Density Of Microsatellites Research Articles

MicrosatNavigator: exploring nonrandom distribution and lineage-specificity of microsatellite repeat motifs on vertebrate sex chromosomes across 186 whole genomes.

Microsatellites are short tandem DNA repeats, ubiquitous in genomes. They are believed to be under selection pressure, considering their high distribution and abundance beyond chance or random accumulation. However, limited analysis of microsatellites in single taxonomic groups makes it challenging to understand their evolutionary significance across taxonomic boundaries. Despite abundant genomic information, microsatellites have been studied in limited contexts and within a few species, warranting an unbiased examination of their genome-wide distribution in distinct versus closely related-clades. Large-scale comparisons have revealed relevant trends, especially in vertebrates. Here, "MicrosatNavigator", a new tool that allows quick and reliable investigation of perfect microsatellites in DNA sequences, was developed. This tool can identify microsatellites across the entire genome sequences. Using this tool, microsatellite repeat motifs were identified in the genome sequences of 186 vertebrates. A significant positive correlation was noted between the abundance, density, length, and GC bias of microsatellites and specific lineages. The (AC)n motif is the most prevalent in vertebrate genomes, showing distinct patterns in closely related species. Longer microsatellites were observed on sex chromosomes in birds and mammals but not on autosomes. Microsatellites on sex chromosomes of non-fish vertebrates have the lowest GC content, whereas high-GC microsatellites (≥ 50M% GC) are preferred in bony and cartilaginous fishes. Thus, similar selective forces and mutational processes may constrain GC-rich microsatellites to different clades. These findings should facilitate investigations into the roles of microsatellites in sex chromosome differentiation and provide candidate microsatellites for functional analysis across the vertebrate evolutionary spectrum.

Comparative analysis of nine Tilletia indica genomes for the development of novel microsatellite markers for genetic diversity and population structure analysis.

Karnal bunt (KB; Tilletia indica) is the prime quarantine concern for quality wheat production throughout the world. The most effective approach to dealing with this biotic stress is to breed KB-resistant wheat varieties, which warrants a better understanding of T. indica genome architecture. In India, the North Western Plain Zone is the prime hot spot for KB disease, but only limited efforts have been made to decipher T. indica diversity at the genomic level. Microsatellites offer a powerful and robust typing system for the characterization and genetic diversity assessment of plant pathogens. At present, inadequate information is available with respect to the development of genome-derived markers for revealing genetic variability in T. indica populations. In current research, nine complete genome sequences of T. indica (PSWKBGH_1, PSWKBGH_2, PSWKBGD_1_3, RAKB_UP_1, TiK_1, Tik, DAOMC236408, DAOMC236414, and DAOMC236416) that exist in the public domain were explored to know the dynamic distribution of microsatellites. Comparative genome analysis revealed a high level of relative abundance and relative density of microsatellites in the PSWKBGH_1 genome in contrast to other genomes. No significant correlation between microsatellite distribution for GC content and genome size was established. All the genomes showed the dominance of tri-nucleotide motifs, followed by mono-, di-, tetra-, hexa-, and penta-nucleotide motifs. Out of 50 tested markers, 36 showed successful amplification in T. indica isolates and produced 52 different alleles. A PCR assay along with analysis of the polymorphic information content (PIC) revealed 10 markers as neutral and polymorphic loci (PIC 0.37). The identified polymorphic SSR loci grouped a geographically distinct T. indica population of 50 isolates representing seven Indian regions (Jammu, Himachal Pradesh, Punjab, Haryana, Uttarakhand, Uttar Pradesh, and Rajasthan) into four distinct clusters. The results of the analysis of molecular variance identified 94% genetic variation within the population and 6% among the population. Structure analysis also confirmed the existence of four genetically diverse groups containing admixtures of T. indica isolates across populations. In nutshell, the current study was successful in identifying novel, neutral and polymorphic microsatellite markers that will be valuable in offering deep insight into the evolutionary relationship and dynamics of the T. indica population for devising effective KB management strategies in wheat.

