The Arf family G protein Arl1 is required for secretory granule biogenesis in Drosophila

Abstract

The small G protein Arf like 1 (Arl1) is found at the Golgi apparatus, and in the GTP-bound form it recruits to the Golgi several effectors including GRIP-domain containing coiled-coil proteins, and the Arf1 exchange factors Big1/2. To investigate the role of Arl1, we have characterised a loss of function mutant of the Drosophila Arl1 orthologue. The gene is essential, and examination of clones of cells lacking Arl1 shows that it is required for recruitment of three of the four GRIP domain golgins to the Golgi, with dGCC185 being less dependent on Arl1. At a functional level, Arl1 is essential for formation of secretory granules in the larval salivary gland. When Arl1 is missing, the Golgi are still present but there is a dispersal of AP-1, a clathrin adaptor that requires Arf1 for its membrane recruitment and which is known to be required for secretory granule biogenesis. Arl1 does not appear to be required for AP-1 recruitment in all tissues, suggesting that it is critically required to enhance Arf1 activation at the trans-Golgi in particular tissues.