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PubMed1987

Molecular analysis of a polymorphic domain of alpha satellite from the human X chromosome.

Alpha satellite DNA, a diverse family of tandemly repeated DNA sequences located at the centromeric region of each human chromosome, is organized in a highly chromosome-specific manner and is characterized by a high frequency of restriction-fragment-length polymorphism. To examine events underlying the formation and spread of these polymorphisms within a tandem array, we have cloned and sequenced a representative copy of a polymorphic array from the X chromosome and compared this polymorphic copy with the predominant higher-order repeat form of X-linked alpha satellite. Sequence data indicate that the polymorphism arose by a single base mutation that created a new restriction site (for HindIII) in the sequence of the predominant repeat unit. This variant repeat unit, marked by the new HindIII site, was subsequently amplified in copy number to create a polymorphic domain consisting of approximately 500 copies of the variant repeat unit within the X-linked array of alpha satellite. We propose that a series of intrachromosomal recombination events between misaligned tandem arrays, involving multiple rounds of either unequal crossing-over or sequence conversion, facilitated the spread and fixation of this variant HindIII repeat unit.

Chromosome Mapping↗

PubMed1988

Independent variations of myc amplification, inducibility, maturation, and proliferation states in HL60.

We have investigated the possible relationship between c-myc gene activity and other variable traits in HL60. In a panel of variant lines, a good correlation was observed between myc gene copy number and the level of myc mRNA. There was no correlation between myc amplification or expression and the resistance of the lines to induction of terminal neutrophilic or monocytic differentiation. Therefore, myc mRNA level does not appear to determine the ability of the variant HL60 lines to respond to inducers of differentiation. Flow cytometric analyses of the expression of a differentiation antigen (AGF 4.36) revealed stable negative and positive subpopulations in growing HL60. myc amplification, expression, and inducibility were identical in these subpopulations, suggesting that variation of these traits in HL60 sublines and variants is not due to maturation state differences. myc gene copy number was also identical in transferrin receptor positive (proliferating) and negative (resting) populations. These data contradict the notion that myc amplification has been important in determining the in vitro biological properties of HL60.

Cell Division↗

PubMed1998

Study of the frequencies of CYP1A1 gene polymorphisms and glutathione S-transferase mu1 gene in primary breast cancers: an update with an additional 114 cases.

We studied the polymorphisms m1 (Msp1 restriction site) and m2 (codon Val substitution) of CYP1A1 gene and the copy number of glutathione S-transferase mu1 (GSTM1) gene on 487 DNA of breast cancer primary tumours from Caucasian group. Tumours of patients aged 55 years and under at diagnosis presented a great proportion of wild m1 (-/-) genotype; 83.6% vs. 69.5% (p < 0.0006), and a higher percentage of copy number of GSTM1 equal or under one copy; 65.2% vs. 53.4% (p < 0.011) for older patients m1 and m2 variants are closely linked (p < 0.0000). Tumour with a low copy number of GSTM1 is correlated with high histological grading (p < 0.01) and high Cathepsin D concentrations (p < 0.02). The combinations of different genotypes showed that association wild m1 (-/-) genotype and copy number of GSTM1 inferior or equal to one copy is correlated with an early onset of breast cancer primary tumour 44% vs. 6.4% for m1 (-/+) or (+/+) genotype and copy number of GSTM1 superior to one (p < 0.0000). The CYP1A1 gene wild form seems to be associated with early cancer development in Caucasian patients.

Adult↗

PubMed1998

Expression of a Bacillus thuringiensis delta-endotoxin gene by Bacillus pumilus.

The delta-endotoxin genes from Bacillus thuringiensis were introduced into a rhizosphere-inhabiting Bacillus pumilus isolate to create a delta-endotoxin expression and delivery system for subterranean feeding insects such as the larvae of pale western cutworm (Agrotis orthogonia Morrison (Lepidoptera: Noctuidae)). Preliminary experiments indicated that Bacillus thuringiensis subsp. kurstaki cultures were toxic to pale western cutworm larvae. Three different cry genes from Bacillus thuringiensis subsp. kurstaki were cloned into high and low copy number vectors and mated into Bacillus pumilus RB8. When carried on high copy number vectors, cry genes appeared to inhibit sporulation and delta-endotoxin production in Bacillus pumilus RB8 cultures, since microscopic examination of these cultures revealed that < 0.1% of the cells of late stationary phase cultures had sporulated and produced parasporal inclusions. On low copy number vectors, the cry genes did not inhibit sporulation; however, production of delta-endotoxins was undetectable. Using a heat shock regime for enrichment of sporogenous crystalliferous variants, a Bacillus pumilus isolate, carrying cryIA(c) on a high copy number plasmid, was obtained in which high level delta-endotoxin production occurred concomitant with sporulation. Synthesis of functional delta-endotoxin by this strain was confirmed by Western blot analysis and bioassay with pale western cutworm larvae. These results show that rhizosphere-inhabiting bacilli are indeed a potential route for introduction of delta-endotoxins to the root environment for biocontrol purposes.

