Functional Mechanisms of Microsatellite DNA in Eukaryotic Genomes

Familial cases with adult-onset FGF23-related hypophosphatemic osteomalacia -A PHEX 3'-UTR change as a possible cause

Excessive actions of FGF23 cause several kinds of hypophosphatemic rickets/osteomalacia. It is possible that there still remain unknown causes or mechanisms for FGF23-related hypophosphatemic diseases. We report two male cousins who had been suffering form FGF23-related hypophosphatemic osteomalacia. Sequencing of exons and exon-intron junctions of known causative genes for FGF23-related hypophosphatemic diseases and whole genome sequencing were conducted. Luciferase assay was used to evaluate the effect of a detected nucleotide change on mRNA stability. Two cousins showed hypophosphatemia with impaired proximal tubular phosphate reabsorption and high FGF23. Serum phosphate of their mothers was within the reference range. Exome sequencing of the proband detected no mutations. Whole genome sequencing of the patients and their mothers identified a nucleotide change in the 3'-UTR of phosphate-regulating gene with homologies to endopeptidases on the X chromosome (PHEX) gene (c.*1280_*1287dupGTGTGTGT) which is heterozygous in the mothers and hemizygous in the patients. While sixteen is the most prevalent number of GT repeats, this family had twenty repeats. Luciferase assay indicated that mRNA with 3'-UTR of PHEX with 20 GT repeats was more unstable than that with 16 repeats. Sequencing of exons and exon-intron junctions of known causative genes for FGF23-related hypophosphatemic diseases cannot identify all the genetic causes. Our results strongly suggest that changes of PHEX expression by a nucleotide change in the 3'-UTR is a novel mechanism of FGF23-related hypophosphatemic osteomalacia.

Chromosomal organization of different repetitive sequences in four wasp species of the genus Trypoxylon Latreille (Hymenoptera: Crabronidae) and insights into the composition of wasp telomeres

This study characterizes the chromosomal organization of DNA repetitive sequences and the karyotypic evolution in four representatives of the solitary wasp genus Trypoxylon using conventional and molecular cytogenetic techniques. Our findings present the first cytogenetic data for Trypoxylon rogenhoferi (2n = 30) and Trypoxylon albonigrum (2n = 32), while the karyotypes of Trypoxylon nitidum (2n = 30) and Trypoxylon lactitarse (2n = 30) were similar to those previously described. Fluorochrome staining and microsatellite distribution data revealed differences in the constitutive heterochromatin composition among species. Trypoxylon nitidum and T. albonigrum exhibited one major rDNA cluster, potentially representing an ancestral pattern for aculeate Hymenoptera, while T. rogenhoferi and T. lactitarse showed two pericentromeric rRNA gene sites, suggesting amplification events in their ancestral clade. The (TCAGG)n motif hybridized in the terminal regions of the chromosomes in all four Trypoxylon species, which may suggest that this sequence represents DNA telomeric repeat. Notably, the presence of this repetitive sequence in the centromeric regions of certain chromosome pairs in two species supports the hypothesis of chromosomal fusions or inversions in the ancestral karyotype of Trypoxylon. The study expands the chromosomal mapping data of repetitive sequences in wasps and offers insights into the dynamic evolutionary landscape of karyotypes in these insects.

Comparative cytogenetics of microsatellite distribution in two tetra fishes Astyanax bimaculatus (Linnaeus, 1758) and Psalidodon scabripinnis (Jenyns, 1842)

Background

The main cytogenetic studies of the Characidae family comprise the genera Astyanax and Psalidodon involving the use of repetitive DNA probes. However, for the microsatellite classes, studies are still scarce and the function of these sequences in the genome of these individuals is still not understood. Thus, we aimed to analyze and compare the distribution of microsatellite sequences in the species Astyanax bimaculatus and Psalidodon scabripinnis.

Methods

We collected biopsies from the fins of A. bimaculatus and P. scabripinnis to perform cell culture, followed by chromosome extraction, and mapped the distribution of 14 microsatellites by FISH in both species.

Results and Discussion

The diploid number observed for both species was 2n = 50, with an acrocentric B microchromosome in A. bimaculatus and a metacentric B chromosome in P. scabripinnis. Regarding FISH, 11 probes hybridized in the karyotype of A. bimaculatus mainly in centromeric regions, and 13 probes hybridized in P. scabripinnis, mainly in telomeric regions, in addition to a large accumulation of microsatellite hybridization on its B chromosome.

Conclusion

Comparative FISH mapping of 14 microsatellite motifs revealed different patterns of distribution both in autosomes and supernumerary chromosomes of A. bimaculatus and P. scabripinnis, suggesting independent evolutionary processes in each of these species, representing excellent data on chromosome rearrangements and cytotaxonomy.

Solution Structure of Poly(UG) RNA

Poly(UG) or "pUG" RNAs are UG or GU dinucleotide repeat sequences which are highly abundant in eukaryotes. Post-transcriptional addition of pUGs to RNA 3' ends marks mRNAs as vectors for gene silencing in C. elegans. We previously determined the crystal structure of pUG RNA bound to the ligand N-methyl mesoporphyrin IX (NMM), but the structure of free pUG RNA is unknown. Here we report the solution structure of the free pUG RNA (GU)12, as determined by nuclear magnetic resonance spectroscopy and small and wide-angle x-ray scattering (NMR-SAXS-WAXS). The low complexity sequence and 4-fold symmetry of the structure result in overlapped NMR signals that complicate chemical shift assignment. We therefore utilized single site-specific deoxyribose modifications which did not perturb the structure and introduced well-resolved methylene signals that are easily identified in NMR spectra. The solution structure ensemble has a root mean squared deviation (RMSD) of 0.62 Å and is a compact, left-handed quadruplex with a Z-form backbone, or "pUG fold." Overall, the structure agrees with the crystal structure of (GU)12 bound to NMM, indicating the pUG fold is unaltered by docking of the NMM ligand. The solution structure reveals conformational details that could not be resolved by x-ray crystallography, which explain how the pUG fold can form within longer RNAs.

FOXP3 recognizes microsatellites and bridges DNA through multimerization

FOXP3 is a transcription factor that is essential for the development of regulatory T cells, a branch of T cells that suppress excessive inflammation and autoimmunity1-5. However, the molecular mechanisms of FOXP3 remain unclear. Here we here show that FOXP3 uses the forkhead domain-a DNA-binding domain that is commonly thought to function as a monomer or dimer-to form a higher-order multimer after binding to TnG repeat microsatellites. The cryo-electron microscopy structure of FOXP3 in a complex with T3G repeats reveals a ladder-like architecture, whereby two double-stranded DNA molecules form the two 'side rails' bridged by five pairs of FOXP3 molecules, with each pair forming a 'rung'. Each FOXP3 subunit occupies TGTTTGT within the repeats in a manner that is indistinguishable from that of FOXP3 bound to the forkhead consensus motif (TGTTTAC). Mutations in the intra-rung interface impair TnG repeat recognition, DNA bridging and the cellular functions of FOXP3, all without affecting binding to the forkhead consensus motif. FOXP3 can tolerate variable inter-rung spacings, explaining its broad specificity for TnG-repeat-like sequences in vivo and in vitro. Both FOXP3 orthologues and paralogues show similar TnG repeat recognition and DNA bridging. These findings therefore reveal a mode of DNA recognition that involves transcription factor homomultimerization and DNA bridging, and further implicates microsatellites in transcriptional regulation and diseases.

