Selective and continuous elimination of mitochondria microinjected into mouse eggs from spermatids, but not from liver cells, occurs throughout embryogenesis
H. Shitara et al., Selective and continuous elimination of mitochondria microinjected into mouse eggs from spermatids, but not from liver cells, occurs throughout embryogenesis, GENETICS, 156(3), 2000, pp. 1277-1284
Exclusion of paternal mitochondria in fertilized mammalian eggs is very str
ingent and ensures strictly maternal mtDNA inheritance. In this study, to e
xamine whether elimination was specific to sperm mitochondria, we microinje
cted spermatid or liver mitochondria into mouse embryos. Congenic B6-mt(spr
) strain mice, which are different from C57BL/6J (BG) strain mice (Mus musc
ulus domesticus) only in possessing M. spretus mtDNA, were used as mitochon
drial donors. B6-mt(spr) mice and a quantitative PCR method enabled selecti
ve estimation of the amount of M. spretus mtDNA introduced even in the pres
ence of host M m. domesticus mtDNA and monitoring subsequent changes of its
amount during embryogenesis. Results showed that M. spretus mtDNA in sperm
atid mitochondria was not eliminated by the blastocyst stage, probably due
to the introduction of a larger amount of spermatid mtDNA than of sperm mtD
NA into embryos on fertilization. However, spermatid-derived M. spretus mtD
NA was eliminated by the time of birth, whereas liver-derived nl. spretus m
tDNA was still present ill most newborn mice, even though its amount introd
uced was significantly less than that of spermatid mtDNA. These observation
s suggest that mitochondria from spermatids but not from liver have specifi
c factors that ensure their selective elimination and resultant elimination
of mtDNA in them, and that the occurrence of elimination is not limited to
early stage embryos, but continues throughout embryogenesis.