The aim of this study was to investigate whether bovine spermatozoa possess
so-called sperm factor in the cytosolic fraction (CF) which activates bovine
oocytes, and whether bovine oocytes matured in vitro are activated
by microinjection of CF extracted from spermatozoa of other species. In the
first experiment, bovine and human spermatozoa were microinjected into
ooplasm of bovine oocytes matured in vitro. Secondly, CF from
bovine and human spermatozoa were injected into bovine oocytes. In the
third, CF from human spermatozoa was injected into human unfertilised
oocytes obtained 18-20 h after clinical intracytoplasmic sperm injection
(ICSI). We found that microinjection of bovine spermatozoa into bovine
oocytes induced oocyte activation, as shown by resumption of meiosis and
formation of a female pronucleus, at a significantly higher rate than the
bovine sham injection (63.0% vs 43.0%; p < 0.05). On the other
hand, there was no significant difference in activation rate between the
human sperm injection (35.9%) and the human sham injection
(22.9%). Furthermore, microinjection of bovine sperm CF into bovine oocytes
induced oocyte activation at a significantly higher rate than the human CF
injection or sham injection (75.9% vs 14.8%, 20.4%; p < 0.01). Formation
of a single female pronucleus and second polar body extrusion was observed
in 95.1% of activated oocytes after bovine sperm CF injection. When human
sperm CF was injected into human unfertilised oocytes, the activation rate
was significantly higher than following sham injection (76.9% vs 44.0%;
p < 0.05). These results indicate the presence of sperm factor
in bovine sperm CF which activate bovine oocytes, and suggest the possibility
that sperm factor has species-specificity at least between bovine and human.
Accumulation of Carnitine by Bovine Spermatozoa during Maturation in the Epididymis