Current progress of immune checkpoint inhibitors for advanced colorectal cancer: concentrating on the efficacy improvement

Immune checkpoint inhibitors (ICIs) have paved a new pathway and revolutionized cancer treatment. Currently, ICIs have been extensively used for patients with advanced colorectal cancer (CRC), especially those harboring microsatellite instability (MSI). However, the efficacy of ICIs varies tremendously in different individuals, and some patients may not benefit from ICIs, which limits their clinical application. How to improve the efficacy of ICIs is an important issue to be solved. On the one hand, it is urgent to discover the predictive biomarkers to accurately screen the patients who gain benefit from ICIs, like microsatellite stability, tumor mutation burden (TMB), DNA polymerase ε/DNA polymerase δ1 mutations, and the expression of programmed death-ligand 1 (PD-L1). The rational use of these biomarkers will help clinicians identify suitable candidates who will benefit from ICI treatment, thereby improving therapeutic efficiency. Additionally, it is vital to design combination therapeutic strategies for optimizing the therapeutic effectiveness of ICIs. Nowadays, treatment strategies like chemotherapy, radiotherapy, targeted therapy along with ICIs, have helped improve the therapeutic effectiveness of ICIs. In this review, we have focused on the recent advancements in the predictive biomarkers and combination therapeutic strategies with ICIs for colorectal cancer.

FoxP3 recognizes microsatellites and bridges DNA through multimerization

FoxP3 is a transcription factor (TF) essential for development of regulatory T cells (Tregs), a branch of T cells that suppress excessive inflammation and autoimmunity 1-5 . Molecular mechanisms of FoxP3, however, remain elusive. We here show that FoxP3 utilizes the Forkhead domain--a DNA binding domain (DBD) that is commonly thought to function as a monomer or dimer--to form a higher-order multimer upon binding to T n G repeat microsatellites. A cryo-electron microscopy structure of FoxP3 in complex with T 3 G repeats reveals a ladder-like architecture, where two double-stranded DNA molecules form the two "side rails" bridged by five pairs of FoxP3 molecules, with each pair forming a "rung". Each FoxP3 subunit occupies TGTTTGT within the repeats in the manner indistinguishable from that of FoxP3 bound to the Forkhead consensus motif (FKHM; TGTTTAC). Mutations in the "intra-rung" interface impair T n G repeat recognition, DNA bridging and cellular functions of FoxP3, all without affecting FKHM binding. FoxP3 can tolerate variable "inter-rung" spacings, explaining its broad specificity for T n G repeat-like sequences in vivo and in vitro . Both FoxP3 orthologs and paralogs show similar T n G repeat recognition and DNA bridging. These findings thus reveal a new mode of DNA recognition that involves TF homo-multimerization and DNA bridging, and further implicates microsatellites in transcriptional regulation and diseases.

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 (≥ 50 M% 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.

DHX9/DNA-tandem repeat-dependent downregulation of ciRNA-Fmn1 in the dorsal horn is required for neuropathic pain

Circular RNAs (ciRNAs) are emerging as new players in the regulation of gene expression. However, how ciRNAs are involved in neuropathic pain is poorly understood. Here, we identify the nervous-tissue-specific ciRNA-Fmn1 and report that changes in ciRNA-Fmn1 expression in spinal cord dorsal horn neurons play a key role in neuropathic pain after nerve injury. ciRNA-Fmn1 was significantly downregulated in ipsilateral dorsal horn neurons after peripheral nerve injury, at least in part because of a decrease in DNA helicase 9 (DHX9), which regulates production of ciRNA-Fmn1 by binding to DNA-tandem repeats. Blocking ciRNA-Fmn1 downregulation reversed nerve-injury-induced reductions in both the binding of ciRNA-Fmn1 to the ubiquitin ligase UBR5 and the level of ubiquitination of albumin (ALB), thereby abrogating the nerve-injury-induced increase of ALB expression in the dorsal horn and attenuating the associated pain hypersensitivities. Conversely, mimicking downregulation of ciRNA-Fmn1 in naïve mice reduced the UBR5-controlled ubiquitination of ALB, leading to increased expression of ALB in the dorsal horn and induction of neuropathic-pain-like behaviors in naïve mice. Thus, ciRNA-Fmn1 downregulation caused by changes in binding of DHX9 to DNA-tandem repeats contributes to the genesis of neuropathic pain by negatively modulating UBR5-controlled ALB expression in the dorsal horn.

Plant BBR/BPC transcription factors: unlocking multilayered regulation in development, stress and immunity

MAIN CONCLUSION

This review provides a detailed structural and functional understanding of BBR/BPC TF, their conservation across the plant lineage, and their comparative study with animal GAFs. Plant-specific Barley B Recombinant/Basic PentaCysteine (BBR/BPC) transcription factor (TF) family binds to "GA" repeats similar to animal GAGA Factors (GAFs). These GAGA binding proteins are among the few TFs that regulate the genes at multiple steps by modulating the chromatin structure. The hallmark of the BBR/BPC TF family is the presence of a conserved C-terminal region with five cysteine residues. In this review, we present: first, the structural distinct yet functional similar relation of plant BBR/BPC TF with animal GAFs, second, the conservation of BBR/BPC across the plant lineage, third, their role in planta, fourth, their potential interacting partners and structural insights. We conclude that BBR/BPC TFs have multifaceted roles in plants. Besides the earliest identified function in homeotic gene regulation and developmental processes, presently BBR/BPC TFs were identified in hormone signaling, stress, circadian oscillation, and sex determination processes. Understanding how plants' development and stress processes are coordinated is central to divulging the growth-immunity trade-off regulation. The BBR/BPC TFs may hold keys to divulge the interactions between development and immunity. Moreover, the conservation of BBR/BPC across plant lineage makes it an evolutionary vital gene family. Consequently, BBR/BPCs are prospective to attract the increasing attention of the scientific communities as they are probably at the crossroads of diverse fundamental processes.

Cellular barcoding: From developmental tracing to anti-tumor drug discovery

Clonal evolution has gained immense attention in explaining cancer cell status, history, and fate during cancer progression. Current single-cell or spatial transcriptome technologies have broadened our understanding of various mechanisms underlying cancer initiation, relapse, and drug resistance. However, technical challenges still hinder a better understanding of the dynamics of distinctive phenotypic states and abnormal trajectories from normal physiological transition to malignant stages. Cellular barcoding enabled lineage tracing on parallelly massive cells at single-cell resolution through different mechanisms lately, enabling new insights into exploring developmental trajectories, cancer progression, and targeted therapies. This review summarizes the latest noteworthy and robust strategies for different types of cellular barcodes. To introduce the major characteristics, advantages and limitations of these different strategies, this review will further guide in choosing or improving cellular barcoding technologies and their applications in cancer research.

