Genetic differentiation of Mediterranean horse mackerel (Trachurus mediterraneus) populations as revealed by mtDNA PCR-RFLP analysis

The genetic population structure of Mediterranean horse mackerel, Trachurus mediterraneus , from seven locations throughout the Black, Marmara, Aegean and eastern Mediterranean seas was investigated using restriction fragment length polymorphism (RFLP) analysis of the mtDNA 16S rDNA region. An approximately 2000-bp segment was screened in 280 individuals using six restriction enzymes, resulting in 10 composite haplotypes. The most common haplotype was present in 56.42% individuals; the next most frequent haplotype was present in 22.85% individuals. Average haplotype diversity within samples was moderate (0.38), and nucleotide diversity was low (0.00435). Mean nucleotide divergence for the seven sampling sites was 0.0028. Nucleotide divergence among samples was moderate, with the highest value detected between the Aegean Sea (Izmir) and the eastern Black Sea (Trabzon) populations (0.007055), and the lowest (−0.000043) between the Marmara Sea (Adalar) and the western Black Sea (Sile) populations. In Monte Carlo pairwise comparisons of haplotype frequencies, the Sinop from the middle Black Sea, Trabzon from the eastern Black Sea, and Iskenderun Bay from the north-eastern Mediterranean Sea exhibited highly significant (P   <   0.001) geographical differentiation from each other and from all other populations. Mantel's test indicated that the nucleotide divergence among populations of T. mediterraneus was not significantly associated with their geographical isolation ( r  = −0.2963; P   >   0.05). Consequently, the mtDNA 16S rDNA region provided evidence for the existence of three distinct T. mediterraneus populations (Sinop, Trabzon and Iskenderun Bay) in the Black and north-eastern Mediterranean seas.     

Taxonomic relationships within the pan-oriental narrow-mouth toad Microhyla ornata as revealed by mtDNA analysis (Amphibia, Anura, Microhylidae)

A molecular phylogenetic survey was conducted using mtDNA sequences of 12S and 16S rRNA, and cyt-b genes to examine taxonomic relationships among populations of the Pan-Oriental microhylid, Microhyla ornata, from India, Bangladesh, Thailand, Laos, China, Taiwan, and the Ryukyu Archipelago of Japan. Two discrete clades are recognized within this species, one consisting of populations from India and Bangladesh, and the other encompassing the remaining populations. In the latter clade, populations from the Ryukyu Archipelago are clearly split from the rest (populations from Taiwan and the continent) with considerable degrees of genetic differentiations. Each of the three lineages is judged to represent a good species, and the name Microhyla ornata is restricted to the South Asian populations. For the populations from Taiwan and a wide region from China to Southeast Asia, the name Microhyla fissipes should be applied, whereas the Ryukyu populations are most appropriately referred to as Microhyla okinavensis, although further substantial genetic differentiations are recognized among some island group populations within this last species.     

History of Lipizzan horse maternal lines as revealed by mtDNA analysis

Sequencing of the mtDNA control region (385 or 695 bp) of 212 Lipizzans from eight studs revealed 37 haplotypes. Distribution of haplotypes among studs was biased, including many private haplotypes but only one haplotype was present in all the studs. According to historical data, numerous Lipizzan maternal lines originating from founder mares of different breeds have been established during the breed''s history, so the broad genetic base of the Lipizzan maternal lines was expected. A comparison of Lipizzan sequences with 136 sequences of domestic- and wild-horses from GenBank showed a clustering of Lipizzan haplotypes in the majority of haplotype subgroups present in other domestic horses. We assume that haplotypes identical to haplotypes of early domesticated horses can be found in several Lipizzan maternal lines as well as in other breeds. Therefore, domestic horses could arise either from a single large population or from several populations provided there were strong migrations during the early phase after domestication. A comparison of Lipizzan haplotypes with 56 maternal lines (according to the pedigrees) showed a disagreement of biological parentage with pedigree data for at least 11% of the Lipizzans. A distribution of haplotype-frequencies was unequal (0.2%–26%), mainly due to pedigree errors and haplotype sharing among founder mares.     

