Spergen-1 might be an adhesive molecule associated with mitochondria in the middle piece of spermatozoa.
Spergen-1, a recently identified molecule specifically expressed in haploid spermatids in testis, is a small protein of 154 amino acids with a mitochondria-targeting signal at the N terminus. To examine the localization of spergen-1 protein in germ cells, we performed immunocytochemistry with the anti-spergen-1 antibody on frozen sections of rat testis and purified spermatozoa. Immunolabeling for spergen-1 was detected in mitochondria of elongating spermatids and of the middle pieces of matured spermatozoa. Immunoelectron microscopy revealed that spergen-1 was localized to the surface of mitochondria in the middle piece of spermatozoa. To investigate the properties of spergen-1, COS-7 cells were transfected with vectors encoding various spergen-1 mutants. The transfection experiments showed that spergen-1 expressed in the cells tended to agglutinate mitochondria and assemble them into aggregations and that the C-terminal region of spergen-1 as well as the N-terminal mitochondrial targeting signal was requisite for induction of mitochondrial aggregation. These results suggest that spergen-1, a mitochondria-associated molecule in spermatozoa, has a property to induce mitochondrial aggregation at least in cultured cells. We hypothesize that spergen-1 might function as an adhesive molecule to assemble mitochondria into the mitochondrial sheath around the outer dense fibers during spermiogenesis.
Doiguchi
Masamichi
M
Laboratory of Zoology, Graduate School of Agriculture, Kyushu University, Higashiku Hakozaki 6-10-1, Fukuoka 812-8581 Japan.
Mori
Takayuki
T
Toshimori
Kiyotaka
K
Shibata
Yosaburo
Y
Iida
Hiroshi
H
D000818:Animals; D019556:COS Cells; D007150:Immunohistochemistry; D008297:Male; D016253:Microscopy, Immunoelectron; D008928:Mitochondria / Q000378:metabolism*; D011506:Proteins / Q000378:metabolism / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D013094:Spermatozoa / Q000648:ultrastructure*; D013737:Testis / Q000378:metabolism / Q000648:ultrastructure
D011506:Proteins; C464881:Spata19 protein, rat