Are scattered microsatellites weak chromosomal markers? Guided mapping reveals new insights into Trachelyopterus (Siluriformes: Auchenipteridae) diversity

The scattered distribution pattern of microsatellites is a challenging problem in fish cytogenetics. This type of array hinders the identification of useful patterns and the comparison between species, often resulting in over-limited interpretations that only label it as "scattered" or "widely distributed". However, several studies have shown that the distribution pattern of microsatellites is non-random. Thus, here we tested whether a scattered microsatellite could have distinct distribution patterns on homeologous chromosomes of closely related species. The clustered sites of 18S and 5S rDNA, U2 snRNA and H3/H4 histone genes were used as a guide to compare the (GATA)n microsatellite distribution pattern on the homeologous chromosomes of six Trachelyopterus species: T. coriaceus and Trachelyopterus aff. galeatus from the Araguaia River basin; T. striatulus, T. galeatus and T. porosus from the Amazonas River basin; and Trachelyopterus aff. coriaceus from the Paraguay River basin. Most species had similar patterns of the (GATA)n microsatellite in the histone genes and 5S rDNA carriers. However, we have found a chromosomal polymorphism of the (GATA)n sequence in the 18S rDNA carriers of Trachelyopterus galeatus, which is in Hard-Weinberg equilibrium and possibly originated through amplification events; and a chromosome polymorphism in Trachelyopterus aff. galeatus, which combined with an inversion polymorphism of the U2 snRNA in the same chromosome pair resulted in six possible cytotypes, which are in Hardy-Weinberg disequilibrium. Therefore, comparing the distribution pattern on homeologous chromosomes across the species, using gene clusters as a guide to identify it, seems to be an effective way to further the analysis of scattered microsatellites in fish cytogenetics.

Short tandem repeats are important contributors to silencer elements in T cells

The action of cis-regulatory elements with either activation or repression functions underpins the precise regulation of gene expression during normal development and cell differentiation. Gene activation by the combined activities of promoters and distal enhancers has been extensively studied in normal and pathological contexts. In sharp contrast, gene repression by cis-acting silencers, defined as genetic elements that negatively regulate gene transcription in a position-independent fashion, is less well understood. Here, we repurpose the STARR-seq approach as a novel high-throughput reporter strategy to quantitatively assess silencer activity in mammals. We assessed silencer activity from DNase hypersensitive I sites in a mouse T cell line. Identified silencers were associated with either repressive or active chromatin marks and enriched for binding motifs of known transcriptional repressors. CRISPR-mediated genomic deletions validated the repressive function of distinct silencers involved in the repression of non-T cell genes and genes regulated during T cell differentiation. Finally, we unravel an association of silencer activity with short tandem repeats, highlighting the role of repetitive elements in silencer activity. Our results provide a general strategy for genome-wide identification and characterization of silencer elements.

G-QINDER Tool: Bioinformatically Predicted Formation of Different Four-Stranded DNA Motifs from (GT)n and (GA)n Repeats

The recently introduced semi-orthogonal system of nucleic acid imaging offers a greatly improved method of identifying DNA sequences that are capable of adopting noncanonical structures. This paper uses our newly developed G-QINDER tool to identify specific repeat sequences that adopt unique structural motifs in DNA: TG and AG repeats. The structures were found to adopt a left-handed G-quadruplex form under extreme crowding conditions and a unique tetrahelical motif under certain other conditions. The tetrahelical structure likely consists of stacked AGAG-tetrads but, unlike G-quadruplexes, their stability does not appear to be dependent on the type of monovalent cation present. The occurrence of TG and AG repeats in genomes is not rare, and they are also found frequently in the regulatory regions of nucleic acids, so it is reasonable to assume that putative structural motifs, like other noncanonical forms, could play an important regulatory role in cells. This hypothesis is supported by the structural stability of the AGAG motif; its unfolding can occur even at physiological temperatures since the melting temperature is primarily dependent on the number of AG repeats in the sequence.

Comprehensive Comparative Analysis Sheds Light on the Patterns of Microsatellite Distribution across Birds Based on the Chromosome-Level Genomes

Microsatellites (SSRs) are widely distributed in the genomes of organisms and are an important genetic basis for genome evolution and phenotypic adaptation. Although the distribution patterns of microsatellites have been investigated in many phylogenetic lineages, they remain unclear within the morphologically and physiologically diverse avian clades. Here, based on high-quality chromosome-level genomes, we examined the microsatellite distribution patterns for 53 birds from 16 orders. The results demonstrated that each type of SSR had the same ratio between taxa. For example, the frequency of imperfect SSRs (I-SSRs) was 69.90-84.61%, while perfect SSRs (P-SSRs) were 14.86-28.13% and compound SSRs (C-SSRs) were 0.39-2.24%. Mononucleotide SSRs were dominant for perfect SSRs (32.66-76.48%) in most bird species (98.11%), and A(n) was the most abundant repeat motifs of P-SSRs in all birds (5.42-68.22%). Our study further confirmed that the abundance and diversity of microsatellites were less effected by evolutionary history but its length. The number of P-SSRs decreased with increasing repeat times, and longer P-SSRs motifs had a higher variability coefficient of the repeat copy number and lower diversity, indicating that longer motifs tended to have more stable preferences in avian genomes. We also found that P-SSRs were mainly distributed at the gene ends, and the functional annotation for these genes demonstrated that they were related to signal transduction and cellular process. In conclusion, our research provided avian SSR distribution patterns, which will help to explore the genetic basis for phenotypic diversity in birds.

Gene-Environment Interactions in Repeat Expansion Diseases: Mechanisms of Environmentally Induced Repeat Instability

Short tandem repeats (STRs) are units of 1-6 base pairs that occur in tandem repetition to form a repeat tract. STRs exhibit repeat instability, which generates expansions or contractions of the repeat tract. Over 50 diseases, primarily affecting the central nervous system and muscles, are characterized by repeat instability. Longer repeat tracts are typically associated with earlier age of onset and increased disease severity. Environmental exposures are suspected to play a role in the pathogenesis of repeat expansion diseases. Here, we review the current knowledge of mechanisms of environmentally induced repeat instability in repeat expansion diseases. The current evidence demonstrates that environmental factors modulate repeat instability via DNA damage and induction of DNA repair pathways, with distinct mechanisms for repeat expansion and contraction. Of particular note, oxidative stress is a key mediator of environmentally induced repeat instability. The preliminary evidence suggests epigenetic modifications as potential mediators of environmentally induced repeat instability. Future research incorporating an array of environmental exposures, new human cohorts, and improved model systems, with a continued focus on cell-types, tissues, and critical windows, will aid in identifying mechanisms of environmentally induced repeat instability. Identifying environmental modulators of repeat instability and their mechanisms of action will inform preventions, therapies, and public health measures.

Mutation and selection processes regulating short tandem repeats give rise to genetic and phenotypic diversity across species

Short tandem repeats (STRs) are units of 1-6 bp that repeat in a tandem fashion in DNA. Along with single nucleotide polymorphisms and large structural variations, they are among the major genomic variants underlying genetic, and likely phenotypic, divergence. STRs experience mutation rates that are orders of magnitude higher than other well-studied genotypic variants. Frequent copy number changes result in a wide range of alleles, and provide unique opportunities for modulating complex phenotypes through variation in repeat length. While classical studies have identified key roles of individual STR loci, the advent of improved sequencing technology, high-quality genome assemblies for diverse species, and bioinformatics methods for genome-wide STR analysis now enable more systematic study of STR variation across wide evolutionary ranges. In this review, we explore mutation and selection processes that affect STR copy number evolution, and how these processes give rise to varying STR patterns both within and across species. Finally, we review recent examples of functional and adaptive changes linked to STRs.

