Most tubes have seams (intercellular or autocellular junctions that seal 
membranes together into a tube), but "seamless" tubes also exist. In Drosophila, 
stellate-shaped tracheal terminal cells make seamless tubes, with single 
branches running through each of dozens of cellular extensions. We find that 
mutations in braided impair terminal cell branching and cause formation of 
seamless tube cysts. We show that braided encodes Syntaxin7 and that cysts also 
form in cells deficient for other genes required either for membrane scission 
(shibire) or for early endosome formation (Rab5, Vps45, and Rabenosyn-5). These 
data define a requirement for early endocytosis in shaping seamless tube lumens. 
Importantly, apical proteins Crumbs and phospho-Moesin accumulate to aberrantly 
high levels in braided terminal cells. Overexpression of either Crumbs or 
phosphomimetic Moesin induced lumenal cysts and decreased terminal branching. 
Conversely, the braided seamless tube cyst phenotype was suppressed by mutations 
in crumbs or Moesin. Indeed, mutations in Moesin dominantly suppressed seamless 
tube cyst formation and restored terminal branching. We propose that early 
endocytosis maintains normal steady-state levels of Crumbs, which recruits 
apical phosphorylated (active) Moe, which in turn regulates seamless tube shape 
through modulation of cortical actin filaments.