Phylogeography and sympatric differentiation of the Arctic charr Salvelinus alpinus (L.) complex in Siberia as revealed by mtDNA sequence analysis

Sequence variation in the mtDNA control region of Arctic charr Salvelinus alpinus and Dolly Varden Salvelinus malma from 56 Siberian and North American populations was analysed to assess their phylogeographic relationships and the origins of sympatric forms. Phylogenetic trees confirm the integrity of phylogroups reported in previous mtDNA studies except that the Siberian group does not separate as a single cluster. Haplotype network analysis indicates the proximity of Siberian and Atlantic haplotypes. These are considered as one Eurasian group represented by the Atlantic, east Siberian (interior Siberia including Transbaikalia, Taimyr) and Eurosiberian (Finland, Spitsbergen, Taimyr) sub-groups. Salvelinus alpinus with presumably introgressed Bering group (malma) haplotypes were found along eastern Siberian coasts up to the Olenek Bay and the Lena Delta region, where they overlap with the Eurasian group and in the easternmost interior region. It is proposed that Siberia was colonized by S. alpinus in two stages: from the west by the Eurasian group and later from the east by the Bering group. The high diversity of Eurasian group haplotypes in Siberia indicates its earlier colonization by S. alpinus as compared with the European Alps. This colonization was rapid, proceeded from a diverse gene pool, and was followed by differential survival of ancestral mtDNA lineages in different basins and regions, and local mutational events in isolated populations. The results presented here support a northern origin of Transbaikalian S. alpinus , the dispersion of S. alpinus to the Lake Baikal Basin from the Lena Basin, segregation of S. alpinus between Lena tributaries and their restricted migration over the divides between sub-basins. These results also support sympatric origin of intralacustrine forms of S. alpinus .     

Genetic variation among Mediterranean populations of Sesamia nonagrioides (Lepidoptera: Noctuidae) as revealed by RFLP mtDNA analysis

Restriction fragment length polymorphism analysis of two segments of mitochondrial DNA (COI and 16S rRNA) was used to examine genetic variation in Sesamia nonagrioides (Lefèbvre) populations from the Mediterranean basin. Four populations were collected from central and southern Greece, and five from northern latitudes: Greece, Italy, France and Spain. No variation was observed in COI, while 16S rRNA segment proved highly polymorphic and 28 different haplotypes were found. Lower intra-population polymorphism was found in the northern populations than in southern ones. Although no significant isolation by distance was found, the UPGMA tree based on Nei's raw number of nucleotide differences separated the populations into two major groups, i.e. one with the northern (40.6 degrees N-43.4 degrees N) and the other with the southern populations (37.3 degrees N-39.2 degrees N). Analysis of molecular variance revealed that most of the variation was between the two major groups (Phi(CT)=0.559), and all pairwise comparisons between the northern and southern populations resulted in high and significant F(ST) values (overall F(ST)=0.604). The high F(ST) values and the strong spatial genetic structure indicate that long-distance migration may be a rare event. The populations do not seem to have experienced a strong historical bottleneck. The occurrence of a few widespread haplotypes and the genetic similarity of the northern populations could be attributed to a historical expansion of certain haplotypes from the south towards to the northern borders of the species' distribution area.     

Genomic relationships within Boronia (Rutaceae) as revealed by karyotype analysis and RAPD molecular markers

 The genus Boronia Sm. section Boronia series Boronia contains species with n=7 (B. megastigma), n=7 or 8 (B. heterophylla), n=8 (B. molloyae) and n=9 (B. purdieana), representing ideal species with which to examine comparative chromosome morphology. Between species there were few chromosomes with similar morphology, indicating numerous genome re-organisations. Karyotypes between and within species of Boronia could be distinguished and inheritance of some chromosomes was observed. Species and hybrids with 2n = 14 or 15 had at least one large chromosome. Chromosome morphology indicated a closer relationship between B. heterophylla and B. molloyae and between B. purdieana and B. megastigma than between these two groups. Whole genomic DNA was extracted from 9 genotypes of Boronia. RAPD bands were analysed and pairwise distance matrices between genotypes were computed. Dendrograms were generated and analysed using unweighted pair-group method with arithmetic average cluster analysis. Dendograms supported cytological results, indicating B. heterophylla and B. molloyae are closely related and clearly distinct from B. megastigma and B. purdieana. The evolution of boronias is discussed. Received February 16, 2001; accepted March 21, 2002 Published online: October 14, 2002 Address of the authors: G. Yan, F. Shan, J. A. Plummer (e-mail: jplummer@cyllene.uwa.edu.au), Plant Sciences, Faculty of Natural and Agricultural Science, The University of Western Australia, 35 Stirling Hwy, Crawley, WA 6009, Australia.     