Genome-wide evaluation of the effect of short tandem repeat variation on local DNA methylation

Short tandem repeats (STRs) contribute significantly to genetic diversity in humans, including disease-causing variation. Although the effect of STR variation on gene expression has been extensively assessed, their impact on epigenetics has been poorly studied and limited to specific genomic regions. Here, we investigated the hypothesis that some STRs act as independent regulators of local DNA methylation in the human genome and modify risk of common human traits. To address these questions, we first analyzed two independent data sets comprising PCR-free whole-genome sequencing (WGS) and genome-wide DNA methylation levels derived from whole-blood samples in 245 (discovery cohort) and 484 individuals (replication cohort). Using genotypes for 131,635 polymorphic STRs derived from WGS using HipSTR, we identified 11,870 STRs that associated with DNA methylation levels (mSTRs) of 11,774 CpGs (Bonferroni P < 0.001) in our discovery cohort, with 90% successfully replicating in our second cohort. Subsequently, through fine-mapping using CAVIAR we defined 585 of these mSTRs as the likely causal variants underlying the observed associations (fm-mSTRs) and linked a fraction of these to previously reported genome-wide association study signals, providing insights into the mechanisms underlying complex human traits. Furthermore, by integrating gene expression data, we observed that 12.5% of the tested fm-mSTRs also modulate expression levels of nearby genes, reinforcing their regulatory potential. Overall, our findings expand the catalog of functional sequence variants that affect genome regulation, highlighting the importance of incorporating STRs in future genetic association analysis and epigenetics data for the interpretation of trait-associated variants.

MicroRNA Identification, Target Prediction, and Validation for Crop Improvement

Micro-RNAs (mi-RNAs) are regulatory elements that play a vital role in the growth, development, and metabolic regulation of plants. In current research, the isolation of miRNAs is a tedious and difficult task using in vitro methods. However, recent exploration into the remarkably highly conserved nature of nucleotide sequences of miRNAs assists in the identification of miRNAs in plant species through homologous approaches. Here, we describe the in silico-based method for identification of miRNAs from the EST database which is emerging as a faster and more reliable approach along with the development of miRNA-SSR markers. This approach has the potential to accelerate research into the regulation of gene expression in various plant species such as tea, potato, tomato, tobacco, and orphan crops like cluster bean.

The distinct clinical trajectory, metastatic sites, and immunobiology of microsatellite-instability-high cancers

Microsatellite-instability-high (MSI-H) cancers form a spectrum of solid organ tumors collectively known as Lynch Syndrome cancers, occurring not only in a subset of colorectal, endometrial, small bowel, gastric, pancreatic, and biliary tract cancers but also in prostate, breast, bladder, and thyroid cancers. Patients with Lynch Syndrome harbor germline mutations in mismatch repair genes, with a high degree of genomic instability, leading to somatic hypermutations and, therefore, oncogenesis and cancer progression. MSI-H cancers have unique clinicopathological characteristics compared to their microsatellite-stable (MSS) counterparts, marked by a higher neoantigen load, immune cell infiltration, and a marked clinical response to immune checkpoint blockade. Patients with known Lynch Syndrome may be detected early through surveillance, but some patients present with disseminated metastatic disease. The treatment landscape of MSI-H cancers, especially colorectal cancers, has undergone a paradigm shift and remains to be defined, with immune checkpoint blockade coming to the forefront of treatment strategies in the stage IV setting. We summarize in this review the clinical features of MSI-H cancers with a specific interest in the pattern of spread or recurrence, disease trajectory, and treatment strategies. We also summarize the tumor-immune landscape and genomic profile of MSI-H cancers and potential novel therapeutic strategies.

Tandem repeats ubiquitously flank and contribute to translation initiation sites

Background

While the evolutionary divergence of cis-regulatory sequences impacts translation initiation sites (TISs), the implication of tandem repeats (TRs) in TIS selection remains largely elusive. Here, we employed the TIS homology concept to study a possible link between TRs of all core lengths and repeats with TISs.

Methods

Human, as reference sequence, and 83 other species were selected, and data was extracted on the entire protein-coding genes (n = 1,611,368) and transcripts (n = 2,730,515) annotated for those species from Ensembl 102. Following TIS identification, two different weighing vectors were employed to assign TIS homology, and the co-occurrence pattern of TISs with the upstream flanking TRs was studied in the selected species. The results were assessed in 10-fold cross-validation.

Results

On average, every TIS was flanked by 1.19 TRs of various categories within its 120 bp upstream sequence, per species. We detected statistically significant enrichment of non-homologous human TISs co-occurring with human-specific TRs. On the contrary, homologous human TISs co-occurred significantly with non-human-specific TRs. 2991 human genes had at least one transcript, TIS of which was flanked by a human-specific TR. Text mining of a number of the identified genes, such as CACNA1A, EIF5AL1, FOXK1, GABRB2, MYH2, SLC6A8, and TTN, yielded predominant expression and functions in the human brain and/or skeletal muscle.

Conclusion

We conclude that TRs ubiquitously flank and contribute to TIS selection at the trans-species level. Future functional analyses, such as a combination of genome editing strategies and in vitro protein synthesis may be employed to further investigate the impact of TRs on TIS selection.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12863-022-01075-5.

Microsatellite Variation in the Most Devastating Beetle Pests (Coleoptera: Curculionidae) of Agricultural and Forest Crops

Weevils, classified in the family Curculionidae (true weevils), constitute a group of phytophagous insects of which many species are considered significant pests of crops. Within this family, the red palm weevil (RPW), Rhynchophorus ferrugineus, has an integral role in destroying crops and has invaded all countries of the Middle East and many in North Africa, Southern Europe, Southeast Asia, Oceania, and the Caribbean Islands. Simple sequence repeats (SSRs), also termed microsatellites, have become the DNA marker technology most applied to study population structure, evolution, and genetic diversity. Although these markers have been widely examined in many mammalian and plant species, and draft genome assemblies are available for many species of true weevils, very little is yet known about SSRs in weevil genomes. Here we carried out a comparative analysis examining and comparing the relative abundance, relative density, and GC content of SSRs in previously sequenced draft genomes of nine true weevils, with an emphasis on R. ferrugineus. We also used Illumina paired-end sequencing to generate draft sequence for adult female RPW and characterized it in terms of perfect SSRs with 1–6 bp nucleotide motifs. Among weevil genomes, mono- to trinucleotide SSRs were the most frequent, and mono-, di-, and hexanucleotide SSRs exhibited the highest GC content. In these draft genomes, SSR number and genome size were significantly correlated. This work will aid our understanding of the genome architecture and evolution of Curculionidae weevils and facilitate exploring SSR molecular marker development in these species.

Non-canonical DNA/RNA structures associated with the pathogenesis of Fragile X-associated tremor/ataxia syndrome and Fragile X syndrome

Fragile X-associated tremor/ataxia syndrome (FXTAS) and fragile X syndrome (FXS) are primary examples of fragile X-related disorders (FXDs) caused by abnormal expansion of CGG repeats above a certain threshold in the 5′-untranslated region of the fragile X mental retardation (FMR1) gene. Both diseases have distinct clinical manifestations and molecular pathogenesis. FXTAS is a late-adult-onset neurodegenerative disorder caused by a premutation (PM) allele (CGG expansion of 55–200 repeats), resulting in FMR1 gene hyperexpression. On the other hand, FXS is a neurodevelopmental disorder that results from a full mutation (FM) allele (CGG expansions of ≥200 repeats) leading to heterochromatization and transcriptional silencing of the FMR1 gene. The main challenge is to determine how CGG repeat expansion affects the fundamentally distinct nature of FMR1 expression in FM and PM ranges. Abnormal CGG repeat expansions form a variety of non-canonical DNA and RNA structures that can disrupt various cellular processes and cause distinct effects in PM and FM alleles. Here, we review these structures and how they are related to underlying mutations and disease pathology in FXS and FXTAS. Finally, as new CGG expansions within the genome have been identified, it will be interesting to determine their implications in disease pathology and treatment.

