Secreted d‐aspartate oxidase functions in C. elegans reproduction and development.

d‐Aspartate oxidase (DDO) is a degradative enzyme that acts stereospecifically on free acidic D‐amino acids such as d‐aspartate and d‐glutamate. d‐Aspartate plays an important role in regulating neurotransmission, developmental processes, hormone secretion, and reproductive functions in mammals. In contrast, the physiological role of d‐glutamate in mammals remains unclear. In Caenorhabditis elegans, the enzyme responsible for in vivo metabolism of d‐glutamate is DDO‐3, one of the three DDO isoforms, which is also required for normal self‐fertility, hatching, and lifespan. In general, eukaryotic DDOs localize to subcellular peroxisomes in a peroxisomal targeting signal type 1 (PTS1)‐dependent manner. However, DDO‐3 does not contain a PTS1, but instead has a putative N‐terminal signal peptide (SP). In this study, we found that DDO‐3 is a secreted DDO, the first such enzyme to be described in eukaryotes. In hermaphrodites, DDO‐3 was secreted from the proximal gonadal sheath cells in a SP‐dependent manner and transferred to the oocyte surface. In males, DDO‐3 was secreted from the seminal vesicle into the seminal fluid in a SP‐dependent manner during mating with hermaphrodites. In both sexes, DDO‐3 was secreted from the cells where it was produced into the body fluid and taken up by scavenger coelomocytes. Full‐length DDO‐3 transgene rescued all phenotypes elicited by the deletion of ddo‐3, whereas a DDO‐3 transgene lacking the putative SP did not. Together, these results indicate that secretion of DDO‐3 is essential for its physiological functions. Eukaryotic d‐aspartate oxidase (DDO) is an enzyme that stereospecifically degrades free acidic d‐amino acids and is usually localized to the peroxisome. Saitoh et al. now describe the first secreted eukaryotic DDO in C. elegans, DDO‐3, and demonstrate that secretion of DDO‐3 is essential for normal fertility, hatching, lifespan, and nose touch response. [ABSTRACT FROM AUTHOR]