Sphingolipid transporter. Expressed in yolk cells. Expressed both maternally and zygotically throughout embryogenesis, and also in adults. Presence in early embryos of an opaque substance in the posterior yolk cell extension at approximately 1 day after fertilization. This material progressively accumulates and by 48 hours after fertilization fills the entire yolk. By day 3 of embryogenesis, embryos are severely reduced in size compared with their wild-type siblings and they die a few hours later. Belongs to the major facilitator superfamily. Spinster (TC 2.A.1.49) family.