proteins; C091674:bam protein, Drosophila; C074333:pum protein, Drosophila; D004265:DNA Helicases; C414082:bgcn protein, Drosophila