Design and research of integrated components for microsatellite thermal control system

With the increasing development of aerospace technology, micro satellites have attracted high attention in the aerospace field due to their advantages such as short development cycle, low system investment, and flexible launch methods. Their high level of internal equipment integration, high heat flux density, complex and uncertain working modes pose new challenges to thermal control design. At present, the thermal control design of micro satellites still mainly adopts passive methods, while active thermal control design has been widely used in the fluid circuit of large spacecraft, mostly in the “task oriented design mode”. Its high design cost, long cycle, poor adaptability and other characteristics cannot be applied to low cost, short cycle, and flexible launch methods of micro satellites. In response to the new problems brought by the high power density and low thermal inertia of microsatellites in thermal control design, this paper proposes an active thermal control fluid loop system suitable for microsatellites. In addition to the cold plate and radiator at the equipment end, other equipment forms an integrated component in the form of a shared substrate. The integrated component has the characteristics of miniaturization, lightweight, and rapid replacement of board and card. Through simulation and technical analysis of key components, We believe that this scheme is reasonable and feasible, providing a new design scheme for the thermal control design of subsequent micro satellites.

Reevaluation of Parasynechococcus-like Strains and Genomic Analysis of Their Microsatellites and Compound Microsatellites.

Morphologically similar to Synechococcus, a large number of Parasynechococcus strains were misclassified, resulting in extreme underestimation of their genetic diversity. In this study, 80 Synechococcus-like strains were reevaluated using a combination of 16S rRNA phylogeny and genomic approach, identifying 54 strains as Parasynechococcus-like strains and showing considerably intragenus genetic divergence among the subclades identified. Further, bioinformatics analysis disclosed diversified patterns of distribution, abundance, density, and diversity of microsatellites (SSRs) and compound microsatellites (CSSRs) in genomes of these Parasynechococcus-like strains. Variations of SSRs and CSSRs were observed amongst phylotypes and subclades. Both SSRs and CSSRs were in particular unequally distributed among genomes. Dinucleotide SSRs were the most widespread, while the genomes showed two patterns in the second most abundant repeat type (mononucleotide or trinucleotide SSRs). Both SSRs and CSSRs were predominantly observed in coding regions. These two types of microsatellites showed positive correlation with genome size (p < 0.01) but negative correlation with GC content (p < 0.05). Additionally, the motif (A)n, (AG)n and (AGC)n was a major one in the corresponding category. Meanwhile, distinctive motifs of CSSRs were found in 39 genomes. This study characterizes SSRs and CSSRs in genomes of Parasynechococcus-like strains and will be useful as a prerequisite for future studies regarding their distribution, function, and evolution. Moreover, the identified SSRs may facilitate fast acclimation of Parasynechococcus-like strains to fluctuating environments and contribute to the extensive distribution of Parasynechococcus species in global marine environments.

A comparative study of microsatellites among crocodiles and development of genomic resources for the critically endangered Indian gharial.

Next-generation sequencing has allowed us to explore new methods, where comparative and population genomics can be used simultaneously. Keeping this in mind, we surveyed and analyzed the frequency and distribution of microsatellites in the Indian gharial (Gavialis gangeticus) and compared it with American alligator (Alligator mississippiensis) and saltwater crocodile (Crocodylus porosus) to enrich them with genomic resources. TheIndian gharial has a low frequency, relative abundance (RA), and relative density (RD) of microsatellites as compared to other crocodilians. RA and RD were positively correlated with the GC content of genomic and transcriptomic sequences. The genomic sequences were dominated by dinucleotide repeats, whereas the transcriptomic sequences had an excess of trinucleotide repeats. Motif conservation studies among the three crocodilians revealed conservation of 69.2% of motifs. Species-specific unique motifs identified in this study could be used as molecular probes for species identification. A total of 67,311 primers were designed in all three species to enrich the crocodilians with genomic resources. The genomic resources developed in this study could accelerate diversity analysis within its individuals to design a proper mating plan to reduce inbreeding stress and further improve the species.

