Presence of a unique male-specific extension of C-terminus to the cytochrome c oxidase subunit II protein coded by the male-transmitted mitochondrial genome of Venustaconcha ellipsiformis (Bivalvia: Unionoidea)

Analyses of unionoidean bivalve male-transmitted (M) mtDNA genomes revealed an approximately 555 bp 3' coding extension to cox2. An antibody was generated against this predicted C-terminus extension to determine if the unique cox2 protein is expressed. Western blot and immunohistochemistry analyses demonstrated that the protein was predominantly expressed in testes. Weak expression was detected in other male tissues but the protein was not detected in female tissues. This is the first report documenting the expression of a cox2 protein with a long C-terminus in animals. Its universal presence in unionoidean bivalve testes suggests a functional significance for the protein.

Comparative analysis of gender-associated complete mitochondrial genomes in marine mussels (Mytilus spp.)

Marine mussels of the genus Mytilus have an unusual mode of mitochondrial DNA (mtDNA) transmission termed doubly uniparental inheritance (DUI). Female mussels are homoplasmic for the F mitotype, which is inherited maternally, while males are usually heteroplasmic, carrying a mixture of the maternal F mitotype and the paternally inherited M genome. Two classes of M genomes have been observed: "standard" M genomes and "recently masculinized" M genomes. The latter are more similar to F genomes at the sequence level but are transmitted paternally like standard M genomes. In this study we report the complete sequences of two standard male M. edulis and one recently masculinized male M. trossulus mitochondrial genome. A comparative analysis, including the previously sequenced M. edulis F and M. galloprovincialis F and M mtDNAs, reveals that these genomes are identical in gene order, but highly divergent in nucleotide and amino acid sequence. The large amount (>20%) of nucleotide substitutions that fall in coding regions implies that there are several amino acid replacements between the F and M genomes, which likely have an impact on the structural and functional properties of the mitochondrial proteome. Correlation of the divergence rate of different protein-coding genes indicates that mtDNA-encoded proteins of the M genome are still under selective constraints, although less highly than genes of the F genome. The mosaic F/M control region of the masculinized F genome provides evidence for lineage-specific sequences that may be responsible for the different mode of transmission genetics. This analysis shows the value of comparative genomics to better understand the mechanisms of maintenance and segregation of mtDNA sequence variants in mytilid mussels.

Mitochondrial DNA polymorphisms and sperm motility in Mytilus edulis (Bivalvia: Mytilidae)

The system of mitochondrial DNA (mtDNA) inheritance in Mytilus and other bivalves, termed doubly uniparental inheritance (DUI), is novel among animals. Males pass on their male transmitted (M-type) mtDNA from fathers to their sons whereas females pass on their female transmitted (F-type) mtDNA from mothers to both sons and daughters. Thus, Mytilus males contain two distinct types of mtDNA. Interestingly, sperm contains only the paternal mtDNA. Phylogenetic analysis has shown that some female types have been able to switch their route of inheritance. These "recently masculinized" mitochondrial genomes behave as a typical M-type in that they are transmitted from generation to generation through sperm. Because the "recently masculinized" and "standard" male mitotypes in M. edulis exhibit approximately 8.7% amino acid sequence divergence, we hypothesized that these differences could affect mitochondrial, and hence sperm, functions. Furthermore, since recently masculinized mitotypes have been shown to replace standard male types periodically over evolutionary timescales, we tested the hypothesis that sperm swimming speeds would be greater for males with recently masculinized M-type genomes. Sperm activity was videotaped, digitized and tracked. A linear mixed effects model found no significant difference in linear velocities or curvilinear speeds between the mitotypes suggesting that swimming speeds are similar for both in the period shortly after spawning.

High fidelity of mitochondrial genome transmission under the doubly uniparental mode of inheritance in freshwater mussels (Bivalvia: Unionoidea)

