Dynamics of Cell Fate Specification in Drosophila Trachea

During formation of tracheal dorsal branches in Drosophila, around six initially identical cells adopt three distinct cell fates through a combination of external cues and cell-cell coordination. With a modest number of cells involved, this system is tractable for experimental and theoretical study, yet it still exhibits rich developmental phenomena. As an example, perturbing RAS signaling results in partially penetrant phenotypes and unmasks cryptic variation — branches that were seemingly identical in the wild-type appear distinct in mutants. To investigate this phenotypic variability, we construct probabilistic models for cell fate and perform Bayesian inference to test statistically whether outcomes differ across branches. Moving beyond static phenotypes, we perform live imaging in wild-type and mutant backgrounds allowing us to observe developmental dynamics in precise detail. From these movies, we segment individual branches and extract time-resolved shapes along with introducing morphometric descriptors that capture progressive branch elongation and terminal cell protrusions. Altogether, we show how tracheal development can serve as a compact model for quantitatively studying cell-fate transitions and variability in development.