Animals↗

PubMed2026

Functions of tandem-repeat galectins and domain coordination governs galectin-4 activity in grass carp (Ctenopharyngodon idella).

Galectins are β-galactoside-binding lectins that play essential roles in innate immunity. Among them, tandem-repeat galectins (TrGals), typically composed of two distinct carbohydrate-recognition domains (CRDs) connected by a linker peptide, are well established as key regulators of pathogen recognition and host defense in mammals. However, their structural diversity and immunological functions in teleost fish remain poorly understood. In this study, five TrGals (Gal-4, Gal-8a, Gal-8b, Gal-9, and Gal-9like) were identified in grass carp. Sequence and structural analysis revealed that Gal-8a/b, Gal-9, and Gal-9like possess the canonical two-CRD architecture, whereas Gal-4 uniquely contains four highly similar tandem-repeat domains. All five TrGals were broadly expressed across examined tissues, with predominant expression in the liver. Upon Aeromonas hydrophila infection, Gal-4, Gal-8a, Gal-8b, and Gal-9 were rapidly up-regulated at early time points (3-6 h). To elucidate the functional significance of CRD number, recombinant full-length CiGal-4 (CiGal4-full) and three truncated variants containing one, two, or three CRDs (CiGal4-1CRD, CiGal4-2CRD, and CiGal4-3CRD) were generated and systematically characterized. All recombinant proteins contained the conserved β-sheet structure typical of galectin CRDs. Functional assays revealed that CiGal4-full displayed the strongest growth-inhibitory activity against all tested bacteria, whereas CiGal4-1CRD showed the weakest effect. Notably, CiGal4-2CRD exhibited the most potent bactericidal activity, surpassing the full-length protein, while CiGal4-3CRD showed no further enhancement. CiGal4-full and CiGal4-2CRD showed superior carbohydrate-binding activities compared with the other variants. Collectively, these results reveal that CRD copy number alone does not linearly determine galectin function. Instead, domain organization and conformational coordination are critical for optimizing antimicrobial activity. This study provides new insights into the structure-function relationships and evolutionary diversification of galectins in teleosts and highlights their potential as novel antimicrobial and immunomodulatory agents in aquaculture.

Animals↗

PubMed1996

Glycosyl-phosphatidylinositols of Trypanosoma congolense: two common precursors but a new protein-anchor.

The parasitic protozoan Trypanosoma congolense exhibits a dense surface coat which is pivotal for immunoevasion of the parasite. This dense surface coat is made of a single protein species, the variant surface glycoprotein, which is present in a high copy number. The protein is anchored to the plasma membrane by a glycosyl-phosphatidylinositol membrane anchor. A detailed study of the structure of T. congolense strain 423 (clone BENat 1.3) variant surface glycoprotein glycosyl-phosphatidylinositol membrane anchor was performed. Radioactively labelled core-glycan prepared by dephosphorylation, deamination and reduction was analysed by high-pH anion-exchange chromatography, size-exclusion and lectin affinity chromatography. Additionally the glycosyl-phosphatidylinositol membrane anchor core-glycan was purified from a bulk preparation of variant surface glycoprotein and subjected to mass spectrometry and methylation analysis. Using these methods we could identify a novel galactose-beta 1,6-N-acetyl-glucosamine-beta 1,4-branch modifying the mannose adjacent to the glucosamine of the mannose-alpha 1,2-mannose-alpha 1,6-mannose-alpha 1,4-glucosamine core-glycan of the variant surface glycoprotein glycosyl-phosphatidylinositol membrane anchor. Furthermore the biosynthetic pathway leading to this novel structure was investigated. Two putative glycosyl-phosphatidylinositol anchor precursors were identified having structures identical to the previously characterized Trypanosoma brucei brucei glycolipids P2 and P3 (also designated glycolipid A and C) consistent with a trimannosyl core and a dimyristoyl-glycerol. Both glycosyl-phosphatidylinositol anchor precursors of T. congolense do not possess the side-branch modification found on the mature protein membrane anchor, implying that the sugar side-chain is added to the anchor during its passage through the Golgi-apparatus.

