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We recount the basic observations about doubly uniparental inheritance (DUI) of mtDNA in bivalvian mollusks with an emphasis on those that were obtained from work in Mytilus and appeared after the review by Zouros (Evol Biol 40:1–31, 2013). Using this information, we present a new model about DUI that is a revised version of previously suggested models. The model can be summarized as follows. A Mytilus female either provides its eggs with the “masculinizing” factor S and the “sperm mitochondria binding” factor Z, or it does not. This property of the female is determined by two nuclear genes, S and Z, that are always in the on/on or the off/off phase. In fertilized eggs without factors S and Z the embryo develops into a female and the sperm mitochondria are randomly dispersed among cells following development. In fertilized eggs with factors S and Z, the first factor causes the cell to become eventually sperm and the second causes the sperm mitochondria to aggregate and anchor to the nuclear membrane by binding to a specific motif of the sperm-derived mtDNA. Factors S and Z are continuously co-synthesized and co-localized in the cell line from the egg to the sperm. The sperm mitochondria of the aggregate escape the mechanism that eliminates the cell’s mitochondria before the formation of the sperm. The rescued mitochondria are subsequently packed into five mega-mitochondria in the sperm and are delivered in the egg. © 2019, Springer Nature Switzerland AG.

Species of Mytilus carry two mitochondrial genomes, one transmitted through the egg (F) and the other through the sperm (M). In a previous paper we showed that a specific part of the M genome binds with proteins originating from male gonadal extracts and proposed that this binding protects M carrying mitochondria from a destruction mechanism that occurs in the male gonad. Here we show that a similar binding with the homologous part of the F genome is less specific and unstable, and apparently offers no protection of F carrying mitochondria. © 2016 Elsevier Inc.

Sea mussels (genus Mytilus) have two mitochondrial genomes in obligatory co-existence, one that is transmitted through the egg and the other through the sperm. The phenomenon, known as Doubly Uniparental Inheritance (DUI) of mitochondrial DNA (mtDNA), is presently known to occur in more than 40 molluscan bivalve species. Females and the somatic tissues of males contain mainly the maternal (F) genome. In contrast, the sperm contains only the paternal (M) genome. Through electrophoretic mobility shift assay (EMSA) experiments we have identified a sequence element in the control region (CR) of the M genome that acts as a binding site for the formation of a complex with a protein factor that occurs in the male gonad. An adenine tract upstream to the element is also essential for the formation of the complex. The reaction is highly specific. It does not occur with protein extracts from the female gonad or from a male or female somatic tissue. Further experiments showed that the interaction takes place in mitochondria surrounding the nucleus of the cells of male gonads, suggesting a distinct role of perinuclear mitochondria. We propose that at a certain point during spermatogenesis mitochondria are subject to degradation and that perinuclear mitochondria with the M mtDNA-protein complex are protected from this degradation with the result that mature spermatozoa contain only the paternal mitochondrial genome. © 2015 Elsevier B.V.

Species of the genus Mytilus carry two mitochondrial genomes in obligatory coexistence; one transmitted though the eggs (the F type) and one through the sperm (the M type). We have studied the 3' and 5' ends of rRNA and tRNA transcripts using RT-PCR and RNA circularization techniques in both the F and M genomes of Mytilus galloprovincialis. We have found polyadenylated and non-adenylated transcripts for both ribosomal and transfer RNAs. In all these genes the 5' ends of the transcripts coincided with the first nucleotide of the annotated genes, but the 3' ends were heterogeneous. The l-rRNA 3' end is 47 or 48 nucleotides upstream from the one assigned by a previous annotation, which makes the adjacent first domain (variable domain one, VD1) of the main control region (CR) correspondingly longer. We have observed s-rRNA and l-rRNA transcripts with truncated 3' end and polyadenylated tRNA transcripts carrying the CCA trinucleotide. We have also detected polyadenylated RNA remnants carrying the sequences of the control region, which strongly suggests RNA degradation activity and thus presence of degradosomes in Mytilus mitochondria. © 2014 Elsevier B.V.

The control region of the mtDNA of Mytilus is known to contain sequences that determine whether the genome will be paternally or maternally transmitted. An open reading frame (ORF) in this region raised suspicion that it may code for a protein involved in this mechanism. An analysis of the mtDNA transcriptome failed to produce evidence for this hypothesis. © 2014 Elsevier B.V.

