Localization of prosaposin in rat cochlea.
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.
Terashita
Takehiro
T
Department of Basic Medical Research and Education, Ehime University School of Medicine, Shitsukawa, Toon, Ehime, Japan. terasita@m.ehime-u.ac.jp
Saito
Shouichiro
S
Miyawaki
Kyojy
K
Hyodo
Masamitsu
M
Kobayashi
Naoto
N
Shimokawa
Tetsuya
T
Saito
Kyoko
K
Matsuda
Seiji
S
Gyo
Kiyofumi
K
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
D009414:Nerve Growth Factors; C483347:Psap protein, rat; D012333:RNA, Messenger; D049231:Saposins; D002402:Cathepsin D