Bank voles in linear habitats show restricted gene flow as revealed by mitochondrial DNA (mtDNA)

Genetic structure of bank vole populations in linear river bank habitat in southeast Norway was determined from analyses of DNA sequences for the mitochondrial D-loop. Animals were sampled at sites separated by 1 km, along two forested river banks separated by ≈ 100 m of open water. Twenty-six distinct haplotypes were found among 120 voles. The voles showed significant deviation from panmixis on both sides of the river. Animals from the same site or from sites 1 km apart were more likely to share haplotypes than animals 2 km apart or more. Common haplotypes were widespread on both river banks, and had a wider distribution than relatively rare haplotypes. Some rare haplotypes were found on both banks, but most were restricted to a single bank. The results suggest that short-term gene flow may be restricted for female bank voles in linear habitats. Female territorial behaviour may vary with habitat geometry. In the linear habitat described here, females defend only two territorial borders and may effectively limit female dispersal. Results were compared to a previous study of bank voles from this region in a two-dimensional habitat. Gene flow in the linear habitat was much more restricted than gene flow in the two-dimensional habitat. Probable mechanisms underlying this difference are discussed.     

Genetic diversity and differentiation in Dalbergia sissoo (Fabaceae) as revealed by RAPD

Dalbergia sissoo, a wind-dispersed tropical tree, is one of the most preferred timber tree species of South Asia. Genetic diversity and differentiation among natural populations of D. sissoo were examined for the first time. We found a relatively high level of genetic diversity in D. sissoo, both at the species level (percentage of polymorphic bands = 89.11%; H = 0.2730; I = 0.4180) and the population level (percentage of polymorphic bands = 68.7%; H = 0.239; I = 0.358), along with a relatively low degree of differentiation among populations (GST = 0.1311; AMOVA = 14.69%). Strong gene flow among populations was estimated, N(m) = 3.3125. The Mantel test suggested that genetic distances between populations were weakly correlated with geographic distances (R = 0.3702, P = 0.1236). The high level of genetic diversity, low degree of differentiation, strong gene flow, and weak correlation between genetic and geographic distances can be explained by its biological character and wide-spread planting. This information will be useful for the introduction, conservation and further studies of D. sissoo and related species.     

Extensive mtDNA diversity in horses revealed by PCR–SSCP analysis

The hypervariable D-loop region of mitochondrial DNA (mtDNA) was amplified with the polymerase chain reaction using total horse DNA samples. Analysis of single strand conformation polymorphism (SSCP) of denatured amplification products was carried out by native polyacrylamide (8%) gel electrophoresis followed by silver staining. As many as 15 distinct SSCP variants were revealed when screening a total of 78 maternally unrelated horses representing five different breeds. All breeds showed a high degree of polymorphism and the estimated probability (PI_mt) that two maternally unrelated individuals have, by chance, identical SSCP variants varied between 0.14 and 0.30. We detected no heteroplasmy or deviations from strict and stable maternal inheritance when examining four maternal lineages, each represented by six to eight horses, separated by up to five generations from a common ancestral mare. The study establishes a simple screening method for detecting equine mtDNA types, which can be applied for tracing maternal genealogies and for association studies.     

Population differentiation in the red-legged kittiwake (Rissa brevirostris) as revealed by mitochondrial DNA

Population decline in red-legged kittiwakes(Rissa brevirostris) over recent decadeshas necessitated the collection of informationon the distribution of genetic variation withinand among colonies for implementation ofsuitable management policies. Here we present apreliminary study of the extent of geneticstructuring and gene flow among the threeprincipal breeding locations of red-leggedkittiwakes using the hypervariable Domain I ofthe mitochondrial control region. Geneticvariation was high relative to other species ofseabirds, and was similar among locations.Analysis of molecular variance indicated thatpopulation genetic structure was statisticallysignificant, and nested clade analysissuggested that kittiwakes breeding on BeringIsland maybe genetically isolated from thoseelsewhere. However, phylogeographic structurewas weak. Although this analysis involved onlya single locus and a small number of samples,it suggests that red-legged kittiwakes probablyconstitute a single evolutionary significantunit; the possibility that they constitute twomanagement units requires furtherinvestigation.     