Transcription of the mitochondrial genomes of the Mediterranean mussel Mytilus galloprovincialis has been studied by RT-PCR and RNA circularization. This species has an egg-transmitted (F) and a sperm-transmitted (M) mitochondrial genome, in accordance with the doubly uniparental inheritance (DUI) pattern of mtDNA transmission. The primary transcript is cleaved into ten transcripts, eight of which are monocistronic, one is tricistronic and one is most likely, but not certainly, bicistronic. The start/end points of these transcripts have been determined. In the majority of cases cleavage is mediated according to the "tRNA punctuation" model. However, we have identified four cases of cleavage that do not coincide with the presence of a tRNA. In these cases transcription starts immediately or only a few bases from the end point of the preceding gene and cleavage is, most likely, mediated by a stem-loop structure formed at the start point of the gene. The identification of a tricistronic transcript is a novel finding for metazoan mtDNA. We propose that its evolution has been facilitated by the fact that all coding genes are transcribed from the same DNA strand and that co-transcription is sustained by selection emanating from the fact that proteins derived from all three co-transcribed genes participate in the formation of the same oxidative phosphorylation complex. © 2013 Elsevier B.V.

Homologous recombination is restricted to sequences of low divergence. This is attributed to the mismatch repairing system (MMR), which does not allow recombination between sequences that are highly divergent. This acts as a safeguard against recombination between nonhomologous sequences that could result in genome imbalance. Here, we report recombination between maternal and paternal mitochondrial genomes of the sea mussel, whose sequences differ by >20%. We propose that the strict maternal inheritance of the animal mitochondrial DNA and the ensuing homoplasmy has relieved the MMR system of the animal mitochondrion from the pressure to tolerate recombination only among sequences with a high degree of similarity. © The Author 2011. Published by Oxford University Press on behalf of the Society for Molecular Biology and Evolution. All rights reserved.

Endometriosis is the presence of ectopic endometrial tissue that can respond to ovarian hormonal stimulation. Although it is uncommon, extrapelvic endometriosis can form a discrete mass known as an abdominal wall endometrioma. Endometriomas are thought to be caused by transfer of endometrial cells into a surgical wound, most often after a cesarean delivery. Endometriomas are diagnosed via ultrasound, computed tomography, magnetic resonance imaging, and ultrasound-guided fine needle aspiration. Treatment options can be medical, but surgical excision is the treatment of choice. Perioperative nursing care includes patient teaching, taking steps to prevent surgical site infection and inadvertent hypothermia, ensuring availability of supplies (eg, the graft for abdominal wall repair if needed), and postoperative pain management. © 2010 AORN, Inc.

Species of the mussel genus Mytilus possess maternally and paternally transmitted mitochondrial genomes. In the interbreeding taxa Mytilus edulis and M. galloprovincialis, several genomes of both types have been fully sequenced. The genome consists of the coding part (which, in addition to protein and RNA genes, contains several small noncoding sequences) and the main control region (CR), which in turn consists of three distinct parts: the first variable (VD1), the conserved (CD), and the second variable (VD2) domain. The maternal and paternal genomes are very similar in gene content and organization, even though they differ by >20% in primary sequence. They differ even more at VD1 and VD2, yet they are remarkably similar at CD. The complete sequence of a genome from the closely related species M. trossulus was previously reported and found to consist of a maternal-like coding part and a paternal-like and a maternal-like CR. From this and from the fact that it was extracted from a male individual, it was inferred that this is a genome that switched from maternal to paternal transmission. Here we provide clear evidence that this genome is the maternal genome of M. trossulus. We have found that in this genome the lRNA Gln in the coding region is apparently defective and that an intact copy of this tRNA occurs in the CR, that one of the two conserved domains is missing essential motifs, and that one of the two first variable domains has a high rate of divergence. These features may explain the large size and mosaic structure of the CR of the maternal genome of M. trossulus. We have also obtained CR sequences of the maternal and paternal genomes of M. californianus, a more distantly related species. We compare the control regions from all three species, focusing on the divergence among genomes of different species origin and among genomes of different transmission routes. Copyright © 2009 by the Genetics Society of America.

