The mechanism of transactivation regulation due to polymorphic short tandem repeats (STRs) using IGF1 promoter as a model

The role of tandem repeat expansions in brain disorders

The human genome contains numerous genetic polymorphisms contributing to different health and disease outcomes. Tandem repeat (TR) loci are highly polymorphic yet under-investigated in large genomic studies, which has prompted research efforts to identify novel variations and gain a deeper understanding of their role in human biology and disease outcomes. We summarize the current understanding of TRs and their implications for human health and disease, including an overview of the challenges encountered when conducting TR analyses and potential solutions to overcome these challenges. By shedding light on these issues, this article aims to contribute to a better understanding of the impact of TRs on the development of new disease treatments.

Genetic characteristics of spouse selection based on short tandem repeats in DNA and lunula count on fingertip

OBJECTIVE

The aim of this study was to assess the correlation of spouse selection with short tandem repeats (STRs) in DNA and with the number of fingertip lunulae to investigate the role of heredity in spouse selection.

METHODS

We randomly selected a total of 286 couples (husband and wife) as a couple group while 200 paired subjects (a man randomly matched with a woman as a pair of subjects) were selected as a non-spouse group for DNA typing, and to investigate lunulae in spouse selection, a total of 554 couples were selected as a couple group and 500 pairs of subjects were selected as a control group.

RESULTS

A significant difference of STR matching number (a large value implies a higher genetic similarity) between spouse group and non-spouse group were observed (12.3 ± 2.7 vs. 11.8 ± 2.6; p < 0.05). A significant difference of the lunula matching number (difference of lunula counts between a paired subjects, a lower value implies a higher genetic similarity) between two groups were also observed for the lunula counts (1.55 ± 1.88 vs. 3.53 ± 2.40; p < 0.01).

CONCLUSION

Significant and unprecedented relationships were found between the couples and polymorphic STRs, and between spouse selection and lunula counts. Polymorphic STRs and fingertip lunulae counts provide an initial insight into the potentially important contributions that genetic characteristics may play a key role in spouse selection.

Chromatin analysis of adult pluripotent stem cells reveals a unique stemness maintenance strategy

Many highly regenerative organisms maintain adult pluripotent stem cells throughout their life, but how the long-term maintenance of pluripotency is accomplished is unclear. To decipher the regulatory logic of adult pluripotent stem cells, we analyzed the chromatin organization of stem cell genes in the planarian Schmidtea mediterranea. We identify a special chromatin state of stem cell genes, which is distinct from that of tissue-specific genes and resembles constitutive genes. Where tissue-specific promoters have detectable transcription factor binding sites, the promoters of stem cell-specific genes instead have sequence features that broadly decrease nucleosome binding affinity. This genic organization makes pluripotency-related gene expression the default state in these cells, which is maintained by the activity of chromatin remodelers ISWI and SNF2 in the stem cells.

A Poly(dA:dT) Tract in the IGF1 Gene Is a Genetic Marker for Growth Traits in Pigs

Insulin-like growth factor 1 (IGF1) is an important regulator of body growth, development, and metabolism. The poly(dA:dT) tract affects the accessibility of transcription factor binding sites to regulate transcription. Therefore, this study assessed the effects of two poly(dA:dT) tracts on the transcriptional activity of porcine IGF1. The luciferase assay results demonstrated that the poly(dA:dT) tract 2 (−264/−255) was a positive regulatory element for IGF1 gene expression, and the activities between the different lengths of the poly(dA:dT) tract 2 were significant (p<0.01). The transcription factor C/EBPα inhibited the transcription of IGF1 by binding to tract 2, and the expression levels between the lengths of tract 2 after C/EBPα binding were also statistically different (p<0.01). Only the alleles 10T and 11T were found in the tract 2 in commercial pig breeds, while the 9T, 10T, and 11T alleles were found in Chinese native pig breeds. The allele frequencies were in Hardy−Weinberg equilibrium in all pig breeds. The genotypes of tract 2 were significantly associated with the growth traits (days to 115 kg and average daily gain) (p<0.05) in commercial pig breeds. Based on these findings, it can be concluded that the tract 2 mutation could be applied as a candidate genetic marker for growth trait selection in pig breeding programs.

The Impact of Leukemia on the Detection of Short Tandem Repeat (STR) Markers

INTRODUCTION

Short tandem repeats (STRs) have been used for various identity typing methods worldwide. They have high discrimination power in human identification in forensics, paternity testing, missed personal identification, genetic diseases, and gene regulatory functions. They have also been used to detect and monitor the stability of diseases, including various types of cancer. This study aimed to investigate the impact of leukemia on the detection and stability of STR markers.

METHODS

DNA was isolated from 30 participants (15 with chronic myeloid leukemia( CML) and 15 healthy controls) and used to amplify STR markers using specific primers.

RESULTS

We found that the blood of those with leukemia had more 9.3 and 9 alleles at the tyrosine hydroxylase 1 (TH01) marker than the blood of the healthy control samples. The results of this study will help researchers understand leukemia's effect on the detection and stability of STR markers in leukemic patients compared to healthy individuals.