Phylogenetic relationships within the genus Citrus (Rutaceae) and related genera as revealed by RFLP and RAPD analysis

 Relationships among 88 accessions representing 45 Citrus species, three man-made hybrids, and six related genera were examined for restriction fragment length polymorphisms (RFLP). Thirty-two Citrus and three Microcitrus accessions were also examined by random amplified polymorphic DNA (RAPD) analysis. A measure of relative heterozygosity was estimated based on the mean of the number of fragments per individual per probe-enzyme combination (PEC) divided by total number of fragments per PEC for all non-hybrid Citrus individuals. The presence in a Citrus species of a rare band found also in a related genus was taken as an indication of possible introgression, while the presence of several fragments unique to 1 species was used to indicate non-involvement of that species in hybridization events. Most species that have been described in the literature as hybrids had high heterozygosity indices and no unique fragments. Distance matrices and dendrograms were generated using simple matching coefficient and neighbor-joining cluster analysis. RFLP and RAPD data gave approximately the same results. These data showed C. maxima was affiliated with the papedas C. hongheensis and C. latipes. C. medica clustered with C. indica when only non-hybrid taxa were examined, or among limes, lemons, and relatives when all species were considered. Mandarins did not show strongly supported groupings among themselves, nor with other species. These data showed that several accessions were probably assigned to the wrong species. Received: 30 September 1997 / Accepted: 29 October 1997     

Limited genetic differentiation in Labeo rohita (Hamilton 1822) populations as revealed by microsatellite markers

Labeo rohita, popularly known as rohu is a widely cultured species in the whole Indian subcontinent. Knowledge of the genetic diversity of this species is important to support management and conservation programs which will subsequently help in sustainable production of this species. DNA markers, mostly microsatellite markers are excellent tool to evaluate genetic variation of populations. Genetic variation of three wild and one farm population was assessed using eleven microsatellite loci. In analyzing 192 samples, the number of alleles ranged from 4 to 23; observed heterozygosity 0.500 to 0.870 and expected heterozygosity from 0.389 to 0.878. Exact test for Hardy Weinberg disequilibrium revealed that each riverine sample had at least one locus not in equilibrium except one river. Negative inbreeding coefficients (F_IS) were observed across populations indicating very high level of genetic diversity but little genetic differentiation among populations.     

The evolutionary history of the sinica-group of macaque monkeys as revealed by mtDNA restriction site analysis.

We estimated the phylogenetic relationships of mitochondrial DNA haplotypes within the sinica-group of macaques, which includes Macaca sinica, M. radiata, M. thibetana, M. assamensis, and possibly M. arctoides. Some effort was made to detect intraspecific variation by sampling individuals from different parts of the species' range or from different matrilines. In the case of M. assamensis, individuals were sampled from both subspecies (M. assamensis assamensis and M. assamensis pelops). Total genomic DNA was extracted from blood samples and cut with a battery of 16 restriction endonucleases. A total of 97 restriction sites were mapped for these enzymes in the sinica-group and M. nemestrina, which was used as an outgroup. Phylogenetic trees constructed by both the maximum parsimony method and the neighbor-joining method were highly congruent. A bootstrap analysis of the maximum parsimony tree indicated a high degree of confidence to the association of particular haplotypes within the 80% majority rule consensus tree. An exhaustive search of all possible trees also supported this topology, although one haplotype had to be eliminated from this analysis to save computer time. The results were also unaffected by weighting the character state changes in favor of site gains over site losses. The mtDNA phylogeny produced here differs from trees based on morphology and allozymes in three ways: M. sinica and M. radiata sit in two different branches of the tree; the two subspecies of M. assamensis are separated from one another; and M. arctoides consistently fell outside the rest of the sinica-group.(ABSTRACT TRUNCATED AT 250 WORDS)     

Multiple causation of phylogeographical pattern as revealed by nested clade analysis of the bamboo viper (Trimeresurus stejnegeri) within Taiwan