Doubly uniparental inheritance (DUI) of mitochondrial DNA (mtDNA) has been demonstrated in both mytilid and unionid bivalves. Under DUI, females pass on their mtDNA to both sons and daughters, whereas males pass on their mtDNA to only sons. In mytilids, the loss of an original male (or M) mitotype, with its subsequent replacement by that lineage's female (or F) mitotype, has been called a role-reversal or, more specifically, a masculinization event. Multiple masculinization events have been inferred during the evolutionary history of mytilids but not unionids. The perceived lack of role-reversal events in unionids may represent a significant difference in the evolutionary dynamics of DUI between the two bivalve taxa or simply a lack of sufficient taxon sampling in unionids. To evaluate these alternative hypotheses, six additional unionoidean bivalve genera were sampled for DUI including one genus from the sister taxon of the Unionidae, the Hyriidae. Phylogenetic analyses of 619 base pairs of cytochrome c oxidase I (COI) from eight genera (nine species) of unionoidean bivalves, plus the sister taxon to the Unionoida, Neotrigonia, revealed that the M and F unionoidean mitotypes were contained in gender-specific, topologically congruent clades. This supports the hypothesis that either role-reversal events do not occur in unionoideans or, if they do occur, their products are ephemeral in an evolutionary sense. Furthermore, the fact that the mantle-tissue-derived Neotrigonia mitotype is the sister mitotype to the unionoidean F mitotype clade suggests that DUI has been operating with high fidelity in unionoids for at least 200 million years. A relatively low incidence of interspecific hybridization in unionoideans and a possibly obligate role for the M mitotype in unionoidean gender determination are offered as potential explanations for the disparate evolutionary dynamics of DUI observed between mytilid and unionoidean bivalves.

Tissue-specific expression of male-transmitted mitochondrial DNA and its implications for rates of molecular evolution in Mytilus mussels (Bivalvia: Mytilidae)

Mytilus and other bivalves exhibit an unusual system of mitochondrial DNA (mtDNA) transmission termed doubly uniparental inheritance (DUI). Specifically, males transmit the mtDNA they have received from their fathers to their sons. Females transmit their mother's mtDNA to both sons and daughters. Males are normally heteroplasmic and females are normally homoplasmic, but not exclusively. This system is associated with an unusual pattern of molecular evolution. Male-transmitted mtDNA (M type) evolves faster than female-transmitted (F type) mtDNA. Relatively relaxed selection on the M type has been proposed as an explanation for this phenomenon. To further evaluate the selective forces acting upon the M-type genome, we used RT-PCR to determine where it is expressed. M-type mtDNA expression was detected in all gonad samples and in 50% of somatic tissues of males, and in a single female tissue. F-type mtDNA expression was detected in all female tissues, all male somatic tissues, and all but one male gonad sample. We argue that the expression of M-type mtDNA in male somatic and male gonad tissues has implications for the strength of selection acting upon it.

The maritime shrew, Sorex maritimensis (Insectivora: Soricidae): a newly recognized Canadian endemic

Previous morphological and cytological analyses have suggested that the arctic shrew (Sorex arcticus) as currently recognized may be two distinct species. Specifically, those studies demonstrated considerable differentiation between the putative subspecies S. a. maritimensis and one or both of the other two subspecies, S. a. arcticus and S. a. laricorum. Phylogenetic analysis of 546 base pairs of cytochrome b sequence data from 10 arctic shrews from across Canada indicates that maritimensis is the sister-group to arcticus + laricorum. Furthermore, there is considerable genetic divergence between maritimensis and the other two putative subspecies (~8–9%; Kimura's two-parameter distance). Given that maritimensis and arcticus + laricorum appear to be reciprocally monophyletic clades with considerable genetic divergence (i.e., greater than that between other recognized pairs of sister-species within the S. araneus–arcticus group), we propose that S. maritimensis be recognized as a distinct species. The proportion of third-position transversion substitutions between S. arcticus and S. maritimensis suggests that these two species shared a common ancestor approximately 2.4 million years ago.

Molecular phylogeny and evolution of Sorex shrews (Soricidae: insectivora) inferred from mitochondrial DNA sequence data

Shrews of the genus Sorex are characterized by a Holarctic distribution, and relationships among extant taxa have never been fully resolved. Phylogenies have been proposed based on morphological, karyological, and biochemical comparisons, but these analyses often produced controversial and contradictory results. Phylogenetic analyses of partial mitochondrial cytochrome b gene sequences (1011 bp) were used to examine the relationships among 27 Sorex species. The molecular data suggest that Sorex comprises two major monophyletic lineages, one restricted mostly to the New World and one with a primarily Palearctic distribution. Furthermore, several sister-species relationships are revealed by the analysis. Based on the split between the Soricinae and Crocidurinae subfamilies, we used a 95% confidence interval for both the calibration of a molecular clock and the subsequent calculation of major diversification events within the genus Sorex. Our analysis does not support an unambiguous acceleration of the molecular clock in shrews, the estimated rate being similar to other estimates of mammalian mitochondrial clocks. In addition, the data presented here indicate that estimates from the fossil record greatly underestimate divergence dates among Sorex taxa.

