Endocytotic vacuolation and vacuole acidification act in concert during early-to-mid prepupal development of Drosophila salivary glands.

Endocytotic vacuolation and vacuole acidification act in concert during early-to-mid prepupal development of Drosophila salivary glands. Robert Farkas¹, Denisa Benova-Liszekova¹, Zuzana Datkova^1,2, Daniel Vlcek², Milan Beno^1,2, Ludmila Pecenova^1,2, Otakar Raska³, Pavel Juda³, Lubos Kovacik³, Ivan Raska³, Bernard Mechler^3,4. 1) Inst Experimental Endocrinology, Slovak Academy Sciences, Vlarska 3, 83306 Bratislava, Slovakia; 2) Department of Genetics, Faculty of Science, Comenius University, Bratislava, Slovakia; 3) Institute of Cellular Biology and Pathology, 1st Faculty of Medicine, Charles University, Prague, Czech Republic; 4) Department of Developmental Genetics, Deutsches Krebsforschungszentrum-ZMBH Allianz, Heidelberg, Germany.

Larval salivary gland (SG) disintegration occurs 14-16 hr after puparium formation and is induced by the ecdysone hormone produced at the end of the larval development. Early during prepupal development, the cytoplasm of the SG cells undergoes an intense vacuolation resulting from endosomal recycling accompanied by strong acidification of the vacuoles. Here we show that vacuolation can be precociously initiated in late wandering third instar larvae by expressing transgenes for shi, syntaxins, Rab5, and Rab11. However, by comparison to prepupal vacuoles the larval vacuoles were poorly acidified. By manipulating vhaSFD, vha13, vha100.1, vha55, vha 26, and vhaAC39-1 we were able to show that the acidification of small basally-derived endosomes was distinct from the acidification of large apically-derived endosomes. Moreover we obtained evidence that the optimal and evenly distribution of acidified endosomes resulted from regulated fusion between large apical and small basal endosomes, which carry metabolic iron. These data indicate that before implementation of program cell death the SG cells are highly active in endosomal trafficking to provide resources for anabolic reactions. (Supported by the GACR grants P302/11/1640 and P302/12/G157, grants from Charles University UNCE 204022 and Prvouk/1LF/1, VEGA 2/0170/10, EEA & NFM Norwegian Fund # SK-0086/3655/2009/ORINFM).