The Drosophila salivary glands (SGs) were well known for the puffing patterns of their polytene chromosomes and so became a tissue of choice to study sequential gene activation by the steroid hormone ecdysone. One well-documented function of these glands is to produce a secretory glue, which is released during pupariation to fix the freshly formed puparia to the substrate. Over the past two decades SGs have been used to address specific aspects of developmentally-regulated programmed cell death (PCD) as it was thought that they are doomed for histolysis and after pupariation are just awaiting their fate. More recently, however, we have shown that for the first 3-4 h after pupariation SGs undergo tremendous endocytosis and vacuolation followed by vacuole neutralization and membrane consolidation. Furthermore, from 8 to 10 h after puparium formation (APF) SGs display massive apocrine secretion of a diverse set of cellular proteins. Here, we show that during the period from 11 to 12 h APF, the prepupal glands are very active in calcium oxalate (CaOx) extrusion that resembles renal or nephridial excretory activity. We provide genetic evidence that Prestin, a Drosophila homologue of the mammalian electrogenic anion exchange carrier SLC26A5, is responsible for the instantaneous production of CaOx by the late prepupal SGs. Its positive regulation by the protein kinases encoded by fray and wnk lead to increased production of CaOx. The formation of CaOx appears to be dependent on the cooperation between Prestin and the vATPase complex as treatment with bafilomycin A1 or concanamycin A abolishes the production of detectable CaOx. These data demonstrate that prepupal SGs remain fully viable, physiologically active and engaged in various cellular activities at least until early pupal period, that is, until moments prior to the execution of PCD.

Department of Biology University of Nebraska at Omaha 6001 Dodge Street Omaha Nebraska 68182 0040 USA

Faculty of Agrobiology Food and Natural Resources Czech Agricultural University Kamýcká 129 16521 Prague 6 Czech Republic

Institute of Cellular Biology and Pathology 1st Faculty of Medicine Charles University Prague Albertov 4 12800 Prague Czech Republic

Laboratory of Developmental Genetics Institute of Experimental Endocrinology Biomedical Centre Slovak Academy of Sciences Dúbravská cesta 9 84505 Bratislava Slovakia

Laboratory of Developmental Genetics Institute of Experimental Endocrinology Biomedical Centre Slovak Academy of Sciences Dúbravská cesta 9 84505 Bratislava Slovakia Department of Genetics Comenius University Mlynská dolina B 1 84215 Bratislava Slovakia

Laboratory of Developmental Genetics Institute of Experimental Endocrinology Biomedical Centre Slovak Academy of Sciences Dúbravská cesta 9 84505 Bratislava Slovakia Department of Medical Biochemistry Jessenius Faculty of Medicine Comenius University Malá Hora 4 03601 Martin Slovakia

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