Kaul Tiffany, Morales Maria E, Smither Emily, Baddoo Melody, Belancio Victoria P, Deininger Prescott
Tulane Cancer Center, Tulane University.
Tulane Cancer Center, Tulane University; Department of Pathology, Tulane University.
J Vis Exp. 2019 May 19(147). doi: 10.3791/59771.
Long INterspersed Elements-1 (LINEs/L1s) are repetitive elements that can copy and randomly insert in the genome resulting in genomic instability and mutagenesis. Understanding the expression patterns of L1 loci at the individual level will lend to the understanding of the biology of this mutagenic element. This autonomous element makes up a significant portion of the human genome with over 500,000 copies, though 99% are truncated and defective. However, their abundance and dominant number of defective copies make it challenging to identify authentically expressed L1s from L1-related sequences expressed as part of other genes. It is also challenging to identify which specific L1 locus is expressed due to the repetitive nature of the elements. Overcoming these challenges, we present an RNA-Seq bioinformatic approach to identify L1 expression at the locus specific level. In summary, we collect cytoplasmic RNA, select for polyadenylated transcripts, and utilize strand-specific RNA-Seq analyses to uniquely map reads to L1 loci in the human reference genome. We visually curate each L1 locus with uniquely mapped reads to confirm transcription from its own promoter and adjust mapped transcript reads to account for mappability of each individual L1 locus. This approach was applied to a prostate tumor cell line, DU145, to demonstrate the ability of this protocol to detect expression from a small number of the full-length L1 elements.
长散在核元件-1(LINEs/L1s)是可在基因组中复制并随机插入的重复元件,会导致基因组不稳定和诱变。了解L1基因座在个体水平的表达模式将有助于理解这种诱变元件的生物学特性。这种自主元件占人类基因组的很大一部分,有超过50万份拷贝,尽管99%是截短和有缺陷的。然而,它们的丰度以及大量有缺陷的拷贝使得从作为其他基因一部分而表达的L1相关序列中鉴定真正表达的L1具有挑战性。由于这些元件的重复性,鉴定哪个特定的L1基因座被表达也具有挑战性。为克服这些挑战,我们提出一种RNA测序生物信息学方法来鉴定基因座特异性水平的L1表达。总之,我们收集细胞质RNA,选择聚腺苷酸化转录本,并利用链特异性RNA测序分析将读数唯一地映射到人类参考基因组中的L1基因座。我们用唯一映射的读数直观地筛选每个L1基因座,以确认其自身启动子的转录,并调整映射的转录本读数以考虑每个L1基因座的可映射性。该方法应用于前列腺肿瘤细胞系DU145,以证明该方案检测少数全长L1元件表达的能力。