Enriched tandemly repeats in chromosomal fusion points of Rineloricaria latirostris (Boulenger, 1900) (Siluriformes: Loricariidae)

Cytogenetic data showed the enrichment of repetitive DNAs in chromosomal rearrangement points between closely related species in armored catfishes. Still, few studies integrated cytogenetic and genomic data aiming to identify their prone-to-break DNA sites. Here, we aimed to obtain the repetitive fraction in Rineloricaria latirostris to recognize the microsatellite and homopolymers flanking the regions previously described as chromosomal fusion points. The results indicated that repetitive DNAs in R. latirostris are predominantly DNA transposons, and considering the microsatellite and homopolymers, A/T-rich expansions were the most abundant. The in situ localization demonstrated the A/T-rich repetitive sequences are scattered on the chromosomes, while A/G-rich microsatellites units were accumulated in some regions. The DNA transposon hAT, the 5S rDNA, and 45S rDNA (previously identified in Robertsonian fusion points in R. latirostris) are clusterized with some microsatellites, especially (CA)n, (GA)n, and poly-A, which also are enriched in regions of chromosomal fusions. Our findings demonstrated that repetitive sequences such as rDNAs, hAT transposon, and microsatellite units flank probable evolutionary breakpoint regions in R. latirostris. However, due to the sequence unit homologies in different chromosomal sites, these repeat DNAs only may have facilitated chromosome fusion events in R. latirostris rather than work as a double-strand breakpoint site.

First record of the spatial organization of the nucleosome-less chromatin of dinoflagellates: The nonrandom distribution of microsatellites and bipolar arrangement of telomeres in the nucleus of Gambierdiscus australes (Dinophyceae)

Dinoflagellates are a group of protists whose exceptionally large genome is organized in permanently condensed nucleosome-less chromosomes. In this study, we examined the potential role of repetitive DNAs in both the structure of dinoflagellate chromosomes and the architecture of the dinoflagellate nucleus. Non-denaturing fluorescent in situ hybridization (ND-FSH) was used to determine the abundance and physical distribution of telomeric DNA and 16 microsatellites (1- to 4-bp repeats) in the nucleus of Gambierdiscus australes. The results showed an increased relative abundance of the different microsatellite motifs with increasing GC content. Two ND-FISH probes, (A)₂₀ and (AAT)₅ , did not yield signals whereas the remainder revealed a dispersed but nonrandom distribution of the microsatellites, mostly in clusters. The bean-shaped interphase nucleus of G. australes contained a region with a high density of trinucleotides. This nuclear compartment was located between the nucleolar organizer region (NOR), located on the concave side of the nucleus, and the convex side. Telomeric DNA was grouped in multiple foci and distributed in two polarized compartments: one associated with the NOR and the other peripherally located along the convex side of the nucleus. Changes in the position of the telomeres during cell division evidenced their dynamic distribution and thus that of the chromosomes during dinomitosis. These insights into the spatial organization of microsatellites and telomeres and thus into the nuclear architecture of G. australes will open up new lines of research into the structure and function of the nucleosome-less chromatin of dinoflagellates.

Utility of Circulating Cell-Free DNA in Assessing Microsatellite Instability and Loss of Heterozygosity in Breast Cancer Using Human Identification Approach

The diagnostic and prognostic utility of circulating cell-free DNA (cfDNA) in breast cancer (BC) patients was recently reported. Here, we investigated the use of cfDNA to examine microsatellite instability (MSI) and loss of heterozygosity (LOH) for early BC diagnosis. cfDNA and genomic DNA from 41 female BC patients and 40 healthy controls were quantified using NanoDrop spectrophotometry and real-time PCR. The stability of genomic and cfDNA was assessed using a high-resolution AmpFlSTR MiniFiler human identification kit. Significant increases in cfDNA plasma concentrations were observed in BC patients compared to controls. The genotype distribution of the eight autosomal short tandem repeat (STR) loci D7S820, D13S317, D21S11, D2S1338, D18S51, D16S539, FGA, and CSF1PO were in Hardy–Weinberg equilibrium. Significant differences in the allele frequencies of D7S820 allele-8, D21S11 allele-29, allele-30.2, allele-32.2, and CSF1PO allele-11 were seen between BC patients and controls. LOH and MSI were detected in 36.6% of the cfDNA of patients compared to genomic DNA. This study highlights the utility of plasma-derived cfDNA for earlier, less invasive, and cost-effective cancer diagnosis and molecular stratification. It also highlights the potential value of cfDNA in molecular profiling and biomarkers discovery in precision and forensic medicine.

Development of Disease-Resistance-Associated Microsatellite DNA Markers for Selective Breeding of Tilapia (Oreochromis spp.) Farmed in Taiwan

There are numerous means to improve the tilapia aquaculture industry, and one is to develop disease resistance through selective breeding using molecular markers. In this study, 11 disease-resistance-associated microsatellite markers including 3 markers linked to hamp2, 4 linked to hamp1, 1 linked to pgrn2, 2 linked to pgrn1, and 1 linked to piscidin 4 (TP4) genes were established for tilapia strains farmed in Taiwan after challenge with Streptococcus inae. The correlation analysis of genotypes and survival revealed a total of 55 genotypes related to survival by the chi-square and Z-test. Although fewer markers were found in B and N2 strains compared with A strain, they performed well in terms of disease resistance. It suggested that this may be due to the low potency of some genotypes and the combinatorial arrangement between them. Therefore, a predictive model was built by the genotypes of the parental generation and the mortality rate of different combinations was calculated. The results show the same trend of predicted mortality in the offspring of three new disease-resistant strains as in the challenge experiment. The present findings is a nonkilling method without requiring the selection by challenge with bacteria or viruses and might increase the possibility of utilization of selective breeding using SSR markers in farms.

Identifying biomarkers for prenatal diagnosis of neural tube defects based on "omics"

Neural tube defects (NTDs) are the most severe birth defects and the main cause of newborn death; posing a great challenge to the affected children, families, and societies. Presently, the clinical diagnosis of NTDs mainly relies on ultrasound images combined with certain indices, such as alpha-fetoprotein levels in the maternal serum and amniotic fluid. Recently, the discovery of additional biomarkers in maternal tissue has presented new possibilities for prenatal diagnosis. Over the past 20 years, "omics" techniques have provided the premise for the study of biomarkers. This review summarizes recent advances in candidate biomarkers for the prenatal diagnosis of fetal NTDs based on omics techniques using maternal biological specimens of different origins, including amniotic fluid, blood, and urine, which may provide a foundation for the early prenatal diagnosis of NTDs.

miRNA dysregulation is an emerging modulator of genomic instability

Genomic instability consists of a range of genetic alterations within the genome that contributes to tumor heterogeneity and drug resistance. It is a well-established characteristic of most cancer cells. Genome instability induction results from defects in DNA damage surveillance mechanisms, mitotic checkpoints and DNA repair machinery. Accumulation of genetic alterations ultimately sets cells towards malignant transformation. Recent studies suggest that miRNAs are key players in mediating genome instability. miRNAs are a class of small RNAs expressed in most somatic tissues and are part of the epigenome. Importantly, in many cancers, miRNA expression is dysregulated. Consequently, this review examines the role of miRNA dysregulation as a causal step for induction of genome instability and subsequent carcinogenesis. We focus specifically on mechanistic studies assessing miRNA(s) and specific subtypes of genome instability or known modes of genome instability. In addition, we provide insight on the existing knowledge gaps within the field and possible ways to address them.