CONCLUSION

Our results demonstrate that STR markers could become useful in genetic studies of leukemia cases.

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.

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.

Genome-Wide Search for SNP Interactions in GWAS Data: Algorithm, Feasibility, Replication Using Schizophrenia Datasets

In this study, we looked for potential gene-gene interaction in susceptibility to schizophrenia by an exhaustive searching for SNP-SNP interactions in 3 GWAS datasets (phs000021:phg000013, phs000021:phg000014, phs000167) using our recently published algorithm. The search space for SNP-SNP interaction was confined to 8 biologically plausible ways of interaction under dominant-dominant or recessive-recessive modes. First, we performed our search of all pair-wise combination of 729,454 SNPs after filtering by SNP genotype quality. All possible pairwise interactions of any 2 SNPs (5 × 10¹¹) were exhausted to search for significant interaction which was defined by p-value of chi-square tests. Nine out the top 10 interactions, protein coding genes were partnered with non-coding RNA (ncRNA) which suggested a new alternative insight into interaction biology other than the frequently sought-after protein-protein interaction. Therefore, we extended to look for replication among the top 10,000 interaction SNP pairs and high proportion of concurrent genes forming the interaction pairs were found. The results indicated that an enrichment of signals over noise was present in the top 10,000 interactions. Then, replications of SNP-SNP interaction were confirmed for 14 SNPs-pairs in both replication datasets. Biological insight was highlighted by a potential binding between FHIT (protein coding gene) and LINC00969 (lncRNA) which showed a replicable interaction between their SNPs. Both of them were reported to have expression in brain. Our study represented an early attempt of exhaustive interaction analysis of GWAS data which also yield replicated interaction and new insight into understanding of genetic interaction in schizophrenia.

Forensic Autosomal Short Tandem Repeats and Their Potential Association With Phenotype

Forensic DNA profiling utilizes autosomal short tandem repeat (STR) markers to establish identity of missing persons, confirm familial relations, and link persons of interest to crime scenes. It is a widely accepted notion that genetic markers used in forensic applications are not predictive of phenotype. At present, there has been no demonstration of forensic STR variants directly causing or predicting disease. Such a demonstration would have many legal and ethical implications. For example, is there a duty to inform a DNA donor if a medical condition is discovered during routine analysis of their sample? In this review, we evaluate the possibility that forensic STRs could provide information beyond mere identity. An extensive search of the literature returned 107 articles associating a forensic STR with a trait. A total of 57 of these studies met our inclusion criteria: a reported link between a STR-inclusive gene and a phenotype and a statistical analysis reporting a p-value less than 0.05. A total of 50 unique traits were associated with the 24 markers included in the 57 studies. TH01 had the greatest number of associations with 27 traits reportedly linked to 40 different genotypes. Five of the articles associated TH01 with schizophrenia. None of the associations found were independently causative or predictive of disease. Regardless, the likelihood of identifying significant associations is increasing as the function of non-coding STRs in gene expression is steadily revealed. It is recommended that regular reviews take place in order to remain aware of future studies that identify a functional role for any forensic STRs.

Sex-specific effects of a microsatellite polymorphism on human growth hormone receptor gene expression

Growth hormone (GH) binds to its specific receptor (GHR) at the surface of target cells activating multiple signaling pathways implicated in growth and metabolism. Dysregulation of GHRs leads to pathophysiological states that most commonly affect stature. We previously showed the association of a polymorphic (n = 15-37) GT microsatellite in the human GHR gene promoter with short stature in a sex-specific manner. In the present study we evaluated the functional relevance of this polymorphism in regulating GHR expression. Using luciferase reporter assays, we found that the GT repeat had a significant cis regulatory effect in response to HIF1α and a potential repressor role following C/EBPβ stimulation. Using a digital PCR application to measure allelic imbalance (AI), we showed a high prevalence of AI (∼76%) at the GHR locus in lymphoblastoid cell lines (LCLs), with a significantly higher degree of imbalance in LCLs derived from males. Examination of expression of GHR as well as other members of the GH-IGF1 axis in the LCLs revealed significant associations of GHR, IGF1 and BCL2 expression with GT genotype in a sex-specific manner. Our results suggest that this GT microsatellite exerts both cis and trans effects in a sex-specific context, revealing a new mechanism by which GHR gene expression is regulated.