Species of the marine mussel genus Mytilus are known to contain two mitochondrial genomes, one transmitted maternally (the F genome) and the other paternally (the M genome). The two genomes have diverged by more than 20% in DNA sequence. Here we present the complete sequence of a third genome, genome C, which we found in the sperm of a Mytilus galloprovincialis male. The coding part of the new genome resembles in sequence the F genome, from which it differs by about 2% on average, but differs from the M genome by as much as the F from the M. Its major control region (CR) is more than three times larger than that of the F or the M genome and consists of repeated sequence domains of the CR of the M genome flanked by domains of the CR of the F genome. We present a sequence of events that reconstruct most parsimoniously the derivation of the C genome from the F and M genomes. The sequence consists of a duplication of CR elements of the M genome and subsequent insertion of these tandemly repeated elements in the F genome by recombination. The fact that the C genome was found as the only mitochondrial genome in the sperm of the male from which it was extracted suggests that it is transmitted paternally. © 2007 Elsevier B.V. All rights reserved.

Several studies have shown that in vertebrate mtDNAs the nucleotide content at fourfold degenerate sites is well correlated with the site's time of exposure to the single-strand state, as predicted from the asymmetrical model of mtDNA replication. Here we examine whether the same explanation may hold for the regional variation in nucleotide content in the maternal and paternal mtDNAs of the mussel Mytilus galloprovincialis. The origin of replication of the heavy strand (OH) of these genomes has been previously established. A systematic search of the two genomes for sequences that are likely to act as the origin of replication of the light strand (OL) suggested that the most probable site lies within the ND3 gene. By adopting this OL position we calculated times of exposure for 0FD (nondegenerate), 2FD (twofold degenerate), and 4FD (fourfold degenerate) sites of the protein-coding part of the genome and for the rRNA, tRNA and noncoding parts. The presence of thymine and absence of guanine at 4 FD sites was highly correlated with the presumed time of exposure. Such an effect was not found for the 2FD sites, the rRNA, the tRNA, or the noncoding parts. There was a trend for a small increase in cytosine at 0FD sites with exposure time, which is explicable as the result of biased usage of 4FD codons. The same analysis was applied to a recently sequenced mitochondrial genome of Mytilus trossulus and produced similar results. These results are consistent with the asymmetrical model of replication and suggest that guanine oxidation due to single-strand exposure is the main cause of regional variation of nucleotide content in Mytilus mitochondrial genomes. © 2007 Springer Science+Business Media, LLC.

Marine bivalves are sessile or sedentary as adults but have planktonic larvae which can potentially disperse over large distances. Consequently larval transport is expected to play a prominent role in facilitating gene flow and determining population structure. The sea scallop (Placopecten magellanicus) is a dioecious species with high fecundity, broadcast spawning and a c. 30-day planktonic larval stage, yet it forms discrete populations or 'beds' which have significantly different dynamics and characteristics. We analysed variation at six microsatellite loci in 12 locations throughout the geographic range of the species from Newfoundland, Canada, to New Jersey, USA. Significant differentiation was present and the maximum pairwise ? value, between one of the Newfoundland samples in the north and a sample from the southern portion of the range, was high at 0.061. Other proximate pairs of samples had no detectable genetic differentiation. Mantel tests indicated a significant isolation by distance, but only when one of the populations was excluded. A landscape genetic approach was used to detect areas of low gene flow using a joint analysis of spatial and genetic information. The two major putative barriers inferred by Monmonier's algorithm were then used to define regions for an analysis of molecular variance (amova). That analysis showed a significant but low percentage (1.2%) of the variation to be partitioned among regions, negligible variation among populations within regions, and the majority of the variance distributed between individuals within populations. Prominent currents were concordant with the demarcation of the regions, while a novel approach of using particle tracking software to mimic scallop larval dispersal was employed to interpret within-region genetic patterns.

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. © 2006 The Royal Society.

In a sperm-transmitted mtDNA of Mytilus galloprovincialis we found an insertion that is not present in the typical genome and whose origin can be explained by a sequence of three events: a tandem duplication, a nonhomologous recombination, and a deletion. Unless such events are extremely rare in this species, the identical gene arrangement of the two gender-specific genomes should imply strong selection for same gene order and size. Copyright © 2006 by the Genetics Society of America.