Vaccines for Non-Viral Cancer Prevention

Cancer vaccines are a type of immune therapy that seeks to modulate the host’s immune system to induce durable and protective immune responses against cancer-related antigens. The little clinical success of therapeutic cancer vaccines is generally attributed to the immunosuppressive tumor microenvironment at late-stage diseases. The administration of cancer-preventive vaccination at early stages, such as pre-malignant lesions or even in healthy individuals at high cancer risk could increase clinical efficacy by potentiating immune surveillance and pre-existing specific immune responses, thus eliminating de novo appearing lesions or maintaining equilibrium. Indeed, research focus has begun to shift to these approaches and some of them are yielding encouraging outcomes.

Genome-wide development and application of miRNA-SSR markers in Melilotus genus

Genetic diversity of plants is the brace of biodiversity and diversity within species, between species, and of ecosystems. SSR markers are the most preferable molecular marker tool that has been successfully used to study the genetic diversity of plant species. Development of miRNA-SSR markers has been deed in animals but is still limited in plants. In this study, 365 precursors miRNA were extracted from Melilotus albus (Ma) genome and used to design Ma miRNA-SSR primers. 137 Ma primer pairs (79 from known and 58 from novel pre-miRNAs) were obtained. 66 pairs of Ma miRNA-SSR primers were selected with polymorphisms and expected fragment size. The polymorphisms of primers were evaluated in 60 individuals of 15 Ma accessions. A total of 66 primer pairs showed high polymorphism, with average polymorphic information content of 0.49 among 15 Ma accessions and 0.63 among 18 Melilotus species, indicating that these primers have high polymorphisms. The number of alleles produced per primer ranged from 2 to 6 with an average of 3.6 alleles per locus in Ma accessions, and 2 to 10 numbers of alleles with a mean of 5.24 alleles per locus in Melilotus spp. For further studies, the genetic relationship was examined and the cluster analysis showed that 15 Ma accessions were grouped in three groups, on the other hand, 18 Melilotus species clustered into two groups. The analysis of molecular variance (AMOVA) revealed that 64.82% of the variation was found within the species and 35.18% between the species. The population structure analysis showed similar results with PCA analysis in that 18 species were grouped in two groups. In addition, 16,450 miRNA target genes were identified and used for GO and KEGG analysis. This is the first study to develop miRNA-SSR molecular markers in Melilotus spp., which has a great potential for marker-assisted, genetic improvement, genotyping applications, QTL analysis, and molecular-assisted selection studies for plant breeders and other researchers.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s12298-021-01086-z.

The Simple Biology of Flipons and Condensates Enhances the Evolution of Complexity

The classical genetic code maps nucleotide triplets to amino acids. The associated sequence composition is complex, representing many elaborations during evolution of form and function. Other genomic elements code for the expression and processing of RNA transcripts. However, over 50% of the human genome consists of widely dispersed repetitive sequences. Among these are simple sequence repeats (SSRs), representing a class of flipons, that under physiological conditions, form alternative nucleic acid conformations such as Z-DNA, G4 quartets, I-motifs, and triplexes. Proteins that bind in a structure-specific manner enable the seeding of condensates with the potential to regulate a wide range of biological processes. SSRs also encode the low complexity peptide repeats to patch condensates together, increasing the number of combinations possible. In situations where SSRs are transcribed, SSR-specific, single-stranded binding proteins may further impact condensate formation. Jointly, flipons and patches speed evolution by enhancing the functionality of condensates. Here, the focus is on the selection of SSR flipons and peptide patches that solve for survival under a wide range of environmental contexts, generating complexity with simple parts.

Predicting stability of DNA bulge at mononucleotide microsatellite

Mononucleotide microsatellites are clinically and forensically crucial DNA sequences due to their high mutability and abundance in the human genome. As a mutagenic intermediate of an indel in a microsatellite and a consequence of probe hybridization after such mutagenesis, a bulge with structural degeneracy sliding within a microsatellite is formed. Stability of such dynamic bulges, however, is still poorly understood despite their critical role in cancer genomics and neurological disease studies. In this paper, we have built a model that predicts the thermodynamics of a sliding bulge at a microsatellite. We first identified 40 common bulge states that can be assembled into any sliding bulges, and then characterized them with toehold exchange energy measurement and the partition function. Our model, which is the first to predict the free energy of sliding bulges with more than three repeats, can infer the stability penalty of a sliding bulge of any sequence and length with a median prediction error of 0.22 kcal/mol. Patterns from the prediction clearly explain landscapes of microsatellites observed in the literature, such as higher mutation rates of longer microsatellites and C/G microsatellites.

Morphometric study of encephalic lesions in aborted bovine fetuses naturally infected by two subpopulations of Neospora caninum

Neospora caninum is a major reproductive disease in cattle worldwide. In the Argentinian Humid Pampa, the seroprevalence, incidence of abortions, and economic losses due to neosporosis are considerably higher in dairy than in beef cattle. Despite this, we recently demonstrated that N. caninum subpopulations are indistinctly distributed in both dairy and beef production systems. The association between genotypic characteristics defined by microsatellite analysis and the virulence of the different strains-particularly with regard to the severity and extension of histological lesions-is largely unknown. Herein, we used a morphometric approach to analyze encephalic lesions in 62 bovine fetuses spontaneously infected by N. caninum. Morphometric parameters (average size of focal lesions, number of foci/cm² and the percentage of the section affected by lesions) were compared according to the N. caninum subpopulations found in our previous microsatellite genotyping analysis, animal biotype (beef versus dairy), and fetal age (second stage of gestation versus third stage). The average size of the lesions differed significantly among fetuses with different gestational ages; however, no significant differences among animal biotypes or genotypic patterns were found. Further research into the genetic, molecular, and husbandry factors that could account for this greater impact in Argentinian dairy herds is needed.

Discovery of widespread transcription initiation at microsatellites predictable by sequence-based deep neural network

Using the Cap Analysis of Gene Expression (CAGE) technology, the FANTOM5 consortium provided one of the most comprehensive maps of transcription start sites (TSSs) in several species. Strikingly, ~72% of them could not be assigned to a specific gene and initiate at unconventional regions, outside promoters or enhancers. Here, we probe these unassigned TSSs and show that, in all species studied, a significant fraction of CAGE peaks initiate at microsatellites, also called short tandem repeats (STRs). To confirm this transcription, we develop Cap Trap RNA-seq, a technology which combines cap trapping and long read MinION sequencing. We train sequence-based deep learning models able to predict CAGE signal at STRs with high accuracy. These models unveil the importance of STR surrounding sequences not only to distinguish STR classes, but also to predict the level of transcription initiation. Importantly, genetic variants linked to human diseases are preferentially found at STRs with high transcription initiation level, supporting the biological and clinical relevance of transcription initiation at STRs. Together, our results extend the repertoire of non-coding transcription associated with DNA tandem repeats and complexify STR polymorphism.

STRs: Ancient Architectures of the Genome beyond the Sequence

Short tandem repeats (STRs) are commonly defined as short runs of repetitive nucleotides, consisting of tandemly repeating 2-6- bp motif units, which are ubiquitously distributed throughout genomes. Functional STRs are polymorphic in the population, and their variations influence gene expression, which subsequently may result in pathogenic phenotypes. To understand STR phenotypic effects and their functional roles, we describe four different mutational mechanisms including the unequal crossing-over model, gene conversion, retrotransposition mechanism and replication slippage. Due to the multi-allelic nature, small length, abundance, high variability, codominant inheritance, nearly neutral evolution, extensive genome coverage and simple assaying of STRs, these markers are widely used in various types of biological research, including population genetics studies, genome mapping, molecular epidemiology, paternity analysis and gene flow studies. In this review, we focus on the current knowledge regarding STR genomic distribution, function, mutation and applications.

