Abstract
Clathrin interactor 1 [CLINT1] (also called enthoprotin/EpsinR) is an Epsin N-terminal homology (ENTH) domain-containing adaptor protein that functions in anterograde and retrograde clathrin-mediated trafficking between the trans-Golgi network and the endosome. Removal of both Saccharomyces cerevisiae homologs, Ent3p and Ent5p, result in yeast that are viable, but that display a cold-sensitive growth phenotype and mistrafficking of various vacuolar proteins. Similarly, either knock-down or overexpression of vertebrate CLINT1 in cell culture causes mistrafficking of proteins. Here, we have characterized Drosophila CLINT1, liquid-facets Related (lqfR). LqfR is ubiquitously expressed throughout development and is localized to the Golgi and endosome. Strong hypomorphic mutants generated by imprecise P-element excision exhibit extra macrochaetae, rough eyes and are female sterile. Although essentially no eggs are laid, the ovaries do contain late-stage egg chambers that exhibit abnormal morphology. Germline clones reveal that LqfR expression in the somatic follicle cells is sufficient to rescue the oogenesis defects. Clones of mutant lqfR follicle cells have a decreased cell size consistent with a downregulation of Akt1. We find that while total Akt1 levels are increased there is also a significant decrease in activated phosphorylated Akt1. Taken together, these results show that LqfR function is required to regulate follicle cell size and signaling during Drosophila oogenesis.
Highlights
Vesicular trafficking is required in eukaryotes for the movement of membranes, proteins, and other bioactive molecules between cellular compartments
Epsins bind to a specific subset of membrane and to proteins marked for endocytosis by ubiquitin, and recruit clathrin and the tetrameric clathrin adaptor AP-2
Drosophila liquid-facets Related (lqfR) encodes two distinct transcripts To study the function of CLINT in a multicellular organism we first identified the Drosophila melanogaster homolog of CLINT1
Summary
Vesicular trafficking is required in eukaryotes for the movement of membranes, proteins, and other bioactive molecules between cellular compartments. Clathrin-mediated vesicle formation is found principally at three locations in the cell: at the plasma membrane during endocytosis; at the trans-Golgi network (TGN) during the formation of some vesicles that traffic to the endosome; and at the endosome for trafficking back to the TGN [1]. Adaptor proteins help mediate the recruitment of clathrin to appropriate membrane and sites of cargo enrichment. One such set of adaptors is the epsin family of proteins, which are found at the plasma membrane. They contain a phosphatidylinositol 4,5bisphosphate-binding ENTH domain [2], and motifs for interaction with clathrin [3], other cargo adaptors, and ubiquitylated proteins. The insertion of a helix of the ENTH domain between the polar heads of the lipid membrane is thought to help induce curvature of the developing clathrin-coated pit [4]
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