Wall lizards of the genus Podarcis (Sauria, Lacertidae) comprise 17 currently recognized species in southern Europe, where they are the predominant reptile group. The taxonomy of Podarcis is complex and unstable. Based on DNA sequence data the species of Podarcis falls into four main groups that have substantial geographical conherence (western island group, southwestern group, Italian group and Balkan group). The Balkan species are divided in two subgroups: the subgroup of Podarcis taurica (P. taurica, P. milensis, P. gaigeae and perhaps P. melisellensis), and the subgroup of Podarcis erhardii (P. erhardii and P. peloponnesiaca). We addressed the question of phylogenetic relations among the species of the P. taurica subgroup encountered in Greece, as they can be inferred from partial mtDNA (cyt b and 16S) sequences. Our data support the monophyly of P. taurica subgroup and suggest that P. gaigeae, P. milensis and P. melisellensis form a clade, which thereinafter connects to P. taurica. Within the previous clade, P. gaigeae is more closely related to P. milensis than to P. melisellensis. However, the specimens of P. taurica were subdivided in two different groups. The first one includes the specimens from northeastern Greece, and the other group includes the specimens from the rest of continental Greece and Ionian islands. Because the molecular clock of the cyt b and 16 rRNA genes was not rejected in our model test, it is possible to estimate times of speciation events. Based on the splitting of the island of Crete from Peloponnisos [c. 5 million years ago (Ma)], the evolutionary rate for the cyt b is 1.55% per million years (Myr) and for the 16S rRNA is 0.46% per Myr. These results suggest that the evolutionary history of P. taurica in Greece is more complex than a single evolutionary invasion. The data analysed, stress the need for a reconsideration of the evolutionary history of Greek Podarcis species and help overcome difficulties that classical taxonomy has encountered at both the species level. © 2005 Blackwell Publishing Ltd.

Wall lizards of the genus Podarcis (Sauria, Lacertidae) comprise 17 currently recognized species in southern Europe, where they are the predominant nonavian reptile group. The taxonomy of Podarcis is complex and unstable. Based on DNA sequence data, the species of Podarcis falls into four main groups that have substantial geographic coherence (Western island group, southwestern group, Italian group, and Balkan Peninsula group). The Balkan Peninsula species are divided into two subgroups: the subgroup of P. taurica (P. taurica, P. milensis, P. gaigeae, and perhaps P. melisellensis), and the subgroup of P. erhardii (P. erhardii and P. peloponnesiaca). In the present study, the question of phylogenetic relationships among the species of Podarcis encountered in the Balkan Peninsula was addressed using partial mtDNA sequences for cytochrome b (cyt b) and 16S rRNA (16S). The data support the monophyly of Podarcis and suggest that there are three phylogenetic clades: the clade A (P. taurica, P. gaigeae, P. milensis, and P. melisellensis); the clade B (P. erhardii and P. peloponnesiaca), and the clade C (P. muralis and P. sicula). By examining intraspecific relationships it was found that extant populations of P. erhardii are paraphyletic. Furthermore, subspecies previously defined on the basis of morphological characteristics do not correspond to different molecular phylogenetic clades, suggesting that their status should be reconsidered. The distinct geographic distribution of the major clades of the phylogenetic tree and its topology suggest a spatial and temporal sequence of phylogenetic separations that coincide with some major paleogeographic separations during the geological history of the Aegean Sea. The results stress the need for a reconsideration of the evolutionary history of Balkan Podarcis species and help overcome difficulties that classical taxonomy has encountered at both the species and subspecies level. © 2005 Elsevier Inc. All rights reserved.

The maternal (F) and paternal (M) mitochondrial genomes of the mussel Mytilus galloprovincialis have diverged by about 20% in nucleotide sequence but retained identical gene content and gene arrangement and similar nucleotide composition and codon usage bias. Both lack the ATPase8 subunit gene, have two tRNAs for methionine and a longer open-reading frame for cox3 than seen in other mollusks. Between the F and M genomes, tRNAs are most conserved followed by rRNAs and protein-coding genes, even though the degree of divergence varies considerably among the latter. Divergence at nad3 is exceptionally low most likely because this gene includes the origin of transcription of the lagging strand (OL). Noncoding regions are the least conserved with the notable exception of the central domain of the main control region and a segment of another noncoding region immediately following nad3. The amino acid divergence (14%) of the two genomes is smaller than in two other pairs of conspecific genomes that are available in GenBank, that of the clam Venerupis philippinarum (34%) and of the fresh water mussel Inversidens japanensis (50%), suggesting that doubly uniparental inheritance of mtDNA emerged at different times in the three species or that there has been a relatively recent replacement of the male genome by the female in the Mytilus line. The latter hypothesis is supported from phylogenetic and population studies of Mytilidae. That the M genome contains a full complement of genes with no premature termination codons argues against it being a selfish element that rides with the sperm. It is shorter than the F by 118 bp, which apparently cannot account for the postulated replicative advantage of this genome over the F in male gonads. The high similarity of the two genomes explains why the F genome may assume the role of the M genome, but it does not exclude the possibility that for this to happen some M-specific sequences must be transferred on to the F genome by means of recombination. If such sequences exist they would most likely be located in noncoding regions. © Society for Molecular Biology and Evolution 2005; all rights reserved.

