The timing of Drosophila salivary gland apoptosis displays an l(2)gl-dose response

During Drosophila metamorphosis, larval tissues, such as the salivary gland s, are histolysed whereas imaginal tissues differentiate into adult structu res forming at eclosion a fly-shaped adult. Inactivation of the lethal(2)gi ant larvae (I(2)gl) gene encoding the cytoskeletal associated p127 protein, causes malignant transformation of brain neuroblasts and imaginal disc cel ls with developmental arrest at the larval-pupal transition phase. At this stage, p127 is expressed in wildtype salivary glands which become fully his tolysed 12-13 h after pupariation. By contrast to wild-type, administration of 20-hydroxyecdsone to I(2)gl-deficient salivary glands is unable to indu ce histolysis, although it releases stored glue granules and gives rise to a nearly normal pupariation chromosome puffing, indicating that p127 is req uired for salivary gland apoptosis, To unravel the I(2)gl function in this tissue we used transgenic lines expressing reduced (similar to 0.1) or incr eased levels of p127 (3.0). Here we show that the timing of salivary gland histolysis displays an I(2)gl-dose response. Reduced p127 expression delays histolysis whereas overexpression accelerates this process without affecti ng the duration of third larval instar, prepupal and pupal development. Sim ilar I(2)gl-dependence is noticed in the timing of expression of the cell d eath genes reaper, head involution defective and grim, supporting the idea that p127 plays a critical role in the implementation of ecdysone-triggered apoptosis, These experiments show also that the timing of salivary gland a poptosis can be manipulated without affecting normal development and provid e ways to investigate the nature of the components specifically involved in the apoptotic pathway of the salivary glands.