No evidence for presence of maternal mitochondrial DNA in the sperm of Mytilus galloprovincialis males

Abstract

Species of the mussel family Mytilidae have a special mitochondrial DNA (mtDNA) transmission system, known as doubly uniparental inheritance (DUI), which consists of a maternally inherited (F) and a paternally inherited (M) mitochondrial genome. Females are normally homoplasmic for the F genome and males are heteroplasmic mosaics, with their somatic tissues dominated by the maternal and their gonads dominated by the paternal genome. Several studies have indicated that the maternal genome may often be present in the male germ line. Here we report the results from the examination of mtDNA in pure sperm from more than 30 males of Mytilus galloprovincialis . In all cases, except one, we detected only the M genome. In the sperm of one male, we detected a paternal genome with an F-like primary sequence that was different from the sequence of the maternal genome in the animal's somatic tissues. We conclude that the male germ line is protected against invasion by the maternal genome. This is important because fidelity of gamete-specific transmission of the two mitochondrial genomes is a basic requirement for the stability of DUI.

The Control Region of Maternally and Paternally Inherited Mitochondrial Genomes of Three Species of the Sea Mussel Genus Mytilus

“…The long type, on the other hand, was almost identical to that reported by Breton et al (2006). Assignment of the two CR types of M. trossulus to maternal and paternal genomes: The mere fact that a mitochondrial sequence is extracted from a female or a male individual, or even from a female or a male gonad, cannot be used as evidence that it is a maternally or paternally transmitted genome (Venetis et al 2006). The reason is that preparations from male gonads are, more often than not, contaminated by DNA from somatic cells that contain maternal mtDNA, and female tissues may contain small amounts of ''leaked'' paternal mtDNA (Garrido-Ramos et al 1998).…”

“…The particular C genome that was sequenced was isolated from sperm that were forced to swim through a Percoll solution for the removal of any debris from somatic cells. In a previous study it was shown that sperm purified in this way contain only paternal mtDNA (Venetis et al 2006). This produced firm evidence that the C genome is paternally inherited.…”

“…As a result, females are homoplasmic, even though small amounts of ''leaked'' paternal mtDNA can be detected in most of them (Stewart et al 1995;Garrido-Ramos et al 1998;Dalziel and Stewart 2002;Obata et al 2006), and males are heteroplasmic, with their somatic tissues dominated by the maternal mtDNA and the gonad dominated by the paternal. There is good evidence that pure sperm contain only the paternal mtDNA (Venetis et al 2006).…”

“…Pure spermatozoa were obtained from 10 males by forcing sperm to swim through a solution of Percoll as described in Venetis et al (2006). Eggs from five females were washed thoroughly with sterile sea water.…”

One tunic but more than one barcode: evolutionary insights from dynamic mitochondrial DNA inSalpa thompsoni(Tunicata: Salpida)

“…Heteroplasmy can arise when multiple mitochondrial haplotypes are inherited (Kmeic et al, 2006). A classic example of this is doubly uniparental inheritance in mussels, which was shown to generate intra individual cox1 variability in Mytilus L. species by Venetis et al (2006). Heteroplasmy can also arise de novo (typically as somatic variation) through recombination and small-scale mutations derived from replication and repair errors, as well as from the activity of reactive metabolites, in both large genomic and smaller fragments of mitochondrial DNA known as minicircles and sublimons (Kajander et al, 2000;Kmeic et al, 2006;Mao et al, 2014).…”