Exonization of the LTR transposable elements in human genome
BMC GENOMICS
Authors: Piriyapongsa, Jittima; Polavarapu, Nalini; Borodovsky, Mark; McDonald, John
Abstract
Background: Retrotransposons have been shown to contribute to evolution of both structure and regulation of protein coding genes. It has been postulated that the primary mechanism by which retrotransposons contribute to structural gene evolution is through insertion into an intron or a gene flanking region, and subsequent incorporation into an exon. Results: We found that Long Terminal Repeat ( LTR) retrotransposons are associated with 1,057 human genes ( 5.8%). In 256 cases LTR retrotransposons were observed in protein-coding regions, while 50 distinct protein coding exons in 45 genes were comprised exclusively of LTR RetroTransposon Sequence ( LRTS). We go on to reconstruct the evolutionary history of an alternatively spliced exon of the Interleukin 22 receptor, alpha 2 gene ( IL22RA2) derived from a sequence of retrotransposon of the Mammalian apparent LTR retrotransposons ( MaLR) family. Sequencing and analysis of the homologous regions of genomes of several primates indicate that the LTR retrotransposon was inserted into the IL22RA2 gene at least prior to the divergence of Apes and Old World monkeys from a common ancestor (similar to 25 MYA). We hypothesize that the recruitment of the part of LTR as a novel exon in great ape species occurred prior to the divergence of orangutans and humans from a common ancestor (similar to 14 MYA) as a result of a single mutation in the proto-splice site. Conclusion: Our analysis of LRTS exonization events has shown that the patterns of LRTS distribution in human exons support the hypothesis that LRTS played a significant role in human gene evolution by providing cis-regulatory sequences; direct incorporation of LTR sequences into protein coding regions was observed less frequently. Combination of computational and experimental approaches used for tracing the history of the LTR exonization process of IL22RA2 gene presents a promising strategy that could facilitate further studies of transposon initiated gene evolution.
Identification of Multiple Complex Rearrangements Associated with Deletions in the 6q23-27 Region in Sezary Syndrome
JOURNAL OF INVESTIGATIVE DERMATOLOGY
Authors: Izykowska, Katarzyna; Zawada, Mariola; Nowicka, Karina; Grabarczyk, Piotr; Braun, Floriane C. M.; Delin, Martin; Moebs, Markus; Beyer, Marc; Sterry, Wolfram; Schmidt, Christian A.; Przybylski, Grzegorz K.
Abstract
The 6q23-27 region, recurrently deleted in Sezary syndrome (SS), was characterized at the molecular level in 13 SS patients and SS cell line SeAx. Using fine-tiling comparative genomic hybridization, deletions within the 6q23-27 region were detected in half of the samples (six patients and SeAx). All samples with deletions were further analyzed by ligation-mediated PCR. In addition, in one patient sample and in SeAx, paired-end next-generation sequencing was performed on the HiSeq2000 Illumina platform. Using those techniques, 23 rearrangements associated with the deletions were identified. The majority of rearrangements showed enormous complexity and diversity, including eight inversions, three transpositions, and four translocations (with chromosomes 3, 17, 10, and 12). Fifteen genes were disrupted by those rearrangements, the MYB proto-oncogene three times and the interleukin-22 receptor subunit alpha-2 gene (IL22RA2) twice. All three patients with MYB alterations showed low MYB expression, whereas seven of the remaining patients showed overexpression. Most patients overexpressing MYB also presented increased expression of MYC, HSPA8, and BCL2. Five gene fusions were identified, of which two, CCDC28A-IL22RA2 and AIG1-GOSR1, both in SeAx, were in the same orientation and were expressed at the messenger RNA level.