Human SP-10: acrosomal distribution, processing, and fate after the acrosome reaction.
SP-10 is a testis-specific acrosomal protein that has been detected in several species including humans. Extracts from whole human testis and epididymal, ejaculated, and capacitated sperm were analyzed by Western blot for SP-10 polypeptides. The testis extracts contained a full-length SP-10 protein at approximately 45 kDa as well as other immunoreactive SP-10 peptides at 32, 30, 28, and 26 kDa. Extracts from epididymal, ejaculated, and capacitated sperm contained several immunoreactive SP-10 peptides that co-migrated with the 32-26-kDa SP-10 peptides in the testis extracts. Epididymal, ejaculated, and capacitated sperm extracts did not contain the 45-kDa SP-10 peptide observed in testis extracts, but did contain immunoreactive SP-10 peptides from 25 to 18 kDa that were not detected in testis extracts. These results indicate that a full-length 45-kDa SP-10 precursor protein is present in the testis and that SP-10 peptides of 32, 30, 28, and 26 kDa result from proteolytic processing of the SP-10 precursor protein in the testis and/or alternative splicing. In addition, SP-10 peptides of 25-18 kDa were first detected in extracts of caput epididymal sperm and probably resulted from the proteolytic processing of the 45- and 32-26-kDa SP-10 peptides in the initial segment or caput epididymidis. Also, no additional SP-10 bands were detected in extracts of cauda epididymal, ejaculated, or capacitated sperm, suggesting that no further processing of the 32-18-kDa SP-10 peptides occurred during epididymal transit, ejaculation, and capacitation. Electron microscopic immunocytochemical observations of epididymal, ejaculated, and capacitated sperm revealed that colloidal gold labeling of SP-10 was most abundant within the principal segment and posterior bulb of the equatorial segment of the acrosome, while the colloidal gold labeling of SP-10 was sparse in the anterior equatorial segment of the acrosome. After a follicular fluid-induced acrosome reaction, SP-10 was detected on the inner acrosomal membrane in the equatorial segment and was associated with hybrid vesicles. This localization after the acrosome reaction is consistent with the hypothesis that SP-10 may be involved in sperm-zona binding or penetration.
Foster
J A
JA
Department of Cell Biology, University of Virginia, Charlottesville 22908.
Klotz
K L
KL
Flickinger
C J
CJ
Thomas
T S
TS
Wright
R M
RM
Castillo
J R
JR
Herr
J C
JC
D000177:Acrosome / Q000737:chemistry* / Q000378:metabolism / Q000502:physiology*; D000368:Aged; D000941:Antigens / Q000032:analysis* / Q000737:chemistry / Q000378:metabolism* / Q000502:physiology; D015153:Blotting, Western; D004822:Epididymis / Q000737:chemistry; D012739:Gonadal Steroid Hormones / Q000032:analysis* / Q000737:chemistry / Q000378:metabolism* / Q000502:physiology; D006801:Humans; D007150:Immunohistochemistry; D008297:Male; D008565:Membrane Proteins; D016253:Microscopy, Immunoelectron; D008875:Middle Aged; D017433:Protein Structure, Secondary; D013075:Sperm Capacitation; D013094:Spermatozoa / Q000737:chemistry / Q000648:ultrastructure; D013737:Testis / Q000737:chemistry
C512729:ACRV1 protein, human; D000941:Antigens; D012739:Gonadal Steroid Hormones; D008565:Membrane Proteins