Microsatellites as Agents of Adaptive Change: An RNA-Seq-Based Comparative Study of Transcriptomes from Five Helianthus Species

Mutations that provide environment-dependent selective advantages drive adaptive divergence among species. Many phenotypic differences among related species are more likely to result from gene expression divergence rather than from non-synonymous mutations. In this regard, cis-regulatory mutations play an important part in generating functionally significant variation. Some proposed mechanisms that explore the role of cis-regulatory mutations in gene expression divergence involve microsatellites. Microsatellites exhibit high mutation rates achieved through symmetric or asymmetric mutation processes and are abundant in both coding and non-coding regions in positions that could influence gene function and products. Here we tested the hypothesis that microsatellites contribute to gene expression divergence among species with 50 individuals from five closely related Helianthus species using an RNA-seq approach. Differential expression analyses of the transcriptomes revealed that genes containing microsatellites in non-coding regions (UTRs and introns) are more likely to be differentially expressed among species when compared to genes with microsatellites in the coding regions and transcripts lacking microsatellites. We detected a greater proportion of shared microsatellites in 5′UTRs and coding regions compared to 3′UTRs and non-coding transcripts among Helianthus spp. Furthermore, allele frequency differences measured by pairwise FST at single nucleotide polymorphisms (SNPs), indicate greater genetic divergence in transcripts containing microsatellites compared to those lacking microsatellites. A gene ontology (GO) analysis revealed that microsatellite-containing differentially expressed genes are significantly enriched for GO terms associated with regulation of transcription and transcription factor activity. Collectively, our study provides compelling evidence to support the role of microsatellites in gene expression divergence.

Mismatch repair-deficient hormone receptor-positive breast cancers: Biology and pathological characterization

The clinical outcome of patients with a diagnosis of hormone receptor (HR)+ breast cancer has improved remarkably since the arrival of endocrine therapy. Yet, resistance to standard treatments is a major clinical challenge for breast cancer specialists and a life-threatening condition for the patients. In breast cancer, mismatch repair (MMR) status assessment has been demonstrated to be clinically relevant not only in terms of screening for inherited conditions such as Lynch syndrome, but also for prognostication, selection for immunotherapy, and early identification of therapy resistance. Peculiar traits characterize the MMR biology in HR+ breast cancers compared to other cancer types. In these tumors, MMR genetic alterations are relatively rare, occurring in ~3 % of cases. On the other hand, modifications at the protein level can be observed also in the absence of gene alterations and vice versa. In HR+ breast cancers, the prognostic role of MMR deficiency has been confirmed by several studies, but its predictive value remains a matter of controversy. The characterization of MMR status in these patients is troubled by the lack of tumor-specific guidelines and/or companion diagnostic tests. For this reason, precise identification of MMR-deficient breast cancers can be problematic. A deeper understanding of the MMR biology and clinical actionability in HR+ breast cancer may light the path to effective tumor-specific diagnostic tools. For a precise MMR status profiling, the specific strengths and limitations of the available technologies should be taken into consideration. This article aims at providing a comprehensive overview of the current state of knowledge of MMR alterations in HR+ breast cancer. The available armamentarium for MMR testing in these tumors is also examined along with possible strategies for a tailored pathological characterization.

Sequence-dependent nucleosome formation in trinucleotide repeats evaluated by in vivo chemical mapping

Trinucleotide repeat sequences (TRSs), consisting of 10 unique classes of repeats in DNA, are members of microsatellites and abundantly and non-randomly distributed in many eukaryotic genomes. The lengths of TRSs are mutable, and the expansions of several TRSs are implicated in hereditary neurological diseases. However, the underlying causes of the biased distribution and the dynamic properties of TRSs in the genome remain elusive. Here, we examined the effects of TRSs on nucleosome formation in vivo by histone H4-S47C site-directed chemical cleavages, using well-defined yeast minichromosomes in which each of the ten TRS classes resided in the central region of a positioned nucleosome. We showed that (AAT)₁₂ and (ACT)₁₂ act as strong nucleosome-promoting sequences, while (AGG)₁₂ and (CCG)₁₂ act as nucleosome-excluding sequences in vivo. The local histone binding affinity scores support the idea that nucleosome formation in TRSs, except for (AGG)₁₂, is mainly determined by the affinity for the histone octamers. Overall, our study presents a framework for understanding the nucleosome-forming abilities of TRSs.

Comparison of the Microsatellite Distribution Patterns in the Genomes of Euarchontoglires at the Taxonomic Level

Microsatellite or simple sequence repeat (SSR) instability within genes can induce genetic variation. The SSR signatures remain largely unknown in different clades within Euarchontoglires, one of the most successful mammalian radiations. Here, we conducted a genome-wide characterization of microsatellite distribution patterns at different taxonomic levels in 153 Euarchontoglires genomes. Our results showed that the abundance and density of the SSRs were significantly positively correlated with primate genome size, but no significant relationship with the genome size of rodents was found. Furthermore, a higher level of complexity for perfect SSR (P-SSR) attributes was observed in rodents than in primates. The most frequent type of P-SSR was the mononucleotide P-SSR in the genomes of primates, tree shrews, and colugos, while mononucleotide or dinucleotide motif types were dominant in the genomes of rodents and lagomorphs. Furthermore, (A)n was the most abundant motif in primate genomes, but (A)n, (AC)n, or (AG)n was the most abundant motif in rodent genomes which even varied within the same genus. The GC content and the repeat copy numbers of P-SSRs varied in different species when compared at different taxonomic levels, reflecting underlying differences in SSR mutation processes. Notably, the CDSs containing P-SSRs were categorized by functions and pathways using Gene Ontology and Kyoto Encyclopedia of Genes and Genomes annotations, highlighting their roles in transcription regulation. Generally, this work will aid future studies of the functional roles of the taxonomic features of microsatellites during the evolution of mammals in Euarchontoglires.

Spatial distance between sites of sampling associated with genetic variation among Neospora caninum in aborted bovine foetuses from northern Italy

BACKGROUND

Neospora caninum, a coccidian protozoan, represents an important cause of bovine abortion. Available N. caninum strains show considerable variation in vitro and in vivo, including different virulence in cattle. To which extent sexual recombination, which is possible in the intestines of domestic dogs and closely related carnivores as definitive hosts, contributes to this variation is not clear yet.

METHODS

Aborted bovine foetuses were collected between 2015 and early 2019 from Italian Holstein Friesian dairy herds suffering from reproductive problems. A total of 198 samples were collected from 165 intensive farms located in Lombardy, northern Italy. N. caninum samples were subjected to multilocus-microsatellite genotyping using ten previously established microsatellite markers. In addition to our own data, those from a recent study providing data on five markers from other northern Italian regions were included and analysed.

RESULTS

Of the 55 samples finally subjected to genotyping, 35 were typed at all or 9 out of 10 loci and their individual multilocus-microsatellite genotype (MLMG) determined. Linear regression revealed a statistically significant association between the spatial distance of the sampling sites with the genetic distance of N. caninum MLMGs (P < 0.001). Including data from this and a previous North Italian study into eBURST analysis revealed that several of N. caninum MLMGs from northern Italy separate into four groups; most of the samples from Lombardy clustered in one of these groups. Principle component analysis revealed similar clusters and confirmed MLMG groups identified by eBURST. Variations observed between MLMGs were not equally distributed over all loci, but predominantly observed in MS7, MS6A, or MS10.