A Comprehensive Plant microRNA Simple Sequence Repeat Marker Database to Accelerate Genetic Improvements in Crops

Microsatellites, or simple sequences repeat (SSRs), are distributed in genes, intergenic regions and transposable elements in the genome. SSRs were identified for developing markers from draft genome assemblies, transcriptome sequences and genome survey sequences in plant and animals. The identification, distribution, and density of microsatellites in pre-microRNAs (miRNAs) are not well documented in plants. In this study, SSRs were identified in 16,892 pre-miRNA sequences from 292 plant species in six taxonomic groups (algae to dicots). Fifty-one percent of pre-miRNA sequences contained SSRs. Mononucleotide repeats were the most abundant, followed by di- and trinucleotide repeats. Tetra-, penta-, and hexarepeats were rare. A total of 9,498 (57.46%) microsatellite loci had potential as pre-miRNA SSR markers. Of the markers, 3,573 (37.62%) were non-redundant, and 2,341 (65.51%) primer pairs could be transferred to at least one of the plant taxonomic groups. All data and primer pairs were deposited in a user-friendly, freely accessible plant miRNA SSR marker database. The data presented in this study, accelerate the understanding of pre-miRNA evolution and serve as valuable genomic treasure for genetic improvements in a wide range of crops, including legumes, cereals, and cruciferous crops.

Comparative Genome-Wide Characterization of Microsatellites in Candida albicans and Candida dubliniensis Leading to the Development of Species-Specific Marker

Background: Microsatellites or simple sequence repeats (SSR) are related to genomic structure, function, and certain diseases of taxonomically different organisms. Objective: To characterize microsatellites in two closely related Candida species by searching and comparing 1–6 bp nucleotide motifs and utilizing them to develop species-specific markers. Methods: Whole-genome sequence was downloaded from the public domain, microsatellites were mined and analyzed, and primers were synthesized. Results: A total of 15,821 and 7,868 microsatellites, with mono-nucleotides (8,679) and trinucleotides (3,156) as most frequent microsatellites, were mined in Candida dubliniensis and Candida albicans, respectively. Chromosome size was found positively correlated with microsatellite number in both the species, whereas it was negatively correlated with the relative abundance and density of microsatellites. A number of unique motifs were also found in both the species. Overall, microsatellite frequencies of each chromosome in C. dubliniensis were higher than in C. albicans. Conclusion: The features of microsatellite distribution in the two species’ genomes revealed that it is probably not conserved in the genus Candida. Data generated in this article could be used for comparative genome mapping and understanding the distribution of microsatellites and genome structure between these closely related and phenotypically misidentified species and may provide a foundation for the development of a new set of species-specific microsatellite markers. Here, we also report a novel microsatellite-based marker for C. dubliniensis-specific identification.

A comparative survey of microsatellites among wild and domestic cat provides valuable resources for marker development.

Information on the level and distribution of genetic variation is important for conservation plan of captive population of an endangered species such as tiger and cheetah. We assayed the frequency of microsatellites in the genomic and genic sequences of wild cats (Panthera tigris, Acinonyx jubatus) and compared it with the domestic cat (Felis catus). Frequency, relative abundance and density of microsatellites were highest in the domestic cat when compared with wild cats. The frequency of microsatellites was positively correlated with the G+C content of genomic and genic sequences. The maximum frequency of microsatellites among all three sequence sets was of di-nucleotide repeats (genomic-88.1%; genic-70.4%), whereas the hexa-nucleotide repeat represents < 0.5%. Motif conservation study among the genomic and genic sequences revealed conservation of 81.3% and 51.0% motif within the members of family Felidae. A total 40,233 primers from genic sequences were designed in order to enrich the members of family Felidae with genomic resources. The designed primers could be useful in determining the molecular genetics of population structure and individualization of a particular cat.

Imperfect and Compound Microsatellites in the Genomes of Burkholderia pseudomallei Strains

Evolution of microsatellites (or simple sequence repeats, SSRs) is a complex process that converts perfect repeats to novel structural elements with functions poorly understood, such as imperfect and compound microsatellites. An in silico analysis often Burkholderia pseudomallei genomes revealed 215683 micro-satellites, and more than 98% of them proved imperfect. The density of microsatellites in the genome ranged from 2922.7 to 3022.6 per Mbp. Approximately 10.20-10.67% of the repeats were parts of compound micro-satellites. The of compound microsatellite density varied from 144.7 to 150.6 per Mbp. Between-strain differences in microsatellite distribution were explained by a direct correlation of the SSR density with the GC content and an inverse relationship between the SSR density and the genome size. For each B. pseudomallei chromosome, the SSR density similarly correlated with its size and GC content. Chromosome 2 showed a significant correlation between the SSR and compound microsatellite densities (r = 0.93, p < 10^(-3)). The association of imperfect and compound microsatellite densities with the structural features of each chromosome and the fact that motifs are degenerate and occur in few copies in the majority of B. pseudomallei microsatellites agree with the previous hypothesis of negative selection affecting extended SSRs. The mechanism of selection possibly involves an accumulation of point mutations, which lead to an interruption of the repeat during replication because easily passable secondary structures may form to stabilize the microsatellite length.