In order to assess the utility of nested clade analysis, both standard phylogenetic algorithms and nested clade analysis were performed on a geographically widespread survey of mitochondrial DNA haplotypes of the bamboo viper, Trimeresurus stejnegeri, within Taiwan. Gross tree topologies were congruent for all analyses and indicated the presence of two geographically overlapping clades within Taiwan. The smaller lineage was restricted to the north and east coasts, whereas the larger lineage occupied all but the northern range of the species within Taiwan including the Pacific offshore populations of Green and Orchid Islands. The phylogeographical pattern supports the existence of at least one colonization event from the continent since the initial isolation of Taiwan from the mainland in the Pliocene. However, determining the exact number of colonization events was not possible due to the simultaneous vicariant forces of hypothesized continental landbridge connections and the occurrence of dramatic in situ orogenesis throughout the Pleistocene. Nested clade analysis provided multiple temporal and spatial population historical inferences that are not possible with standard analyses and therefore should become widely applied to future phylogeographical studies.     

Extensive hybridization in hawksbill turtles (Eretmochelys imbricata) nesting in Brazil revealed by mtDNA analyses

Bahia state hosts over 90% of hawksbill (Eretmochelys imbricata) nests registered in the main nesting sites monitored by Projeto Tamar-IBAMA in Brazil. The genetic diversity of this hawksbill population (n=119) was assayed through the analyses of 752 bp of the mitochondrial DNA control region in nesting females. Seven distinct haplotypes, defined by 125 polymorphic sites, were found. Most of the individuals (n=67) display four typical hawksbill haplotypes, 50 individuals display two haplotypes characteristic of the loggerhead turtle (Caretta caretta) and two individuals had a haplotype affiliated with the olive ridley (Lepidochelys olivacea). These results demonstrate hybridization between the hawksbills and two species that nest along the Bahia coast. Of special interest is the high occurrence of loggerhead × hawksbill hybrids (42%), which display loggerhead mtDNA haplotypes but are characterized morphologically as hawksbills. The true hawksbill haplotypes present only three variable sites and low genetic diversity values (h=0.358±0.069; π=0.0005±0.0001). The occurrence of several nesting individuals with identical mtDNA from another species may also suggest a long history of introgression between species producing likely F2 or further generation hybrids. Marine turtle hybrids have been previously reported, but the high frequency observed in Bahia is unprecedented. Such introgression may influence evolutionary pathways for all three species, or may introduce novel morphotypes that develop apart from the parental species. The presence of a unique hybrid swarm has profound conservation implications and will significantly influence the development and implementation of appropriate management strategies for these species.     

Systematic relationships of Oriental tiny frogs of the family Microhylidae (Amphibia, Anura) as revealed by mtDNA genealogy

We estimated the genealogical relationships and assessed systematic relationships among 45 out of 89 named species and four unnamed taxa from 11 of 14 genera of the Oriental microhylids from 1767 bp sequences of the mitochondrial DNA genes 12S rRNA and 16S rRNA using maximum parsimony, maximum likelihood, and Bayesian inference methods. Monophyly was rejected for the subfamily Microhylinae, and our data reveal four well-supported clades whose relationships to each other are unresolved: (A) Microhyla, Calluella, and Glyphoglossus, (B) Chaperina, (C) Kaloula, Phrynella, and Metaphrynella, and (D) Micryletta. They were genetically as divergent from each other as from another Oriental subfamily Kalophryninae, and could be recognized as distinct subfamilies. Within Clade A, our data reveal three well-supported subclades whose relationships to each other are unresolved: (AI) Microhyla-I, (AII) Calluella and Glyphoglossus, and (AIII) Microhyla-II. Of the two enigmatic Malaysian genera, whose subfamilial placement has been undetermined, Phrynella was found to be the sister species of Metaphrynella in Clade C, whereas Gastrophrynoides was grouped in the Papua-Australian subfamily Asterophryinae. Currently recognized subgenera and species groups within Microhyla based on morphology were not supported phylogenetically, and require thorough reassessments.     

Analysis of 31 STR loci in the genetic isolate of Carloforte (Sardinia, Italy)

The genotypes of 31 autosomal short tandem repeat loci in the population of Carloforte were analyzed, these representing a linguistic and genetic isolate located on the island of Sardinia (Italy). The markers span the entire length of chromosomes 19, 20, 21 and 22. Allele frequencies and statistical parameters were presented for all loci. Observed heterozygosity ranged from 0.279 to 0.884, and polymorphism information content from 0.552 to 0.886. All but two loci showed Hardy-Weinberg equilibrium after Bonferroni correction. The 31 short tandem repeat loci examined in the present work provide additional data on the genetic structure of the Carloforte population.     

