title: Localization of prosaposin in rat cochlea.
abstract: Prosaposin, the precursor of the sphingolipid hydrolase activator proteins called saposins A, B, C, and D, is abundant in the nervous system and muscles. Besides its role as the precursor of saposins, prosaposin is reported to function as a neurotrophic factor, initiating neural differentiation and preventing neuronal cell death in vivo and in vitro. In this study, we examined the localization and synthesis of prosaposin in the rat cochlea. Intense prosaposin immunoreactivity was observed in the organ of Corti, stria vascularis, and spiral ganglion. In an immuno-electron microscopic study, prosaposin immunoreactivity was found mainly in lysosomal granules of the cells in these regions. In the lysosome, prosaposin does not always colocalize with cathepsin D, but was localized mainly in the dark area of the lysosome. Prosaposin mRNA was observed in these same regions. Our results suggest that prosaposin plays a role in homeostasis in the peripheral auditory system.
authors.affiliation: Department of Basic Medical Research and Education, Ehime University School of Medicine, Shitsukawa, Toon, Ehime, Japan. terasita@m.ehime-u.ac.jp
authors.forename: Takehiro
authors.initials: T
authors.lastname: Terashita
authors.forename: Shouichiro
authors.initials: S
authors.lastname: Saito
authors.forename: Kyojy
authors.initials: K
authors.lastname: Miyawaki
authors.forename: Masamitsu
authors.initials: M
authors.lastname: Hyodo
authors.forename: Naoto
authors.initials: N
authors.lastname: Kobayashi
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Shimokawa
authors.forename: Kyoko
authors.initials: K
authors.lastname: Saito
authors.forename: Seiji
authors.initials: S
authors.lastname: Matsuda
authors.forename: Kiyofumi
authors.initials: K
authors.lastname: Gyo
mesh_terms: D000818:Animals; D002402:Cathepsin D / Q000378:metabolism; D002470:Cell Survival / Q000502:physiology; D003051:Cochlea / Q000378:metabolism* / Q000648:ultrastructure; D005260:Female; D006198:Hair Cells, Auditory / Q000378:metabolism / Q000648:ultrastructure; D006706:Homeostasis / Q000502:physiology; D008247:Lysosomes / Q000378:metabolism / Q000648:ultrastructure; D008297:Male; D016253:Microscopy, Immunoelectron; D009414:Nerve Growth Factors / Q000378:metabolism*; D009475:Neurons, Afferent / Q000378:metabolism / Q000648:ultrastructure; D009925:Organ of Corti / Q000378:metabolism / Q000648:ultrastructure; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D049231:Saposins / Q000096:biosynthesis* / Q000235:genetics; D013136:Spiral Ganglion / Q000378:metabolism / Q000648:ultrastructure; D013316:Stria Vascularis / Q000378:metabolism / Q000648:ultrastructure
chemical_list: D009414:Nerve Growth Factors; C483347:Psap protein, rat; D012333:RNA, Messenger; D049231:Saposins; D002402:Cathepsin D