Mono-nucleotide repeats (MNRs): a neglected polymorphism for generating high density genetic maps in silico

Targeting Multiple Tumors Using T-Cells Engineered to Express a Natural Cytotoxicity Receptor 2-Based Chimeric Receptor

Recent developments in cancer treatment are demonstrating the increasing and powerful potential of immunotherapeutic strategies. In this regard, the adoptive transfer of tumor-specific T-lymphocytes approaches can lead to tumor regression in cancer patients. More recently, the use of T-cells genetically engineered to express cancer-specific receptors such as the anti-CD19 chimeric antigen receptor (CAR) continues to show promise for the treatment of hematological malignancies. Still, there is a crucial need to develop efficient CAR-T cell approaches for the treatment of solid tumors. It has been shown that other lymphocytes such as natural killer (NK) cells can demonstrate potent antitumor function—nonetheless, their use in immunotherapy is rather limited due to difficulties in expanding these cells to therapeutically relevant numbers and to suppression by endogenous inhibitory mechanisms. Cancer recognition by NK cells is partly mediated by molecules termed natural cytotoxicity receptors (NCRs). In the present study, we hypothesize that it is possible to endow T-cells with an NK recognition pattern, providing them with a mean to recognize tumor cells, in a non-MHC restricted way. To test this, we genetically modified human T-cells with different chimeric receptors based on the human NCR2 molecule and then assessed their antitumor activity in vitro and in vivo. Our results show that expression in primary lymphocytes of an NCR2-derived CAR, termed s4428z, confers T-cells with the ability to specifically recognize heterogeneous tumors and to mediate tumor cytotoxicity in a mouse model. This study demonstrates the benefit of combining tumor recognition capability of NK cells with T cell effectiveness to improve cancer immunotherapy.

Effect of β2-adrenergic receptor gene (ADRB2) 3' untranslated region polymorphisms on inhaled corticosteroid/long-acting β2-adrenergic agonist response

Background

Evidence suggests that variation in the length of the poly-C repeat in the 3′ untranslated region (3′UTR) of the β₂-adrenergic receptor gene (ADRB2) may contribute to interindividual variation in β-agonist response. However, methodology in previous studies limited the assessment of the effect of sequence variation in the context of poly-C repeat length. The objectives of this study were to design a novel genotyping method to fully characterize sequence variation in the ADRB2 3′UTR poly-C repeat in asthma patients treated with inhaled corticosteroid and long-acting β₂-adrenergic agonist (ICS/LABA) combination therapy, and to analyze the effect of the poly-C repeat polymorphism on clinical response.

Methods

In 2,250 asthma patients randomized to treatment with budesonide/formoterol or fluticasone/salmeterol in a six-month study (AstraZeneca study code: SD-039-0735), sequence diversity in the ADRB2 poly-C repeat region was determined using a novel sequencing-based genotyping method. The relationship between the poly-C repeat polymorphism and the incidence of severe asthma exacerbations, and changes in pulmonary function and asthma symptoms from baseline to the average during the treatment period, were analyzed.

Results

Poly-C repeat genotypes were assigned in 97% (2,192/2,250) of patients. Of the 13 different poly-C repeat alleles identified, six alleles occurred at a frequency of >5% in one or more population in this study. The repeat length of these six common alleles ranged from 10 to 14 nucleotides. Twelve poly-C repeat genotypes were observed at a frequency of >1%. No evidence of an association between poly-C repeat genotype and the incidence of severe asthma exacerbations was observed. Patients’ pulmonary function measurements improved and asthma symptoms declined when treated with ICS/LABA combination therapy regardless of poly-C repeat genotype.

Conclusions

The extensive sequence diversity present in the poly-C repeat region of the ADRB2 3′UTR did not predict therapeutic response to ICS/LABA therapy.

PeakSeeker: a program for interpreting genotypes of mononucleotide repeats

Background

Mononucleotide repeat microsatellites are abundant, highly polymorphic DNA sequences, having the potential to serve as valuable genetic markers. Use of mononucleotide microsatellites has been limited by their tendency to produce "stutter", confounding signals from insertions and deletions within the mononucleotide tract that occur during PCR, which complicates interpretation of genotypes by masking the true position of alleles. Consequently, microsatellites with larger repeating subunits (dinucleotide and trinucleotide motifs) are used, which produce less stutter but are less genetically heterogeneous and less informative. A method to interpret the genotypes of mononucleotide repeats would permit the widespread use of those highly informative microsatellites in genetic research.

