发育过程中的干细胞数目决定问题是理解组织稳态平衡、癌症，衰老等重大问题的关键。果蝇蛹期600个肠道干细胞前体细胞先不对称分裂，后各自对称分裂，产生一对干细胞与一对内分泌细胞，出蛹前达到1200个干细胞。我们发现不对称分裂时,细胞极性蛋白Mira通过物理结合将内分泌细胞分化因子Pros定位到子代细胞中；而内分泌细胞对称分裂时，Mira表达消失，Pros分布于两个子代细胞。于是我们猜测Mira是决定干细胞数目的关键因子。令人惊讶的是，当我们额外表达Mira时，干细胞数目增加一倍，内分泌细胞数目不变。更加有趣的是，敲除Mira，干细胞的数目同样增加一倍。前期结果显示，Mira通过控制Pros的阈值性分布精确调控肠道干细胞的数目。我们申请通过进一步的细胞、遗传、分子、筛选等实验，进一步挖掘其背后的分子机制，建立以果蝇肠道干细胞不对称分裂为研究范式的干细胞命运决定研究。

Stem cell number control is the central question that understanding tissue homeostasis, cancer and aging during individual development. Drosophila pupal intestinal stem cell asymmetrically divides first, then symmetrically divides again, generating one pair of stem cells and one pair of enteroendocrine (ee) cells, forming 1200 stem cells before eclosion. We found that the cell polarity protein Mira segregates ee transcription factor Pros into the basal daughter cell during asymmetric divisions. However, Mira expression is absent during symmetric division and as a consequence Pros symmetrically distributes into two daughter cells. We wondered that Mira is the key factor that determining stem cell number. When we ectopic expressed Mira in ee cells, stem cell number was doubled while ee cell number is not affected. Surprisingly, stem cell number is also increased by 2 folds when we knockout or knockdown mira in the stem cell lineage. Our data support a hypothesis that Mira precisely determines intestinal stem cell number by controlling the threshold of Pros. In order to establish intestinal stem cell asymmetric division paradigm that determining stem cell number, we are applying for this funding opportunity to support our next cellular, molecular, genetic, and sequencing experiments to further examine our hypothesis.