CONCLUSIONS

Our findings confirm the concept of local N. caninum subpopulations. The geographic distance of sampling was associated with the genetic distance as determined by microsatellite typing. Results suggest that multi-parental recombination in N. caninum is a rare event, but does not exclude uniparental mating. More comprehensive studies on microsatellites in N. caninum and related species like Toxoplasma gondii should be undertaken, not only to improve genotyping capabilities, but also to understand possible functions of these regions in the genomes of these parasites.

Short tandem repeat near hypoxia response element (HRE) instead of HRE genetic variants in promoter calcitonin receptor-like receptor (CRLR) gene as risk factor in severe preeclampsia: a preliminary study

Objective

Calcitonin receptor-like receptor (CRLR) regulates vasoconstriction and dilatation; the expression increases during hypoxia via activation of hypoxia response element (HRE) in CRLR gene promoter region. Variant in HRE, as well short tandem repeat (STR) variants near HRE in CRLR alters the gene expression. This study focused on a case–control study to investigate the expression of genetic typing CLRL promoter variant in pregnant women with severe preeclampsia and normal pregnancies, we also tried to describe interesting findings of the genetic expression in anemic patients in the severe preeclampsia group. Our aimed to observe the correlation of CRLR gene promoter variant and anemia in severe preeclampsia.

Results

There was no nucleotide variant in HRE; CACA box prior to HRE varied in length (15–24); CACA box with length > 20 was used as cut off point. Hb was lower in CACA box length ≥ 21 (10.33 ± 1.57) vs. < 21 (11.01 ± 1.67; p = 0.391). CACA box polymorphism and anemia were correlated in severe preeclampsia (p = 0.005) OR 0.038 (CI 0.003–0.544); not in normal (p = 0.069).

Associations of BCL2 CA-Repeat Polymorphism and Breast Cancer Susceptibility in Isfahan Province of Iran

BCL2 apoptosis regulator (BCL2) is a cause of tumorigenesis whose CA-repeat promoter polymorphisms has inconsistent association with various types of cancers. The association of BCL2 polymorphism with breast cancer was investigated in the Isfahan province of Iran. PCRamplification of the CA-repeat was followed by polyacrylamide gel electrophoresis and direct sequencing for 120 breast cancer women and an equal number of corresponding healthy control individuals. Seven different alleles, ranging from 11 to 17 CA-repeats were observed. Short alleles with 11 to 14 repeats were protective (OR 0.363, P = 0.001), but large alleles with 15 to 17 repeats were threatening against breast cancer development (OR 2.780, P = 0.001). Accordingly, genotypes with large alleles showed a higher risk of breast cancer development (OR 3.400, P = 0.004). ERS1\ERBB2 positive breast cancer patients, but not PGRpositive ones, showed protection against breast cancer (OR 0.405, OR 0.346 respectively). In conclusion, women with at least one large allele of BCL2 were 3.4 times at higher risk of breast cancer development in the Isfahan province of Iran.

Comparison of microsatellite distribution patterns in twenty-nine beetle genomes

Simple sequence repeats (SSRs) represent an important source of genetic variation that provides a basis for adaptation to different environments in organisms. In this study, we examined the distribution patterns of SSRs in twenty-nine beetle genomes and carried out Gene Ontology (GO) analysis of CDSs embedded with perfect SSRs (P-SSRs). The results demonstrated that imperfect SSRs (I-SSRs) represented the most abundant SSR category in beetle genomes and in different genomic regions (CDS, exon, and intron regions). The numbers of P-SSRs, I-SSRs, compound SSRs, and variable number tandem repeats were positively correlated with beetle genome size, whereas neither the frequency nor the density of the SSRs was correlated with genome size. Moreover, our results demonstrated that common genomic features of P-SSRs within the same suborder or family of Coleoptera were rare. Mono-, di-, tri-, or tetranucleotide SSRs were the most abundant P-SSR categories in beetle genomes. The preferred predominant repeat motif among the mononucleotide P-SSRs was (A)n, but the most frequent repeat motifs for other length classes varied differentially among these genomes. Furthermore, the P-SSR type with the highest GC content differed in the beetle genomes and in different genomic regions. CV (coefficient of variability) analysis demonstrated that the repeat copy numbers of P-SSRs presented relatively higher variation in introns than in CDSs and exons. The GO terms of CDSs containing P-SSRs for molecular functions were mainly enriched in "binding" and "transcription". Our findings will be useful for studying the functional roles of microsatellite heterogeneity in beetle adaptation.

DNA methylation in satellite repeats disorders

Despite the tremendous progress made in recent years in assembling the human genome, tandemly repeated DNA elements remain poorly characterized. These sequences account for the vast majority of methylated sites in the human genome and their methylated state is necessary for this repetitive DNA to function properly and to maintain genome integrity. Furthermore, recent advances highlight the emerging role of these sequences in regulating the functions of the human genome and its variability during evolution, among individuals, or in disease susceptibility. In addition, a number of inherited rare diseases are directly linked to the alteration of some of these repetitive DNA sequences, either through changes in the organization or size of the tandem repeat arrays or through mutations in genes encoding chromatin modifiers involved in the epigenetic regulation of these elements. Although largely overlooked so far in the functional annotation of the human genome, satellite elements play key roles in its architectural and topological organization. This includes functions as boundary elements delimitating functional domains or assembly of repressive nuclear compartments, with local or distal impact on gene expression. Thus, the consideration of satellite repeats organization and their associated epigenetic landmarks, including DNA methylation (DNAme), will become unavoidable in the near future to fully decipher human phenotypes and associated diseases.

A DNA G-quadruplex/i-motif hybrid

DNA can form many structures beyond the canonical Watson–Crick double helix. It is now clear that noncanonical structures are present in genomic DNA and have biological functions. G-rich G-quadruplexes and C-rich i-motifs are the most well-characterized noncanonical DNA motifs that have been detected in vivo with either proscribed or postulated biological roles. Because of their independent sequence requirements, these structures have largely been considered distinct types of quadruplexes. Here, we describe the crystal structure of the DNA oligonucleotide, d(CCAGGCTGCAA), that self-associates to form a quadruplex structure containing two central antiparallel G-tetrads and six i-motif C–C⁺ base pairs. Solution studies suggest a robust structural motif capable of assembling as a tetramer of individual strands or as a dimer when composed of tandem repeats. This hybrid structure highlights the growing structural diversity of DNA and suggests that biological systems may harbor many functionally important non-duplex structures.

SSRome: an integrated database and pipelines for exploring microsatellites in all organisms

Over the past decade, many databases focusing on microsatellite mining on a genomic scale were released online with at least one of the following major deficiencies: (i) lacking the classification of microsatellites as genic or non-genic, (ii) not comparing microsatellite motifs at both genic and non-genic levels in order to identify unique motifs for each class or (iii) missing SSR marker development. In this study, we have developed ‘SSRome’ as a web-based, user-friendly, comprehensive and dynamic database with pipelines for exploring microsatellites in 6533 organisms. In the SSRome database, 158 million microsatellite motifs are identified across all taxa, in addition to all the mitochondrial and chloroplast genomes and expressed sequence tags available from NCBI. Moreover, 45.1 million microsatellite markers were developed and classified as genic or non-genic. All the stored motif and marker datasets can be downloaded freely. In addition, SSRome provides three user-friendly tools to identify, classify and compare motifs on either a genome- or transcriptome-wide scale. With the implementation of PHP, HTML and JavaScript, users can upload their data for analysis via a user-friendly GUI. SSRome represents a powerful database and mega-tool that will assist researchers in developing and dissecting microsatellite markers on a high-throughput scale.