Probable sphingolipid transporter that plays a central role in endosomes and/or lysosomes storage. Involved in TGF-beta-mediated synaptic growth regulation both pre- and postsynaptically via its function in endosomal storage regulation. Also required during oogenesis by regulating yolk spheres storage. Enriched in brain (at protein level). Expressed in both motoneurons and muscle throughout the period of synaptic growth and development at the neuromuscular junction. Expressed throughout the CNS, including motoneurons. Weak expression is observed in embryonic muscle as well as other tissues. Expressed throughout the larval CNS with pronounced expression in motoneurons. Also strongly expressed in all body wall muscle as well as other tissues, including a subset of epithelial cells and the salivary glands. In most cases, death at the late pupal stage, probably due to lipid accumulation in endosomes/lysosomes. Some flies survive until adulthood and display a strong rejection behavior of female flies in response to male courtship accompanied by decreases in the viability, adult life span, and oviposition rate of the flies. Some oocytes and adult neural cells undergo degeneration, which is preceded by reductions in programmed cell death of nurse cells in ovaries and of neurons in the pupal nervous system, respectively. The central nervous system (CNS) of flies accumulates lipopigments. Flies also display a strong synaptic overgrowth: synapses reveal a strong increase in bouton number and a deficit in presynaptic release caused by enhanced/misregulated TGF-beta signaling. A widespread accumulation of enlarged lysosomal and late endosomal inclusions is also present in yolk spheres during oogenesis. Belongs to the major facilitator superfamily. Spinster (TC 2.A.1.49) family. Truncated N-terminus.