Animals↗

PubMed1999

Expression and cellular localization of ribonucleotide reductase small subunit M2 protein in hydroxyurea-resistant Leishmania mexicana amazonensis.

We raised a specific antiserum against the recombinant M2 subunit protein of ribonucleotide reductase of Leishmania mexicana amazonensis in rabbit. This antiserum was used to study the expression and cellular location of the M2 protein in wildtype as well as hydroxyurea-resistant variants (HuR) of the parasite. The protein increased with increasing dose of the drug used for selection of resistance. The increase in protein level was accompanied by an increase in the copy numbers of mRNA of the M2 gene in the variants. In contrast to mammalian cells, the M2 protein of Leishmania is located in the nucleus rather than in the cytoplasm. The number of cells expressing M2 protein is also different in mammalian cells versus Leishmania. In mammalian cells, expression of M2 protein is a strictly S-phase-correlated event and in exponentially growing cells only approximately 50% of the cells are in S-phase and only these cells synthesize M2 protein. In L. m. amazonensis, however, almost all exponentially growing cells are positive for M2 protein. This makes it unlikely that M2 protein expression in Leishmania is S-phase dependent. In view of these findings, a fresh look in the future into the regulatory mechanisms of synthesis and the site of action of RNR in L. m. amazonensis is warranted.

Animals↗

PubMed1996

Cloning of heterologous genes specifying detrimental proteins on pUC-derived plasmids in Escherichia coli.

A system is described that enables the cloning of genes specifying detrimental proteins in Escherichia coli. The system is based on pUC plasmids and was developed for the expression of the Bacillus subtilis csaA gene, which is lethal when expressed at high levels. Suppressor strains that tolerate the presence of plasmids for high-level expression of csaA were isolated, which contained small cryptic deletion variants of the parental plasmid in high copy numbers. The cryptic plasmids consisted mainly of the pUC replication functions and lacked the csaA region and selectable markers. The co-resident, incompatible, cryptic plasmids enabled the maintenance of the csaA plasmids by reducing their copy number 20-fold, which resulted in a concomitant 3- to 7-fold reduction in the expression of plasmid-encoded genes. Strains carrying these cryptic endogenous plasmids proved to be useful for the construction of pUC-based recombinant plasmids carrying other genes, such as the skc gene of Streptococcus equisimilis, which cannot be cloned in high copy numbers in E. coli. Several strategies to reduce production levels of heterologous proteins specified by plasmids are compared.

Bacterial Outer Membrane Proteins↗

PubMed1999

Amplification of a pseudogene cassette underlies euchromatic variation of 16p at the cytogenetic level.

Euchromatic imbalances at the cytogenetic level are usually associated with phenotypic consequences. Among the exceptions are euchromatic variants of chromosomes 8, 9, 15 and 16, which have each been reported in multiple unrelated families. In this paper, we present a new family and an unrelated individual who have euchromatic variants of 16p. Enhanced hybridisation to the extra material was found by using fluorescence in situ hybridisation with cosmids for both the 16p11.2-specific non-functional immunoglobin heavy chain segments and the pseudogenetic 16p11.2 creatine transporter region. Computerised measurement of the fluorescent signals was consistent with amplification of a pseudogene cassette comprising both these paralogous domains, which were originally transposed from 14q32.3 and Xq28, respectively. Amplification of pseudogenetic sequences is consistent with the normal phenotype in 36/46 carriers from the 18 families reported to date. Inconsistent phenotypic anomalies in the remaining 10 carriers probably reflect bias of ascertainment. These results are analogous to the amplification of the 15q11.2-specific pseudogene cassette in euchromatic variants of chromosome 15. They also suggest that the majority of established euchromatic variants are associated with variation in the copy number of sequences that have been dispersed between pericentromeric and telomeric loci over recent evolutionary time. We propose that constitutional cytogenetic amplification of this kind is part of a more widespread continuum of genomic flux affecting regions in which heterochromatin and euchromatin interpose. Euchromatic sequences that vary in a heterochromatic manner might usefully be termed "hemichromatic".

Adolescent↗

PubMed2026

The role of circulating tumor DNA (ctDNA) to detect minimal residual disease in locally advanced gastroesophageal carcinoma: the BUTTERFLY study.

