Fig 2 Data.

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.

基底膜（basement membrane, BM）在干细胞维持与活性调控中发挥关键作用。本研究证实，硫酸软骨素（chondroitin sulfate, CS）作为果蝇中肠基底膜的主要组分，对肠道干细胞（intestinal stem cells, ISCs）的正常调控必不可少。敲除CS的关键生物合成基因Chsy后，稳态条件下ISC增殖水平升高，引发中肠增生。再生实验表明，Chsy突变的ISC无法在再生结束时正常下调有丝分裂活性。我们还发现，CS对维持肠道上皮屏障完整性、防止肠上皮渗漏至关重要。已知CS可通过Chsy与另一关键蛋白软骨素聚合因子（chondroitin polymerizing factor, Chpf）组成的复合物完成聚合。我们发现，Chpf突变体在中肠稳态与再生过程中ISC分裂水平同样升高，表型与Chsy突变体一致。鉴于Chpf在再生过程中由组织损伤诱导，我们的实验数据表明，Chpf可与Chsy协同发挥功能，促进CS重塑并刺激组织修复。我们提出，含CS的基底膜修复完成是正常终止再生过程的先决条件。