Genetic diversity and geographic differentiation in endangered Ammopiptanthus (Leguminosae) populations in desert regions of northwest China as revealed by ISSR analysis

• Background and Aims The desert legume genus Ammopiptanthuscomprises two currently endangered species, A. mongolicus andA. nanus. Genetic variability and genetic differentiation betweenthe two species and within each species were examined. • Methods Inter-simple sequence repeat (ISSR) marker datawere obtained and analysed with respect to genetic diversity,structure and gene flow. • Key Results Despite the morphological similarity betweenA. mongolicus and A. nanus, the two species are geneticallydistinct from each other, indicated by 63 % species-specificbands. Low genetic variability was detected for both populationlevel (Shannon indices of diversity H_pop = 0·106, percentageof polymorphic loci P = 18·55 % for A. mongolicus; H_pop= 0·070, P = 12·24 % for A. nanus) and specieslevel (H_sp = 0·1832, P = 39·39 % for A. mongolicus;H_sp = 0·1026, P = 25·89 % for A. nanus). Moderategenetic differentiation was found based on different measures(AMOVA _ST and Hickory ^B) in both A. mongolicus (0·3743–0·3744)and A. nanus (0·2162–0·2369). • Conclusions The significant genetic difference betweenthe two species might be due to a possible vicariant evolutionaryevent from a single common ancestor through the fragmentationof their common ancestor's range. Conservation strategies forthese two endangered species are proposed.     

Phylogeography and colonization history of Lesser Black‐backed Gulls (Larus fuscus) as revealed by mtDNA sequences

Abstract Because of the differential amplitude of climatic oscillations, species living at northern latitudes are subject to more frequent and more severe range oscillations than species at southern latitudes. As a consequence, northern populations should, on average, be phylogenetically younger and possess less phylogeographical structure than closely related taxa further south. To test these predictions, we studied the mitochondrial‐genetic population structure of NW Palearctic Lesser Black‐backed Gulls (Larus fuscus group [=LBBG], five taxa) breeding at temperate to boreal latitudes from Iceland to the Taimyr Peninsula. Results were compared with those previously obtained (Liebers et al. 2001. Mol. Ecol. 10 : 2447) for more southerly breeding Yellow‐legged Gulls (Larus cachinnans group, six taxa from the Atlantic Islands to Mongolia). Sequences of the hypervariable region I (HVR‐I) of the mitochondrial control region revealed low within‐ and between‐taxon sequence divergence, little genetic variation, a shallow haplotype phylogeny and poor phylogeographical structure in LBBGs compared with Yellow‐legged Gulls. Haplotype frequencies among the five northern taxa formed a stepped cline with significant gene flow restriction between the forms heuglini and fuscus, probably indicating a secondary contact with (partial?) reproductive isolation. Western forms of LBBG, among which mitochondrial gene flow appears unrestricted, show genetic signs of postglacial range expansion and population growth. The Larus fuscus group is derived from a cachinnans‐like ancestral population, probably in the Aralo‐Caspian basin, and spread from east (NW Siberia) to west within the Palearctic.     

Confocal analysis of cytoskeletal organisation within isolated chondrocyte sub-populations cultured in agarose

This study reports the cytoskeletal organisation within chondrocytes, isolated from the superficial and deep zones of articular cartilage and seeded into agarose constructs. At day 0, marked organisation of actin microfilaments was not observed in cells from both zones. Partial or clearly organised microtubules and vimentin intermediate filaments cytoskeletal components were present, however, in a proportion of cells. Staining for microtubules and vimentin intermediate filaments was less marked after 1 day in culture however than on initial seeding. For all three cytoskeletal components there was a dramatic increase in organisation between days 3 and 14 and, in general, organisation was greater within deep zone cells. Clear organisation for actin microfilaments was characterised by a cortical network and punctate staining around the periphery of the cell, while microtubules and vimentin intermediate filaments formed an extensive fibrous network. Cytoskeletal organisation within chondrocytes in agarose appears, therefore, to be broadly similar to that described in situ. Variations in the organisation of actin microfilaments between chondrocytes cultured in agarose and in monolayer are consistent with a role in phenotypic modulation. Vimentin intermediate filaments and microtubules form a link between the plasma membrane and the nucleus and may play a role in the mechanotransduction process.