A comparative genomics approach revealed evolutionary dynamics of microsatellite imperfection and conservation in genus Gossypium

BackgroundOngoing molecular processes in a cell could target microsatellites, a kind of repetitive DNA, owing to length variations and motif imperfection. Mutational mechanisms underlying such kind of genetic variations have been extensively investigated in diverse organisms. However, obscure impact of ploidization, an evolutionary process of genome content duplication prevails mostly in plants, on non-coding DNA is poorly understood.ResultsGenome sequences of diversely originated plant species were examined for genome-wide motif imperfection pattern, and various analytical tools were employed to canvass characteristic relationships among repeat density, imperfection and length of microsatellites. Moreover, comparative genomics approach aided in exploration of microsatellites conservation footprints in Gossypium evolution. Based on our results, motif imperfection in repeat length was found intricately related to genomic abundance of imperfect microsatellites among 13 genomes. Microsatellite decay estimation depicted slower decay of long motif repeats which led to predominant abundance of 5-nt repeat motif in Gossypium species. Short motif repeats exhibited rapid decay through the evolution of Gossypium lineage ensuing drastic decrease of 2-nt repeats, of which, “AT” motif type dilapidated in cultivated tetraploids of cotton.ConclusionThe outcome could be a directive to explore comparative evolutionary footprints of simple non-coding genetic elements i.e., repeat elements, through the evolution of genus-specific characteristics in cotton genomes.

A Comprehensive Characterization of Simple Sequence Repeats in the Sequenced Trichoderma Genomes Provides Valuable Resources for Marker Development.

Members of genus Trichoderma are known worldwide for mycoparasitism. To gain a better insight into the organization and evolution of their genomes, we used an in silico approach to compare the occurrence, relative abundance and density of SSRs in Trichoderma atroviride, T. harzianum, T. reesei, and T. virens. Our analysis revealed that in all the four genome sequences studied, the occurrence, relative abundance, and density of microsatellites varied and was not influenced by genome sizes. The relative abundance and density of SSRs positively correlated with the G + C content of their genomes. The maximum frequency of SSRs was observed in the smallest genome of T. reesei whereas it was least in second smallest genome of T. atroviride. Among different classes of repeats, the tri-nucleotide repeats were abundant in all the genomes and accounts for ∼38%, whereas hexa-nuceotide repeats were the least (∼10.2%). Further evaluation of the conservation of motifs in the transcript sequences shows a 49.5% conservation among all the motifs. In order to study polymorphism in Trichoderma isolates, 12 polymorphic SSR markers were developed. Of the 12 markers, 6 markers are from T. atroviride and remaining 6 belong to T. harzianum. SSR markers were found to be more polymorphic from T. atroviride with an average polymorphism information content value of 0.745 in comparison with T. harzianum (0.615). Twelve polymorphic markers obtained in this study clearly demonstrate the utility of newly developed SSR markers in establishing genetic relationships among different isolates of Trichoderma.

In silico genome-wide identification and analysis of microsatelliterepeats in the largest RNA virus family (Closteroviridae)

Microsatellites are known to exhibit ubiquitous presence across all kingdoms of life, including viruses. Members of the family Closteroviridae are the largest RNA viruses and severely affect different agricultural crops worldwide, including1397645907citrus, grapevine, and vegetables. Here we identified and systematically analyzed the nature and distribution of both simple and complex microsatellites present in the complete genome of 36 species belonging to Closteroviridae. Our results showed, in all analyzed genomes, that neither genome size nor GC content had any influence on number, relative abundance, or relative density of microsatellites. For each genome, dinucleotide repeats were found to be highly predominant and AT/TA and AG/GA were the two most abundant dinucleotide repeat motifs. Repeats larger than trinucleotide were relatively rare in these viral genomes. Comparative study of occurrence, abundance, and density of microsatellites among available RNA and DNA viral genomes indicated that simple repeats were less abundant in genomes of Closteroviridae. To our knowledge, this is the first analysis of microsatellites occurring in the largest viral genome that infects plants. Characterization of such variations in repeat sequences would be important in deciphering the origin, mutational processes, and role of repeat sequences in viral genomes.