BACKGROUND: Despite advances in perioperative and neoadjuvant strategies, patients with locally advanced gastroesophageal cancers remain at high risk of recurrence after curative intent treatment. No validated biomarkers are available to detect minimal residual disease (MRD) or to guide post-operative risk-adapted management. Circulating tumor DNA (ctDNA) has emerged as a noninvasive tool for disease monitoring; single-parameter or tumor-informed assays, however, may lack sensitivity in low-tumor burden settings. Multimodal, tumor-agnostic approaches may overcome these limitations. METHODS: The BUTTERFLY study is a prospective, multicenter observational study enrolling patients with stage II-III gastric, gastroesophageal junction, or esophageal cancer treated with perioperative chemotherapy or neoadjuvant chemoradiotherapy followed by surgery. It evaluates the diagnostic performance and prognostic value of an academic, tumor-agnostic, multimodal ctDNA assay for MRD detection and prognostic stratification. Serial plasma samples are collected from baseline through post-operative follow-up and at relapse. Cell-free DNA is analyzed using the Agnostic Liquid Biopsy Multimodal Advancement (ALMA) platform, integrating tumor fraction estimation, somatic copy number alterations, fragmentomic features, single-nucleotide variants, and whole-genome methylation profiling. Multimodal features are combined with clinical variables using machine learning-based models to enhance MRD detection and relapse risk stratification. The primary endpoint includes sensitivity and specificity of ALMA-defined ctDNA/MRD status at the 4-8 weeks after surgery landmark, whereas secondary endpoints assess diagnostic performance at other time points and associations between ctDNA status and dynamics with disease-free survival, overall survival, treatment response, and lead time to recurrence. FUTURE PERSPECTIVES: If validated, this tumor-agnostic, multimodal ctDNA approach may enable earlier molecular relapse detection and support personalized post-operative management strategies.

circulating tumor DNA (ctDNA)↗

PubMed2026

Eribulin versus taxane as first-line chemotherapy combined with dual HER2 blockade in patients with HER2-positive locally advanced or metastatic breast cancer: final survival outcomes of the JBCRG-M06/EMERALD study.

BACKGROUND: The phase III JBCRG-M06/EMERALD study was the first to show noninferior progression-free survival (PFS) of eribulin to taxane, combined with dual human epidermal growth factor receptor 2 (HER2) blockade (trastuzumab plus pertuzumab), as a first-line treatment for HER2-positive locally advanced breast cancer or metastatic breast cancer (LABC/MBC). We report final survival outcomes and biomarker analyses of the EMERALD trial. PATIENTS AND METHODS: Patients with HER2-positive LABC/MBC were randomly assigned 1:1 to either eribulin or physician-choice taxane (docetaxel or paclitaxel), both combined with trastuzumab plus pertuzumab, as first-line chemotherapy. PFS and overall survival (OS) were assessed through 30 June 2023 for PFS and 31 December 2024 for OS. Survival outcomes were compared between the eribulin and taxane groups and according to circulating tumor DNA (ctDNA) detection of PIK3CA mutations (PIK3CAm+; E542K, E545K, H1047R, and N345K single nucleotide variants) or HER2 amplification (HER2 amp+; ERBB2 copy number >2.5). RESULTS: Median OS was 78.5 months [95% confidence interval (CI) 64.3-not reached (NR)] for eribulin and was NR for taxane, with a hazard ratio of 1.25 (95% CI 0.92-1.71, log-rank P = 0.19). The 60-month OS rates were 59.7% and 65.2% for eribulin and taxane, respectively. Median OS and 60-month OS rates were numerically lower in ctDNA PIK3CAm+ patients, and greater in ctDNA HER2 amp+ patients for all patients and with stratification by treatment group. There were no statistical interactions between treatment group with either ctDNA PIK3CAm or ctDNA HER2 amp status. Similar patterns were observed for PFS. CONCLUSION: Final survival analysis revealed that median OS exceeded 6 years with eribulin or physician-choice taxane, combined with trastuzumab plus pertuzumab, as first-line chemotherapy for HER2-positive LABC/MBC, with no significant differences between the two groups. ctDNA PIK3CAm+ status was a poor prognostic factor. ctDNA HER2 amp+ was associated with longer survival.

Aged↗

PubMed2026

Integrated signatures define mutational processes in prostate cancer.

