Drosophila Stem Cells Share a Common Requirement for the Histone H2B Ubiquitin Protease Scrawny

Stem cells within diverse tissues share the need for a chromatin configuration that promotes self- renewal, yet few chromatin proteins are known to regulate multiple types of stem cells. We describe a Drosophila gene, scrawny ( scny), encoding a ubiquitin- specific protease, which is required in germline, epithelial, and intestinal stem cells. Like its yeast relative UBP10, Scrawny deubiquitylates histone H2B and functions in gene silencing. Consistent with previous studies of this conserved pathway of chromatin regulation, scny mutant cells have elevated levels of ubiquitinylated H2B and trimethylated H3K4. Our findings suggest that inhibiting H2B ubiquitylation through scny represents a common mechanism within stem cells that is used to repress the premature expression of key differentiation genes, including Notch target genes.