Fluorescence dynamics of lysosomal-related organelle flashing in the intestinal cells of Caenorhabditis elegans

The biological roles of the autofluorescent lysosome-related organelles (“gut granules”) in the intestinal cells of many nematodes, including Caenorhabditis elegans, have been shown to play an important role in metabolic and signaling processes, but they have not been fully characterized. We report here a previously undescribed phenomenon in which the autofluorescence of these granules increased and then decreased in a rapid and dynamic manner that may be associated with nutrient availability. We observed that two distinct types of fluorophores are likely present in the gut granules. One displays a “flashing” phenomenon, in which fluorescence decrease is preceded by a sharp increase in fluorescence intensity that expands into the surrounding area, while the other simply decreases in intensity. Gut granule flashing was observed in the different life stages of C. elegans and was also observed in Steinernema hermaphroditum, an evolutionarily distant nematode. We hypothesize that the “flashing” fluorophore is pH-sensitive, and the fluorescence intensity change results from the fluorophore being released from the lysosome-related organelles into the relatively higher pH environment of the cytosol. The visually spectacular dynamic fluorescence phenomenon we describe might provide a handle on the biochemistry and genetics of these lysosome-related organelles.