Genome wide survey and analysis of microsatellites in Tombusviridae family

Microsatellites are small repetitive sequences found in all kingdoms of life including viruses. Members of the Tombusviridae family severely affect growth of wide range of plants and reduce economic yield in diverse cropping systems worldwide. Here, we analyzed the nature and distribution of both simple and complex microsatellites present in complete genome of 47 species of Tombusviridae family. Our results showed, in all analyzed genomes, genome size and GC content had a weak influence on number, relative abundance and relative density of microsatellites, respectively. For each genome, dinucleotide repeats followed by mononucleotide repeats were found to be highly predominant. Mononucleotide repeats were found to be underrepresented in majority of Tombusviridae genomes. Poly G and Poly C repeats were more abundant as compared to poly A or poly T nucleotides. TG/GT and AG/CA was the most abundant dinucleotide repeat motif observed in Tombusviridae genomes. Repeats larger than trinucleotide were never found in these viral genomes. Comparative study of relative abundance and density of microsatellite among available RNA and DNA viral genomes indicated that simple repeats were lower than many RNA virus genomes. To our knowledge, this is the first analysis of microsatellites occurring in Tombusviridae genomes. Characterization of such variations in repeat sequences would be important in deciphering the origin, mutational processes, and role of repeat sequences in viral genomes.

Genome wide survey of microsatellites in ssDNA viruses infecting vertebrates

Microsatellites or Simple Sequence Repeats (SSRs) are tandem iterations of one to six base pairs, non-randomly distributed throughout prokaryotic and eukaryotic genomes. Limited knowledge is available about distribution of microsatellites in single stranded DNA (ssDNA) viruses, particularly vertebrate infecting viruses. We studied microsatellite distribution in 118 ssDNA virus genomes belonging to three families of vertebrate infecting viruses namely Circoviridae, Parvoviridae, and Anelloviridae, and found that microsatellites constitute an important component of these virus genomes. Mononucleotide repeats were predominant followed by dinucleotide and trinucleotide repeats. A strong positive relationship existed between number of mononucleotide repeats and genome size among all the three virus families. A similar relationship existed for the occurrence of DTTPH (di-, tri-, tetra-, penta- and hexa-nucleotide) repeats in the families Anelloviridae and Parvoviridae only. Relative abundance and relative density of mononucleotide repeats showed a strong positive relationship with genome size in Circoviridae and Parvoviridae. However, in the case of DTTPH repeats, these features showed a strong relationship with genome size in Circoviridae only. On the other hand, relative microsatellite abundance and relative density of mononucleotide repeats were negatively correlated with GC content (%) in Parvoviridae genomes. On the basis of available annotations, our analysis revealed maximum occurrence of mononucleotide as well as DTTPH repeats in the coding regions of these virus genomes. Interestingly, after normalizing the length of the coding and non-coding regions of each virus genome, we found relative density of microsatellites much higher in the non-coding regions. We understand that the present study will help in the better characterization of the stability, genome organization and evolution of these virus classes and may provide useful leads to decipher the etiopathogenesis of these viruses.

Identification and characterization of microsatellite from Alternaria brassicicola to assess cross-species transferability and utility as a diagnostic marker.