Prostate cancer follows a long and heterogeneous disease course with incompletely understood aetiology1. Here we dissect the mutational processes shaping the genomes of 959 donors from the Pan Prostate Cancer Group and assess their clinical relevance. By integrating de novo extracted single-base substitution, insertion-deletion and copy-number signatures with six novel complex structural variant signatures, we identify eight integrated mutational footprints (IMFs) that collectively explain the mutational processes in 85% of primary prostate cancer genomes. IMFs were strongly influenced by regional biases in the genome, most prevalently androgen receptor-mediated mutagenesis and replication stress. Four IMFs, present in 37% of primary tumours, were significantly associated with shorter time to metastasis. These included reactive oxygen-species-driven mutagenesis and both canonical and non-canonical homologous recombination deficiency, the latter being enriched in patients of African ancestry. Extending to the metastatic setting, we found that IMFs predicted sensitivity to androgen receptor pathway inhibitors. Taken together, our study delineates the aetiologies and mutational processes that drive the genomic and clinical heterogeneity of prostate cancer, introduces IMFs as a unifying framework, and highlights their potential to improve both risk stratification and biomarker-guided treatment selection.

Journal Article↗

PubMed1997

Evolutionary dynamics of tandem repeats in the mitochondrial DNA control region of the minnow Cyprinella spiloptera.

Length variation due to tandem repeats is now recognized as a common feature of animal mitochondrial DNA; however, the evolutionary dynamics of repeated sequences are not well understood. Using phylogenetic analysis, predictions of three models of repeat evolution were tested for arrays of 260-bp repeats in the cyprinid fish Cyprinella spiloptera. Variation at different nucleotide positions in individual repeats supported different models of repeat evolution. One set of characters included several nucleotide variants found in all copies from a limited number of individuals, while the other set included an 8-bp deletion found in a limited number of copies in all individuals. The deletion and an associated nucleotide change appear to be the result of a deterministic, rather than stochastic, mutation process. Parallel origins of repeat arrays in different mitochondrial lineages, possibly coupled with a homogenization mechanism, best explain the distribution of nucleotide variation.

Animals↗

PubMed2005

Mapping segmental and sequence variations among laboratory mice using BAC array CGH.

We used arrays of 2069 BACs (1303 nonredundant autosomal clones) to map sequence variation among Mus spretus (SPRET/Ei and SPRET/Glasgow) and Mus musculus (C3H/HeJ, BALB/cJ, 129/J, DBA/2J, NIH, FVB/N, and C57BL/6) strains. We identified 80 clones representing 74 autosomal loci of copy number variation (|log(2)ratio| >/= 0.4). These variant loci distinguish laboratory strains. By FISH mapping, we determined that 63 BACs mapped to a single site on C57BL/6J chromosomes, while 17 clones mapped to multiple chromosomes (n = 16) or multiple sites on one chromosome (n = 1). We also show that small ratio changes (Delta log(2)ratio approximately 0.1) distinguish homozygous and heterozygous regions of the genome in interspecific backcross mice, providing an efficient method for genotyping progeny of backcrosses.

Animals↗

PubMed2025

Deep clinical and genetic analysis of 17p13.3 region: 38 pediatric patients diagnosed using next-generation sequencing and literature review.

BACKGROUND: Chromosome 17p13.3 is a region of genomic instability associated with different neurodevelopmental diseases. The malformation spectrum of 17p13.3 microdeletions ranges from an isolated lissencephaly sequence to Miller-Dieker syndrome, while 17p13.3 microduplications result in autism, learning disabilities, microcephaly and other brain malformations. This study aims to provide a more comprehensive delineation of the clinical and genetic characteristics associated with 17p13.3 alterations. METHODS: We retrospectively analyzed the next-generation sequencing (NGS) data of more than 40 thousand patients from January 2016 to December 2021 and identified 38 pediatric patients with copy-number variations (CNVs) or single-nucleotide variations (SNVs) in 17p13.3 region. Published patients with CNVs in the 17p13.3 region were also collected and we performed a Chi-square test to compare the phenotype spectrum of microdeletions and microduplications. RESULTS: Among the 27 CNV patients, 20 patients with microdeletions and 7 patients with microduplications were found. PAFAH1B1 was the most frequently deleted gene and CRK was the most frequently duplicated gene. Affected genes in 11 SNV patients included PAFAH1B1 and PRPF8. Developmental delay was the most common abnormality detected in the 38 patients (29/38, 76.3%). Of note, Case 10 presented omphalocele and Case 23 presented scoliosis, webbed neck and bone cyst, all of which were unusual variant phenotypes in this region. The Chi-square test revealed that epilepsy, lissencephaly and short stature were statistically significant with microdeletions, while behavioral abnormalities and hand and foot abnormalities were significant with microduplications (p < 0.01). CONCLUSIONS: While PAFAH1B1, YWHAE and CRK are associated with major phenotypes of 17p13.3, RTN4RL1 may be involved in white matter changes and HIC1 might contribute to the occurrence of omphalocele. This study provided a comprehensive understanding of genetic information and phenotype spectrum of the 17p13.3 region.

