Use of retrotransposon-derived genetic markers to analyse genomic variability in plants

Transposable elements (TEs) are common mobile genetic elements comprising several classes and making up the majority of eukaryotic genomes. The movement and accumulation of TEs has been a major force shaping the genes and genomes of most organisms. Most eukaryotic genomes are dominated by retrotransposons and minimal DNA transposon accumulation. The ‘copy and paste’ lifecycle of replicative transposition produces new genome insertions without excising the original element. Horizontal TE transfer among lineages is rare. TEs represent a reservoir of potential genomic instability and RNA-level toxicity. Many TEs appear static and nonfunctional, but some are capable of replicating and mobilising to new positions, and somatic transposition events have been observed. The overall structure of retrotransposons and the domains responsible for the phases of their replication are highly conserved in all eukaryotes. TEs are important drivers of species diversity and exhibit great variety in their structure, size and transposition mechanisms, making them important putative actors in evolution. Because TEs are abundant in plant genomes, various applications have been developed to exploit polymorphisms in TE insertion patterns, including conventional or anchored PCR, and quantitative or digital PCR with primers for the 5ʹ or 3ʹ junction. Alternatively, the retrotransposon junction can be mapped using high-throughput next-generation sequencing and bioinformatics. With these applications, TE insertions can be rapidly, easily and accurately identified, or new TE insertions can be found. This review provides an overview of the TE-based applications developed for plant species and assesses the contributions of TEs to the analysis of plants’ genetic diversity.

Ligation-anchored PCR unveils immune repertoire of TCR-beta from whole blood

Background As one of the genetic mechanisms for adaptive immunity, V(D)J recombination generates an enormous repertoire of T-cell receptors (TCRs). With the development of high-throughput sequencing techniques, systematic exploration of V(D)J recombination becomes possible. Multiplex PCR method has been previously developed to assay immune repertoire, however the usage of primer pools has inherent bias in target amplification. In our study, we developed a ligation-anchored PCR method to unbiasedly amplify the repertoire. Results By utilizing a universal primer paired with a single primer targeting the conserved constant region, we amplified TCR-beta (TRB) variable regions from total RNA extracted from blood. Next-generation sequencing libraries were then prepared for Illumina HiSeq 2500 sequencer, which provided 151 bp read length to cover the entire V(D)J recombination region. We evaluated this approach on blood samples from patients with malignant and benign meningiomas. Mapping of sequencing data showed 64% to 91% of mapped TCRV-containing reads belong to TRB subtype. An increased usage of TRBV29-1 was observed in malignant meningiomas. Also distinct signatures were identified from CDR3 sequence logos, with predominant subset as 42 nt for benign and 45 nt for malignant samples, respectively. Conclusions In summary, we report an integrative approach to monitor immune repertoire in a systematic manner.