Findings

We have developed an approach to interpret genotypes of mononucleotide repeats using a software program, named PeakSeeker. PeakSeeker interprets experimental electropherograms as the most likely product of signals from individual alleles. Because mononucleotide tracts demonstrate locus-specific patterns of stutter peaks, this approach requires that the genotype pattern from a single allele is defined for each marker, which can be approximated by genotyping single DNA molecules or homozygotes. We have evaluated the program's ability to discriminate various types of homozygous and heterozygous mononucleotide loci using simulated and experimental data.

Conclusion

Mononucleotide tracts offer significant advantages over di- and tri-nucleotide microsatellite markers traditionally employed in genetic research. The PeakSeeker algorithm provides a high-throughput means to type mononucleotide tracts using conventional and widely implemented fragment length polymorphism genotyping. Furthermore, the PeakSeeker algorithm could potentially be adapted to improve, and perhaps to standardize, the analysis of conventional microsatellite genotypes.

A genome-wide microsatellite polymorphism database for the indica and japonica rice

Microsatellite (MS) polymorphism is an important source of genetic diversity, providing support for map-based cloning and molecular breeding. We have developed a new database that contains 52 845 polymorphic MS loci between indica and japonica, composed of ample Class II MS markers, and integrated 18 828 MS loci from IRGSP and genetic markers from RGP. Based on genetic marker positions on the rice genome (http://rise.genomics.org.cn/rice2/index.jsp ), we determined the approximate genetic distances of these MS loci and validated 100 randomly selected markers experimentally with 90% success rate. In addition, we recorded polymorphic MS positions in indica cv. 9311 that is the most important paternal parent of the two-line hybrid rice in China. Our database will undoubtedly facilitate the application of MS markers in genetic researches and marker-assisted breeding. The data set is freely available from www.wigs.zju.edu.cn/achievment/polySSR.

Homozygosity mapping as a screening tool for the molecular diagnosis of hereditary skin diseases in consanguineous populations

BACKGROUND

The routine diagnosis of genodermatoses is significantly complicated by the fact that in this group of disorders, clinical manifestations may result from mutations in unrelated genes (genetic heterogeneity) and mutations in the same gene often lead to dissimilar clinical signs (phenotypic heterogeneity).

METHODS

In this study, we applied the principles of homozygosity mapping as a screening method before formal mutational analysis in an attempt to facilitate the molecular diagnosis of genodermatoses in consanguineous families. The method was evaluated in a retrospective fashion in 4 families previously assessed with junctional epidermolysis bullosa and in a prospective manner in 11 families with congenital recessive ichthyosis.

RESULTS

The method was found to be efficient in directing the molecular analysis to one of the 4 genes commonly involved in the pathogenesis of junctional epidermolysis bullosa or in identifying cases of congenital recessive ichthyosis caused by mutations in TGM1. We found that this diagnostic strategy results in a 5-fold decrease in the cost of mutation analysis.

LIMITATIONS

The proposed diagnostic strategy is applicable to consanguineous families only and, therefore, cannot be used in outbred populations.

CONCLUSION

Our results indicate that homozygosity mapping may serve as a useful adjunct in the molecular diagnosis of junctional epidermolysis bullosa or congenital recessive ichthyosis in inbred populations. This study emphasizes the usefulness in human genetics of diagnostic strategies tailored to the demographic features of target populations.

Has Simple Sequence Repeat Mutability Been Selected to Facilitate Evolution?

While adaptation and speciation begin with heritable variation, the underlying processes of mutation remain poorly understood. One particularly interesting source for prolific and adaptively meaningful variation is presented by the exceptionally high mutability of simple sequence repeats (SSRs: microsatellites and minisatellites). Frequent mutations at SSR sites alter the number of tandem repeats and create extensive polymorphism. Although most SSR variants are commonly presumed to be neutral, SSR variation has been shown to influence many biochemical, morphological, physiological, and behavioral characters, with at least a few examples offering evidence of response to selection. The type and degree of phenotypic variation depend upon each SSR's motif and on its location in exon, intron, or regulatory region, but the generation of abundant repeat-number variation is intrinsic to all of these repetitive sequences. Given the widespread distribution of SSRs within most genomes and their potential to modify almost any aspect of gene function, we believe that SSR mutability can facilitate evolutionary adaptation. Furthermore, we argue that the properties of SSRs allow natural selection to favor, indirectly, the mutability of these sites, in contrast to a conventional expectation that selection normally minimizes mutation rates by balancing the cost of deleterious mutations against the cost of replication fidelity. We believe that SSR mutability is not an "accident" of DNA replication, but has been adjusted and selected for this role. SSRs thus have a true biological function as general-purpose "tuning knobs" whereby mutations provide reversible adjustment for many quantitative and qualitative traits.