The distribution of male-transmitted and female-transmitted mitochondrial DNA types in somatic tissues of blue mussels: Implications for the operation of doubly uniparental inheritance of mitochondrial DNA

We have examined the mitochondrial DNA (mtDNA) content of several somatic tissues from male and female individuals of the blue mussel, Mytilus edulis. As expected from the mode of doubly uniparental inheritance (DUI) of mtDNA that is characteristic of this genus, the dominant type of mtDNA in male gonads was the male-transmitted M type. In contrast, all male somatic tissues were dominated by the female-transmitted F type. The M type could occasionally be detected in one or another tissue of a few female individuals. The findings have several implications for the operation of doubly uniparental inheritance of mitochondrial DNA, among which the most important are (i) the M genome does not have an unconditional replicative advantage over the F genome, and (ii) in contrast to "masculinization" (the process by which an F molecule assumes the role of the M genome) "feminization" (the process by which an M molecule assumes the role of the F genome) might be a rare but not impossible phenomenon.Key words: mitochondrial DNA inheritance, mitochondrial DNA tissue distribution, blue mussels, gender-specific mtDNA, doubly uniparental inheritance of mtDNA, Mytilus.

Phylogenetic evidence for role-reversals of gender-associated mitochondrial DNA in Mytilus (Bivalvia: Mytilidae)

Distinct gender-associated mitochondrial DNA (mtDNA) lineages (i.e., lineages which are transmitted either through males or through females) have been demonstrated in two families of bivalves, the Mytilidae (marine mussels) and the Unionidae (freshwater mussels), which have been separated for more than 400 Myr. The mode of transmission of these M (for male-transmitted) and F (for female-transmitted) molecules has been referred to as doubly uniparental inheritance (DUI), in contrast to standard maternal inheritance (SMI), which is the norm in animals. A previous study suggested that at least three origins of DUI are required to explain the phylogenetic pattern of M and F lineages in freshwater and marine mussels. Here we present phylogenetic evidence based on partial sequences of the cytochrome c oxidase subunit I gene and the 16S RNA gene that indicates the DUI is a dynamic phenomenon. Specifically, we demonstrate that F lineages in three species of Mytilus mussels, M. edulis, M. trossulus, and M. californianus, have spawned separate lineages which are now associated only with males. This process is referred to as "masculinization" of F mtDNA. By extension, we propose that DUI may be a primitive bivalve character and that periodic masculinization events combined with extinction of previously existing M types effectively reset the time of divergence between conspecific gender-associated mtDNA lineages.

Degree of selective constraint as an explanation of the different rates of evolution of gender-specific mitochondrial DNA lineages in the mussel mytilus

Mussels of the genus Mytilus segregate for a maternally transmitted F lineage and a paternally transmitted M lineage of mitochondrial DNA. Previous studies demonstrated that these lineages are older than the species of the M. edulis complex and that the M lineage evolves faster than the F lineage. Here we show that the latter observation also applies to a region of the molecule with no assigned function. Sequence data for the mitochondrial COIII gene and the "unassigned" region of the F and M lineages of M. edulis and M. trossulus are used to evaluate various hypotheses that may account for the faster rate of evolution of the M lineage. Tests based on the proportion of synonymous and nonsynonymous substitutions suggest that the M lineage experiences relatively relaxed selection. Further support for this hypothesis comes from an examination of COIII amino acid substitutions at sites defined as either conserved or variable based on the pattern of variation in other mollusks and Drosophila. Most substitutions in the M lineage occur in regions that are also variable among non-Mytilus taxa. We suggest that these differences in selection pressure are a consequence of doubly uniparental mitochondrial DNA transmission in Mytilus.

Species-specific segregation of gender-associated mitochondrial DNA types in an area where two mussel species (Mytilus edulis and M. trossulus) hybridize

In each of the mussel species Mytilus edulis and M. trossulus there exist two types of mtDNA, the F type transmitted through females and the M type transmitted through males. Because the two species produce fertile hybrids in nature, F and M types of one may introgress into the other. We present the results from a survey of a population in which extensive hybridization occurs between these two species. Among specimens classified as "pure" M. edulis or "pure" M. trossulus on the basis of allozyme analysis, we observed no animal that carried the F or the M mitotype of the other species. In most animals of mixed nuclear background, an individual's mtDNA came from the species that contributed the majority of the individual's nuclear genes. Most importantly, the two mtDNA types in post-F1 male hybrids were of the same species origin. We interpret this to mean that there are intrinsic barriers to the exchange of mtDNA between these two species. Because such barriers were not noted in other hybridizing species pairs (many being even less interfertile than M. edulis and M. trossulus), their presence in Mytilus could be another feature of the unusual mtDNA system in this genus.

