The P{XP}serpd03931 element is inserted in the serp 5'UTR, 228bp upstream of the first ATG.
Stage 16 serpd03931 mutant embryos display irregular and elongated tracheal cell shapes compared to wild-type.
In wild-type, tracheal tubes consist of tightly packed luminal chitin polymers. In hemizygous serpd03931 mutants these structures appear diffuse and radially expanded.