The de novo formation and maintenance of C. elegans lysosome-related organelles.

Lysosome-related organelles (LROs) are cell-type-specific organelles derived from the endosomal system. Their lack of ubiquity requires that they be created during cell differentiation. To investigate how LROs are first formed, we characterized the biogenesis of Caenorhabditis elegans gut granules and found that these intestinally restricted LROs are generated de novo during a short period of early embryogenesis. Intriguingly, we found that gut granule number and size remain unchanged throughout the rest of embryonic development. The transition from formation to maintenance coincides with the loss of the GLO-1/Rab32 guanine nucleotide exchange factor (GEF) subunit CCZ-1 from gut granules. Our investigations manipulating the presence and activity of GLO-1/Rab32 reveal that LRO biogenesis remains active during embryogenesis when the steady-state number of gut granules does not change. These studies define a system where the de novo formation of LROs can be investigated and provide insights into the mechanisms maintaining LROs once they have been generated.