Male and female mitochondrial DNA lineages in the blue mussel (Mytilus edulis) species group

In blue mussels of the Mytilus edulis species complex, mitochondrial DNA (mtDNA) inheritance is coupled with gender. Females receive their mother's mtDNA and pass it on to both their daughters and sons. In addition, males receive mtDNA from their father and transmit this male mtDNA to their sons. If this pattern of "doubly uniparental inheritance" is older than the M. edulis species complex, then all members of this group must have two distinct mtDNA lineages: a maternal lineage that is transmitted through females and a paternal lineage that is transmitted through males. To test this hypothesis, we scored mtDNA variation in two taxa in this complex, M. edulis and M. trossulus, by means of restriction fragment profiles of whole-mtDNA genomes and DNA sequence of a region of the cytochrome c oxidase subunit III gene (COIII). The various mitotypes present in these mussels were classified as "male" or "female" based on their gender association and as belonging to M. edulis or M. trossulus based on species-specific allozymes. Both maximum parsimony and neighbor-joining phylogenies based on the COIII sequences grouped female and male mtDNAs into two distinct lineages irrespective of specific origin in accordance with the hypothesis that the origin of these lineages predates the divergence of M. edulis and M. trossulus.

Evolution of mtDNA D-loop sequences and their use in phylogenetic studies of shrews in the subgenus Otisorex (Sorex: Soricidae: Insectivora)

mtDNA D-loop sequences were examined in shrews of the genus Sorex. All specimens possessed an array of tandem repeats in which each repeat was 78 to 80 base pairs (bp) in length. Each specimen also possessed a 76-bp imperfect copy of the tandem repeats. Three observations are consistent with the tandem repeats being the product of concerted evolution: (1) the repeats are capable of forming secondary structures; (2) there was minimal sequence divergence between tandem repeats within individuals; and (3) although the tandem repeats and the imperfect repeat presumably arose due to a duplication event in an ancestor of the shrews, the imperfect repeat per se was not copied in any of the specimens observed. Interspecific homology can therefore be assumed for the imperfect repeat. Furthermore, given the apparent high rate of concerted evolution within a genome, tandem repeats in different individuals may be compared as though only a single copy were present. By including data from the imperfect repeat, the last tandem repeat, and the surrounding unique sequence cladistic and genetic distance approaches to phylogeny reconstruction indicated two sister groups within the subgenus Otisorex. One group was composed of Sorex fumeus and the S. cinereus species complex and the other group was composed of S. hoyi, S. monticolus, S. vagrans, and S. palustris. Resolution of relationships among recently evolved taxa demonstrated the usefulness of selected regions of the D-loop for molecular systematic studies.

Patterns of sequence variation in the mitochondrial D-loop region of shrews

Direct sequencing of the mitochondrial displacement loop (D-loop) of shrews (genus Sorex) for the region between the tRNA(Pro) and the conserved sequence block-F revealed variable numbers of 79-bp tandem repeats. These repeats were found in all 19 individuals sequenced, representing three subspecies and one closely related species of the masked shrew group (Sorex cinereus cinereus, S. c. miscix, S. c. acadicus, and S. haydeni) and an outgroup, the pygmy shrew (S. hoyi). Each specimen also possessed an adjacent 76-bp imperfect copy of the tandem repeats. One individual was heteroplasmic for length variants consisting of five and seven copies of the 79-bp tandem repeat. The sequence of the repeats is conducive to the formation of secondary structure. A termination-associated sequence is present in each of the repeats and in a unique sequence region 5' to the tandem array as well. Mean genetic distance between the masked shrew taxa and the pygmy shrew was calculated separately for the unique sequence region, one of the tandem repeats, the imperfect repeat, and these three regions combined. The unique sequence region evolved more rapidly than the tandem repeats or the imperfect repeat. The small genetic distance between pairs of tandem repeats within an individual is consistent with a model of concerted evolution. Repeats are apparently duplicated and lost at a high rate, which tends to homogenize the tandem array. The rate of D-loop sequence divergence between the masked and pygmy shrews is estimated to be 15%-20%/Myr, the highest rate observed in D-loops of mammals. Rapid sequence evolution in shrews may be due either to their high metabolic rate and short generation time or to the presence of variable numbers of tandem repeats.