Alternaria blight caused by Alternaria brassicicola (Schwein.) Wiltshire and A. brassicae (Berk.) Sacc., is one of the most important disease of rapeseed-mustard, characterized by the formation of spots on leaves, stem, and siliquae with premature defoliation and stunting of growth. These two species are very difficult to differentiate based on disease symptoms or spore morphology. Therefore, the aim of present investigation was to identify and characterize transferable microsatellite loci from A. brassicicola to A. brassicae for the development of diagnostic marker. A total of 8,457 microsatellites were identified from transcript sequences of A. brassicicola. The average density of microsatellites was one microsatellite per 1.94 kb of transcript sequence screened. The most frequent repeat was tri-nucleotide (74.03 %), whereas penta-nucleotide (1.14 %) was least frequent. Among amino acids, arginine (13.11 %) showed maximum abundance followed by lysine (10.11 %). A total of 32 alleles were obtained across the 31 microsatellite loci for the ten isolates of A. brassicicola. In cross-species amplifications, 5 of the 31 markers amplified the corresponding microsatellite regions in twenty isolates of A. brassicae and showed monomorphic banding pattern. Microsatellite locus ABS28 was highly specific for A. brassicicola, as no amplification was observed from twenty-nine other closely related taxa. Primer set, ABS28F/ABS28R, amplified a specific amplicon of 380 bp from all A. brassicicola isolates. Standard curves were generated for A. brassicicola isolate using SYBR Green I fluorescent dye for detection of amplification in real-time PCR assay. The lowest detection limit of assay was 0.01 ng. Thus, the primer set can be used as diagnostic marker to discriminate and diagnose A. brassicicola from synchronously occurring fungus, A. brassicae associated with rapeseed and mustard.

Genome wide survey and analysis of small repetitive sequences in caulimoviruses

Microsatellites are known to exhibit ubiquitous presence across all kingdoms of life including viruses. Members of the Caulimoviridae family severely affect growth of vegetable and fruit plants and reduce economic yield in diverse cropping systems worldwide. Here, we analyzed the nature and distribution of both simple and complex microsatellites present in complete genome of 44 species of Caulimoviridae. Our results showed, in all analyzed genomes, genome size and GC content had a weak influence on number, relative abundance and relative density of microsatellites, respectively. For each genome, mono- and dinucleotide repeats were found to be highly predominant and are overrepresented in genome of majority of caulimoviruses. AT/TA and GAA/AAG/AGA was the most abundant di- and trinucleotide repeat motif, respectively. Repeats larger than trinucleotide were rarely found in these genomes. Comparative study of occurrence, abundance and density of microsatellite among available RNA and DNA viral genomes indicated that simple repeats were least abundant in genomes of caulimoviruses. Polymorphic repeats even though rare were observed in the large intergenic region of the genome, indicating strand slippage and/or unequal recombination processes do occur in caulimoviruses. To our knowledge, this is the first analysis of microsatellites occurring in any dsDNA viral genome. Characterization of such variations in repeat sequences would be important in deciphering the origin, mutational processes, and role of repeat sequences in viral genomes.

Microsatellite Tandem Repeats Are Abundant in Human Promoters and Are Associated with Regulatory Elements

Tandem repeats are genomic elements that are prone to changes in repeat number and are thus often polymorphic. These sequences are found at a high density at the start of human genes, in the gene’s promoter. Increasing empirical evidence suggests that length variation in these tandem repeats can affect gene regulation. One class of tandem repeats, known as microsatellites, rapidly alter in repeat number. Some of the genetic variation induced by microsatellites is known to result in phenotypic variation. Recently, our group developed a novel method for measuring the evolutionary conservation of microsatellites, and with it we discovered that human microsatellites near transcription start sites are often highly conserved. In this study, we examined the properties of microsatellites found in promoters. We found a high density of microsatellites at the start of genes. We showed that microsatellites are statistically associated with promoters using a wavelet analysis, which allowed us to test for associations on multiple scales and to control for other promoter related elements. Because promoter microsatellites tend to be G/C rich, we hypothesized that G/C rich regulatory elements may drive the association between microsatellites and promoters. Our results indicate that CpG islands, G-quadruplexes (G4) and untranslated regulatory regions have highly significant associations with microsatellites, but controlling for these elements in the analysis does not remove the association between microsatellites and promoters. Due to their intrinsic lability and their overlap with predicted functional elements, these results suggest that many promoter microsatellites have the potential to affect human phenotypes by generating mutations in regulatory elements, which may ultimately result in disease. We discuss the potential functions of human promoter microsatellites in this context.

