Direct inhibition of Pumilo activity by Bam and Bgcn in Drosophila germ line stem cell differentiation.
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.
Kim
Ji Young
JY
Hormone Research Center, School of Biological Sciences and Technology, Chonnam National University, Gwangju 500-757, South Korea.
Lee
Young Chul
YC
Kim
Changsoo
C
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
D029721:Drosophila Proteins; D016601:RNA-Binding Proteins; C091674:bam protein, Drosophila; C074333:pum protein, Drosophila; D004265:DNA Helicases; C414082:bgcn protein, Drosophila