Broad relays hormone signals to regulate stem cell differentiation in Drosophila midgut during metamorphosis.

Like the mammalian intestine, the Drosophila adult midgut is constantly replenished by multipotent intestinal stem cells (ISCs). Although it is well known that adult ISCs arise from adult midgut progenitors (AMPs), relatively little is known about the mechanisms that regulate AMP specification. Here, we demonstrate that Broad (Br)-mediated hormone signaling regulates AMP specification. Br is highly expressed in AMPs temporally during the larva-pupa transition stage, and br loss of function blocks AMP differentiation. Furthermore, Br is required for AMPs to develop into functional ISCs. Conversely, br overexpression drives AMPs toward premature differentiation. In addition, we found that Br and Notch (N) signaling function in parallel pathways to regulate AMP differentiation. Our results reveal a molecular mechanism whereby Br-mediated hormone signaling directly regulates stem cells to generate adult cells during metamorphosis.