The X chromosome, heterochromatin and speciation in malaria mosquitoes

The available data suggest that the X chromosome of Anopheles had originated independently from the X chromosome of Drosophila. In order to gain insights into a possible role of the X chromosome in speciation of malaria mosquitoes, we studied the pattern of rearrangements, genomic landscapes and heterochromatin variations among closely and distantly related species. • Our cytogenetic analysis of the An. gambiae species complex showed fixed differences in the amount and pattern of the X heterochromatin among sibling species as well as between the M and S forms (Fig. 1). Interestingly, the low-recombination pericentric region displayed the high level of polymorphism in the size of heterochromatin and the rDNA locus (Fig. 2). • The largest region of the high genomic divergence between the incipient species (the M and S forms) co-localizes with the heterochromatin of the An. gambiae X chromosome (Fig. 3). • Our comparative physical mapping of distantly related malaria mosquito species identified the fastest rate of inversion fixation on the X chromosome despite the paucity of inversion polymorphism (Fig. 4). • The analysis of the An. gambiae genome demonstrated the highest density of transposable elements, microsatellites, minisatellites, and satellites in the X chromosome (Fig. 5). • The X chromosome is enriched in genes that may be involved in premating isolation, such as genes encoding for proteins with molecular and signal transduction activity (Fig. 6). Thus, our study points out to the elevated evolutionary plasticity of the euchromatic gene order and heterochromatin structure of the X chromosome suggesting a possible role of the sex chromosome in speciation of malaria mosquitoes. An. gambiae SUA 2La (M) An. gambiae Pimperena (S) An. gambiae Akron (M) An. gambiae Kisumu (S) Pericentric heterochromatin exhibits inter-specific differences An. merus An. quadriannulatus An. arabiensis An. gambiae Zanu (S) Fig. 1. Heterochromatin patterns observed after staining with DAPI. Arrows indicate heterochromatin (darker areas) exhibiting inter and intra-specific differences. While the M forms (Sua, Akron) exhibit single large bands (A, B), S forms (Zanu, Pimperena, Kisumu) exhibit a secondary heterochromatic band in (C-E). Sibling species (FH) also exhibit variation in heterochromatin patterns. An. gambiae Kisumu (S) An. gambiae Akron (M)

Differential distribution of compound microsatellites in various Human Immunodeficiency Virus Type 1 complete genomes

Compound microsatellites consist of two or more individual microsatellites, and may originate from dynamic mutations or imperfection of microsatellites. Previous studies have found microsatellites were present in 81 completed Human Immunodeficiency Virus Type 1 (HIV-1) genomes, suggesting compound microsatellites may exist in viral genomes. However, up to now, compound microsatellites have not been analyzed in any viral genomes. We identified and characterized 238 compound microsatellites in 81 completed HIV-1 genomes. About 0–24.24% of all microsatellites could be categorized as compound microsatellites. Compound microsatellite distribution is very different in two aspects between diverse HIV-1 genomes. First, the number and motifs of compound microsatellites are variable between surveyed genomes. Second, the relative abundance and relative density of compound microsatellites exhibit very significant differences between these surveyed genomes, respectively. The relative abundance and relative density of compound microsatellites were weakly correlated with genome size and microsatellite density. We observed a more dynamic picture of compound microsatellites than previously reported in eukaryotes. This might be attributed to the lack of proofreading in HIV-1 genomes, as it has been demonstrated that the loss of polymerase proofreading activity can greatly enhance the mutation rate of microsatellites.

A comparative in silico analysis on frequency and distribution of microsatellites in coding regions of three formae speciales of Fusarium oxysporum and development of EST-SSR markers for polymorphism studies

Fusarium oxysporum is a ubiquitous species complex of soil-borne plant pathogens comprising of many different formae speciales, each characterized by a high degree of host specificity. In the present investigation, we surveyed microsatellites in the available express sequence tags and transcript sequences of three formae speciales of F.oxysporum viz. melonis (Fom), cucumerium (Foc), and lycopersici (Fol). The relative abundance and density of microsatellites were higher in Fom when compared with Foc and Fol. Thirty microsatellite primers were designed, ten from each forma specialis, for genetic characterization of F.oxysporum isolates belonging to five formae speciales. Of the 30 primers, only 14 showed amplification. A total of 28 alleles were amplified by 14 primers with an average of two alleles per marker. Eight markers showed 100% polymorphism. The markers were found to be more polymorphic (47%) in Fol as compared to Fom and Foc; however, polymorphic information content was the maximum (0.899) in FocSSR-3. Nine polymorphic markers obtained in this study clearly demonstrate the utility of newly developed markers in establishing genetic relationships among different isolates of F.oxysporum.