Humans↗

PubMed2005

Copy number polymorphism and expression level variation of the human alpha-defensin genes DEFA1 and DEFA3.

We have defined unexpectedly extensive copy number variation at the human anti-microbial alpha-defensin genes DEFA1 and DEFA3, encoding human neutrophil peptides HNP-1, HNP-2 and HNP-3. There was variation in both number and position of DEFA1/DEFA3 genes in arrays of 19 kb tandem repeats on 8p23.1, so that the DEFA1 and DEFA3 genes appear to be interchangeable variant cassettes within tandem gene arrays. For this reason, the official symbol for this locus has been revised to DEFA1A3. The total number of gene copies per diploid genome varied between four and 11 in a sample of 111 control individuals from the UK, with approximately 10% (11/111) of people lacking DEFA3 completely. DEFA1 appeared to be at high copy number in all great apes studied; at one variable site in the repeat unit, both variants have persisted in humans, chimpanzees and gorillas since their divergence. Analysis of expression levels in human white blood cells showed a clear correlation between the relative proportions of DEFA1:DEFA3 mRNA and corresponding gene numbers. However, there was no relationship between total (DEFA1+DEFA3) mRNA levels and total gene copy number, suggesting the superimposed influence of trans-acting factors. The persistence of DEFA1 at high copy number in other apes suggests an alternative model for the early stages of the evolution of novel genes by duplication and divergence. Duplicated genes present in variant tandem arrays may have greater potential than simple duplications for the combinatorial creation of new functions by recombination and gene conversion, while still preserving pre-existing functions on the same haplotype.

Blotting, Southern↗

PubMed2003

Genomic localization of endogenous mobile CACTA family transposons in natural variants of Arabidopsis thaliana.

The differentiation between gene-rich and transposon-rich (gene-poor) regions is a common feature of plant genomes. This may be due to preferential integration of transposons into gene-poor regions or may be due to purifying selection against transposon insertion into gene-rich regions. We examined the distribution of a low-copy-number mobile subfamily of Arabidopsis CACTA transposons in the genomes of 19 natural variants (ecotypes) of A. thaliana, and compared that to the pattern of integrations induced in the laboratory by mutation of the DDM1 (Decrease in DNA Methylation) gene. Sequences similar to mobile CACTA1 copies were distributed among the ecotypes and showed high degrees of polymorphism in genomic localization. Despite the high level of polymorphism, the copy number was low in all the ecotypes examined, and the elements were localized preferentially in pericentromeric and transposon-rich regions. This contrasts with the pattern of transposition induced by the ddm1 mutation, in which the range of integration sites is less biased and the copy number frequently increases. Based on these observations, we discuss the possible contribution of natural selection and chromatin structure to the distribution of transposons.

Arabidopsis↗

PubMed1994

Mitochondrial DNA diversity in the pea aphid Acyrthosiphon pisum.

The pea aphid Acyrthosiphon pisum has been established in North America for at least a century and occurs on a broad range of host plants. Despite its importance as a crop pest, there is little understanding of the genetic structure of its populations or the extent of genetic divergence associated with different host plant utilization. This study examined the extent of mitochondrial DNA (mtDNA) diversity among 35 clones of pea aphids from alfalfa. Polymorphisms were detected at only 2 of 126 restriction sites, suggesting the same impoverished level of genetic diversity found in prior allozyme studies. However, length variation was common and apparently arose as a result of tandem repeats in two regions of the mtDNA molecule. Region 1 occurred in proximity to the control region of the molecule, while region 2 was close to a cluster of tRNA genes flanking the NAD-dehydrogenase subunit 3 gene on the opposite side of the mtDNA molecule. Each of the aphid clones was homoplasmic for a single length variant in region 1, which varied with respect to the number of copies of a 120-bp repeat. By contrast, one-third of the clones were heteroplasmic at region 2, where they possessed a variable number of copies of a 210-bp repeat. Reanalysis of clones after 30 generations of parthenogenetic reproduction established the stability of length variants over this interval, suggesting their value in studies of the genetic structure of aphid populations.

Animals↗