Abstract
BackgroundIn animals mtDNA inheritance is maternal except in certain molluscan bivalve species which have a paternally inherited mitochondrial genome (genome M) along with the standard maternal one (genome F). Normally, the paternal genome occurs in the male gonad, but it can be often found, as a minority, in somatic tissues of males and females. This may happen in two ways. One is through "sperm mtDNA leakage" into somatic tissues, a deviation from the normal situation in which the sperm mtDNA vanishes in females or ends up exclusively in the germ line of males. The other is through "egg heteroplasmy", when the egg contains, in small quantities, the paternal genome in addition to maternal genome.FindingsTo test the two hypotheses, we compared the sequences of one of the most variable domains of the M molecule in a somatic tissue (foot) and in the sperm of ten male and in the foot of ten female individuals of M. galloprovincialis. Presence of the M genome was rarer in the foot of females than males. The M genome in the sperm and in the foot of males was identical.ConclusionsGiven that the surveyed region differs from individual to individual, the identity of the M genome in the foot and the sperm of males supports strongly the hypothesis that, at least for the tissue examined, the presence of the M genome is due to sperm mtDNA leakage.
Highlights
In animals mitochondrial DNA (mtDNA) inheritance is maternal except in certain molluscan bivalve species which have a paternally inherited mitochondrial genome along with the standard maternal one
Given that the surveyed region differs from individual to individual, the identity of the M genome in the foot and the sperm of males supports strongly the hypothesis that, at least for the tissue examined, the presence of the M genome is due to sperm mtDNA leakage
Contrary to the general rule of maternal inheritance of mitochondrial DNA in metazoans [1,2,3], in some bivalve mollusks we observe the phenomenon of Doubly Uniparental Inheritance (DUI), according to which a maternally inherited mitochondrial genome is present in the eggs and the somatic tissues of female and male individuals, whereas a different paternally inherited mitochondrial genome appears in the male germ line [4,5,6,7]
Summary
Given that the surveyed region differs from individual to individual, the identity of the M genome in the foot and the sperm of males supports strongly the hypothesis that, at least for the tissue examined, the presence of the M genome is due to sperm mtDNA leakage
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