Characterizing Various Cup Proteins Involved in Lysosome Formation and Transport

Lysosomes are the main degradative organelles in eukaryotic cells and are essential for many cellular processes, including endocytosis, apoptosis, and autophagy. However, little is known about how they form. Endocytosed material is trafficked from early endosomes to late endosomes; materials destined for degradation are concentrated in structures that bud and separate from late endosomes, forming lysosomes. Acid hydrolases and other enzymes responsible for degradation are trafficked to these lysosomes to effect degradation. There are only two genes known to be essential for lysosome formation, rab-2 and cup-5 in Caenorhabditis elegans. Due to the complexity of lysosome formation, which includes budding, extension, and fission, we hypothesize that there are other genes involved in lysosome formation. A mutagenesis screen was conducted to identify different genes involved in lysosome formation. We used transgenic wild type C. elegans that secrete green fluorescent protein (GFP) from the body wall muscles into the body cavity of the worm; this GFP is endocytosed and degraded in lysosomes of scavenger cells called coelomocytes. We mutagenized these worms and identified mutants that had bright green coelomocytes indicative of defects in lysosome formation and/or function. We report our analysis of these new cup mutants and their possible functions in lysosomes