Apical-basal polarity and cell-fate determinants are crucial for the cell fate and control of stem cell numbers. However, their interplay leading to a precise stem cell number remains unclear. Drosophila pupal intestinal stem cells (pISCs) asymmetrically divide, generating one apical ISC progenitor and one basal Prospero (Pros)⁺ enteroendocrine mother cell (EMC), followed by symmetric divisions of each daughter before adulthood, providing an ideal system to investigate the outcomes of polarity loss. Using lineage tracing and ex vivo live imaging, we identify an interlocked polarity regulation network precisely determining ISC number: Bazooka inhibits Pros accumulation by activating Notch signaling to maintain stem cell fate in pISC apical daughters. A threshold of Pros promotes differentiation to EMCs and avoids ISC-like cell fate, and over-threshold of Pros inhibits miranda expression to ensure symmetric divisions in pISC basal daughters. Our work suggests that a polarity-dependent threshold of a differentiation factor precisely controls stem cell number.

顶端-基底极性和细胞命运决定因素对于细胞命运和干细胞数量的控制至关重要。然而，它们之间的相互作用导致精确的干细胞数量仍不清楚。果蝇蛹肠干细胞 (pISC) 不对称分裂，产生一个顶端 ISC 祖细胞和一个基底 Prospero (Pros) ⁺肠内分泌母细胞 (EMC)，随后每个女儿在成年前对称分裂，为研究果蝇的结果提供了一个理想的系统极性损失。利用谱系追踪和离体活体成像，我们确定了一个精确确定 ISC 数量的互锁极性调节网络：Bazooka 通过激活 Notch 信号传导来抑制 Pros 积累，以维持 pISC 顶端子细胞的干细胞命运。Pros 的阈值促进分化为 EMC 并避免类似 ISC 的细胞命运，而 Pros 的阈值过高会抑制miranda表达，以确保 pISC 基底子细胞的对称分裂。我们的工作表明，分化因子的极性依赖性阈值精确控制干细胞数量。