Eclosion muscles secrete ecdysteroids to initiate asymmetric intestinal stem cell division in Drosophila.

During organ development, tissue stem cells first expand via symmetric divisions and then switch to asymmetric divisions to minimize the time to obtain a mature tissue. In the Drosophila midgut, intestinal stem cells switch their divisions from symmetric to asymmetric at midpupal development to produce enteroendocrine cells. However, the signals that initiate this switch are unknown. Here, we identify the signal as ecdysteroids. In the presence of ecdysone, EcR and Usp promote the expression of E93 to suppress Br expression, resulting in asymmetric divisions. Surprisingly, the primary source of pupal ecdysone is not from the prothoracic gland but from dorsal internal oblique muscles (DIOMs), a group of transient skeletal muscles that are required for eclosion. Genetic analysis shows that DIOMs secrete ecdysteroids during mTOR-mediated muscle remodeling. Our findings identify sequential endocrine and mechanical roles for skeletal muscle, which ensure the timely asymmetric divisions of intestinal stem cells.

Intravital imaging strategy FlyVAB reveals the dependence of Drosophila enteroblast differentiation on the local physiology.

Aging or injury in Drosophila intestine promotes intestinal stem cell (ISC) proliferation and enteroblast (EB) differentiation. However, the manner the local physiology couples with dynamic EB differentiation assessed by traditional lineage tracing method is still vague. Therefore, we developed a 3D-printed platform "FlyVAB" for intravital imaging strategy that enables the visualization of the Drosophila posterior midgut at a single cell level across the ventral abdomen cuticle. Using ISCs in young and healthy midgut and enteroendocrine cells in age-associated hyperplastic midgut as reference coordinates, we traced ISC-EB-enterocyte lineages with Notch signaling reporter for multiple days. Our results reveal a "differentiation-poised" EB status correlated with slow ISC divisions and a "differentiation-activated" EB status correlated with ISC hyperplasia and rapid EB to enterocyte differentiation. Our FlyVAB imaging strategy opens the door to long-time intravital imaging of intestinal epithelium.