Chondroitin sulfate regulates proliferation of Drosophila intestinal stem cells

The basement membrane (BM) plays critical roles in stem cell maintenance and activity control. Here we show that chondroitin sulfate (CS), a major component of the Drosophila midgut BM, is required for proper control of intestinal stem cells (ISCs). Loss of Chsy, a critical CS biosynthetic gene, resulted in elevated levels of ISC proliferation during homeostasis, leading to midgut hyperplasia. Regeneration assays demonstrated that Chsy mutant ISCs failed to properly downregulate mitotic activity at the end of regeneration. We also found that CS is essential for the barrier integrity to prevent leakage of the midgut epithelium. CS is known to be polymerized by the action of the complex of Chsy and another critical protein, Chondroitin polymerizing factor (Chpf). We found that Chpf mutants show increased ISC division during midgut homeostasis and regeneration, similar to Chsy mutants. As Chpf is induced by a tissue damage during regeneration, our data suggest that Chpf functions with Chsy to facilitate CS remodeling and stimulate tissue repair. We propose that the completion of the repair of CS-containing BM acts as a prerequisite to properly terminate the regeneration process.