Regulatory Architecture of the Neuronal Cacng2/Tarpγ2 Gene Promoter: Multiple Repressive Domains, a Polymorphic Regulatory Short Tandem Repeat, and Bidirectional Organization with Co-regulated lncRNAs

CACNG2 (TARPγ2, Stargazin) is a multi-functional regulator of excitatory neurotransmission and has been implicated in the pathological processes of several brain diseases. Cacng2 function is dependent upon expression level, but currently, little is known about the molecular mechanisms that control expression of this gene. To address this deficit and investigate disease-related gene variants, we have cloned and characterized the rat Cacng2 promoter and have defined three major features: (i) multiple repressive domains that include an array of RE-1 silencing transcription factor (REST) elements, and a calcium regulatory element-binding factor (CaRF) element, (ii) a (poly-GA) short tandem repeat (STR), and (iii) bidirectional organization with expressed lncRNAs. Functional activity of the promoter was demonstrated in transfected neuronal cell lines (HT22 and PC12), but although selective removal of REST and CaRF domains was shown to enhance promoter-driven transcription, the enhanced Cacng2 promoter constructs were still about fivefold weaker than a comparable rat Synapsin-1 promoter sequence. Direct evidence of REST activity at the Cacng2 promoter was obtained through co-transfection with an established dominant-negative REST (DNR) construct. Investigation of the GA-repeat STR revealed polymorphism across both animal strains and species, and size variation was also observed in absence epilepsy disease model cohorts (Genetic Absence Epilepsy Rats, Strasbourg [GAERS] and non-epileptic control [NEC] rats). These data provide evidence of a genotype (STR)-phenotype correlation that may be unique with respect to proximal gene regulatory sequence in the demonstrated absence of other promoter, or 3' UTR variants in GAERS rats. However, although transcriptional regulatory activity of the STR was demonstrated in further transfection studies, we did not find a GAERS vs. NEC difference, indicating that this specific STR length variation may only be relevant in the context of other (Cacna1h and Kcnk9) gene variants in this disease model. Additional studies revealed further (bidirectional) complexity at the Cacng2 promoter, and we identified novel, co-regulated, antisense rat lncRNAs that are paired with Cacng2 mRNA. These studies have provided novel insights into the organization of a synaptic protein gene promoter, describing multiple repressive and modulatory domains that can mediate diverse regulatory inputs.

Relationship of SNP rs35767 in IGF-1 promoter region with susceptibility to colorectal cancer

In vitro and animal experiments demonstrate that IGF-1 appears to play a role in the development and growth of colorectal cancer and the function of free IGF-1 protein is mediated by IGF-1R. The IGF-1R system plays a critical role in promoting the normal development of cells and malignant transformation via the phosphatidylinositol 3-kinase (PI3)/AKTA and mitogen-activated protein kinase (MAPK) pathways. Different variants of the promoter of IGF-1 are involved in the risk of suffering from various diseases. The current study examined the relationship between IGF-1 rs35767 polymorphism and the risk of colorectal cancer (CRC) in a population from China. The genotypes of rs35767 polymorphism of the promoter region of IGF-1 were examined in 734 subjects: 367 patients with CRC and 367 healthy individuals by PCR. LDL and TC levels in colorectal cancer patients were significantly higher than those in the healthy control group (P = 0.045 and 0.046, respectively). Compared with CC genotype carriers, people with the CT genotype had a 1.39-fold higher risk of CRC (OR = 1.399, 95% CI 1.029-1.901 P = 0.032). There was no association between genotypes of rs35767 and the risk of CRC, after stratification according to gender. The patients who carried the T allele tend to have poor tissue differentiation. SNP rs35767 polymorphism associated with IGF-1 levels may be associated with susceptibility to colorectal cancer. People with the CT genotype may have a higher risk of CRC, and the patients who carried T allele tend to have poor tissue differentiation.

Functional Mechanisms of Microsatellite DNA in Eukaryotic Genomes

Microsatellite repeat DNA is best known for its length mutability, which is implicated in several neurological diseases and cancers, and often exploited as a genetic marker. Less well-known is the body of work exploring the widespread and surprisingly diverse functional roles of microsatellites. Recently, emerging evidence includes the finding that normal microsatellite polymorphism contributes substantially to the heritability of human gene expression on a genome-wide scale, calling attention to the task of elucidating the mechanisms involved. At present, these are underexplored, but several themes have emerged. I review evidence demonstrating roles for microsatellites in modulation of transcription factor binding, spacing between promoter elements, enhancers, cytosine methylation, alternative splicing, mRNA stability, selection of transcription start and termination sites, unusual structural conformations, nucleosome positioning and modification, higher order chromatin structure, noncoding RNA, and meiotic recombination hot spots.

Association of a Cac8I polymorphism in the IGF1 gene with growth traits in Indian goats

The Insulin-like Growth Factor 1 (IGF1) gene is a member of somatotropic axis and plays a key role in proliferation of cells, mitosis, myogenesis, meiosis, differentiation in foetal development and post natal growth. The objectives of this study were to verify the single nucleotide polymorphisms (SNPs) in IGF1 gene and their association with growth traits in two indigenous native goat genetic groups of Kerala, viz., Malabari and Attappady Black. A total of 277 goats were genotyped using a polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) using the restriction enzyme Cac8I. One SNP, A224G was detected in the 5′ non-coding region of the IGF1 gene, and accordingly two genotypes were revealed, GG and AG. This SNP was significantly associated with growth traits in Attappady Black goats, which is maintained as meat breed in Kerala. Results from this study demonstrated higher performance of GG animals for growth traits. The association of IGF1 gene with these traits emphasizes the importance of caprine IGF1 as a candidate gene for growth traits in goat breeding.