Both the maternal (F-type) and paternal (M-type) mitochondrial genomes of the Mytilus species complex AT edulis/galloprovincialis contain a noncoding sequence between the l-rRNA and the tRNA(Tyr) genes, here called the large unassigned region (LUR). The LUR, which is shorter in M genomes, is capable of forming secondary structures and contains motifs of significant sequence similarity with elements known to have specific functions in the sea urchin and the mammalian control region. Such features are not present in other noncoding regions of the F or M Mytilus mtDNA. The LUR can be divided on the basis of indels and nucleotide variation in three domains, which is reminiscent of the tripartite structure of the mammalian control region. These features suggest that the LUR is the main control region of the Mytilus mitochondrial genome. The middle domain has diverged by only 1.5% between F and M genomes, While the average divergence over the whole molecule is similar to20%. In contrast, the first domain is among the most divergent parts of the genome. This suggests that different parts of the LUR are under different selection constraints that are also different from those acting on the coding parts of the molecule.

Erhard's wall lizard, Podarcis erhardii (Sauria: Lacertidae), is highly diversified in Greece and especially in the southern Aegean region. Out of the 28 recognized subspecies, 27 are found in Greece from the North Sporades island-complex in the North Aegean (grossly south of the 39th parallel) to the island of Crete in the South. The species exhibits great morphological and ecological plasticity and inhabits many different habitats from rocky islets and sandy shores to mountaintops as high as 2000 m. By examining intraspecific variability at a segment of the mitochondrial gene cytochrome b we have found that that extant populations of P. erhardii are paraphyletic. Furthermore, we have found that subspecies previously defined on the basis of morphological characteristics do not correspond to different molecular phylogenetic clades, so that their status should be reconsidered. The DNA based biogeographical and phylogenetic history of Podarcis in Southern Greece is congruent with available paleogeographic data of the region, which supports the view that DNA sequences may be a useful tool for the study of palaeogeography. © 2003 Elsevier Science (USA). All rights reserved.

A partial sequence of cytochrome b (228 bp) gene of mitochondrial DNA was successfully determined from rib bones of the dwarf elephant Palaeoloxodon antiquus falconeri BUSK, which were excavated from Charkadio cave of the island of Tilos, Dodekanisa, Greece. This is the first report of DNA sequence of a dwarf elephant. The sequences were used to examine the phylogenetic relationships among Elephantidae. Phylogenetic trees reconstructed by the neighbor-joining and maximum parsimony methods provided identical topologies. The results support the "Palaeoloxodon-Elephas" clade, which is consistent with previous morphological reports according to which Palaeoloxodon is more closely related to Elephas than to Loxodonta or Mammuthus.

Cette communication montre une évaluation comparative des différentes techniques largement utilisées en génétique des populations. Dans un premier temps, nous dressons la liste des différents types de marqueurs en même temps que nous considérons leurs avantages et désavantages respectifs. Ensuite, nous présentons des exemples de leur utlisation à partir de nos travaux : polymorphisme de réaction antigène anticorps, allozymes, marqueurs nucléaires anonymes, polymorphisme d'amplification aléatoire, minisatellites, microsatellites, variation de l'ADN mitochondrial, RFLP, SSCP, séquençage. Le choix du marqueur dépendra de la question particulière à laquelle on veut répondre : hétérozygotie et sélection versus dérive génétique dans les populations naturelles, marqueurs génétiques pour les recherches en aquaculture. Des exemples de nos propres travaux qui illustrent ces points sont présentés. (Résumé d'auteur)