Sexual dimorphism in thick-billed murres, Uria lomvia

The pattern of sexual dimorphism in thick-billed murres, Uria lomvia, from the Lancaster Sound – Jones Sound region, Northwest Territories, was examined for weight and 21 skeletal characters. Univariate statistics (Bonferroni-corrected t-tests) indicated that males were significantly larger than females in 6 bill and skull characters. Multivariate statistics also indicated that males had larger bills and skulls than females (based on canonical discriminant analysis), but males were not larger than females in overall body size (as defined by the first principal-components axis). The direction and magnitude of dimorphism were consistent with a hypothesis based on sexual selection as the driving force. In particular, large bill and skull sizes in males are consistent with agonistic behaviours associated with male–male competition for breeding sites and mate guarding.

Genetic differentiation and biogeography of the masked shrew in Atlantic Canada

The masked shrew (Sorex cinereus) occurs naturally on a number of small to large islands in Atlantic Canada, and 22 individuals were introduced into Newfoundland from New Brunswick in 1958. Genetic variation detected by protein electrophoresis of 34 presumptive gene loci was assayed in five island and three mainland populations from this region to compare rates of differentiation among the populations and to investigate genetic relationships among populations in the context of historical biogeographic events constructed from the geological literature. We found considerable differentiation among populations which can be attributed to different origins for the populations in the post-Wisconsin glacial phase, and to apparently rapid evolution in small isolated populations, especially for the small island of Bon Portage, Nova Scotia. Allele frequencies are more heterogeneous among the island populations and exhibit classic neutral behaviour in that rare allelles are absent and shifts in allele frequency occur to either side of mainland means. There is no correlation of allele frequencies with geographic proximity of populations as might be expected under selectively based clines, or, alternatively, under isolation by distance expected with a diffusive wave of colonization in the region. Instead, the genetic data are compatible with random drift of neutral alleles in populations of various efffective sizes isolated from each other by rising sea levels in the last 20 000 – 5000 years. The considerable divergence that has occurred among the island populations (FST = 0.238) may be indicative of incipient speciation or subspeciation. This subdivision does not appear to be founder-induced but is more likely the product of gradual drift in and interruption of homogenizing gene flow among relict populations that existed during the Pleistocene.

Prostate-specific antigen levels from completely sectioned, clinically benign, whole prostates

Clinically benign whole, untrimmed prostates and pelvic lymph nodes were obtained from 105 patients at autopsy. All 105 patients had premortem serum from which prostate-specific antigen (PSA) levels were obtained. Sixty-eight did not have carcinoma of the prostate (CAP), 28 had CAP less than 1 ml and 9 had CAP larger than 1 ml. Eleven untrimmed prostates weighed 80 g or more and eight had elevated PSA levels (more than 4.0 ng/ml): five of eight without CAP, two of two with CAP less than 1 ml, and one of one with CAP larger than 1 ml. Ninety-four whole untrimmed prostates weighed less than 80 g and 20 had elevated PSA levels: ten of 60 without CAP, two of 26 with CAP less than 1 ml, and eight of eight with CAP larger than 1 ml. This study suggests that PSA levels from patients with untrimmed prostates weighing 80 g or more (equivalent to a 60-g trimmed prostate) are usually elevated regardless whether CAP is present. However, CAP less than 1 ml, in untrimmed prostates less than 80 g, usually does not elevate PSA levels whereas CAP larger than 1 ml usually does (P less than 0.0001). The likelihood that elevated PSA levels, from patients with untrimmed prostates less than 80 g, are due to CAP larger than 1 ml increases as the PSA level increases.

Nerve conduction velocity in hypertensive patients

Due to conflicting reports in the literature regarding nerve conduction velocities (NCVs) in hypertensives, peroneal and sural NCVs and facial nerve conduction latencies were studied in 30 hypertensives and in 30 controls. An improved technique of NCV measurement was used. Twenty-one of the hypertensives were retested after five weeks, and five of them were tested for motor and sensory NCVs of the median nerve during a short period of partial occlusion of blood flow in the arm. No changes were found that could be related to blood pressure, duration of hypertension, eyeground changes, or partial restriction of blood flow.

Primary aldosteronism. A study in contrasts

Two patient with primary aldosteronism, one with a solitary adrenal adenoma and the other with bilateral nodular hyperplasia, are described. Both patients showed the classic features of primary aldosteronism in electrolyte and hormone patterns, but there were important differences in the biochemistry of their excised adrenal tissue. In addition, the injection of plasma from the patient with bilateral adrenal hyperplasia into the sheep's transplanted adrenal gland elicited a definite aldosterone secretory response, but there was no aldosterone response to the injection of plasma from the patient with a solitary adrenal adenoma. The findings support the hypothesis that an extra-adrenal stimulus may contribute to the pathogenesis of bilateral adrenal hyperplasia.