The developing wing crossvein of Drosophila melanogaster: a fascinating model for signaling and morphogenesis.

The wing has been used as a model for studying tissue growth, morphogenesis and pattern formation. The wing veins of are composed of two distinct structures, longitudinal veins and crossveins. Although positional information of longitudinal veins is largely defined in the wing imaginal disc during the larval stage, crossvein primordial cells appear to be naive until the early pupal stage. Here, we first review how wing crossveins have been investigated in the past. Then, the developmental mechanisms underlying crossvein formation are summarized. This review focuses on how a conserved trafficking mechanism of BMP ligands is utilized for crossvein formation, and how various co-factors play roles in sustaining BMP signalling. Recent findings further reveal that crossvein development serves as an excellent model to address how BMP signal and dynamic cellular processes are coupled. This comprehensive review illustrates the uniqueness, scientific value and future perspectives of wing crossvein development as a model.