Long Interspersed Nucleotide Elements (LINEs) Rami Al-Ouran

Transposable elements (TEs) occupy 46% of the human genome Two classes of TEs: – DNA transposons – RNA transposons (retrotransposons or retroelements) Retroelements: – Long terminal repeats (LTR) – non-LTR (LINE) LINEs occupy over 35% of the human genome!!!

Introduction Non-LTR include: – Autonomous members: Long Interspersed Elements (LINE) – Non autonomous members: ALU, SINE In mammals LINE1 is the predominant LINE element TE activity leads to: – Genomic mutations – Interference with gene expression

Definition of LINE1 LINE1 is – an autonomous TE – about 6 kb long – that propagates in the genome by making RNA copies of themselves – and then reverse transcribed and integrated into the genome. Encodes two open reading frames ORF1 and ORF2 required for L1 retransposition From Belancio et al., GenomeMedicine 1:97, (2009)

Structure of LINE1 5’UTRORF1ORF23’UTR 5’UTR that contains an internal promoter ORF1 which encodes protein ORF1p or p40 Inter-ORF linker region ORF2 which encodes ORF2p 3’UTR containing a functional polyadenylation signal

From Belancio et al., GenomeMedicine 1:97, (2009) Lifecycle of LINE1

L1 integration reaction. From Babushok et al. Human Mutation (2007)

Lifecycle of LINE1 a)Transcription. Initiation of transcription. b)Before leaving the nucleus the number of of L1 transcripts can be reduced by RNA processing c)Translation. L1 enters the cytoplasm for translation to produce ORF1 and ORF2 proteins are produced which are needed for retransposition. RNP(ribonucleoprotein particle) is formed d)Insertion of new L1 copy. This could lead to DSB or to TPRT (Target Primed Reverse Transcription)

LINE1 and Disease 1.Insertion of new element copies – In 1991 the discovery of first known active human L1 was from its retrotransposition into the factor VIII gene causing hemophilia – The random insertion process leads to diversity in gene diseases – In breast cancer BRCA1 and BRCA2 are disrupted by TE insertion 2.Interference with gene expression – Insertion of the retroelement disrupts the gene function and gene expression

LINE1 and DSBs Formation of DNA DSBs is associated with L1 expression Depends on the enzymatic activity of the L1 ORF2 endonuclease domain

Conclusions LINEs are long interspersed retro elements Account for almost 35% of human genome LINE1 can cause human disease by insertion and modifying gene expression LINE1 can lead to DSB

References Belancio VP, Deininger PL, Roy-Engel AM: LINE dancing in the human genome: transposable elements and disease. Genome Med. (2009) Oct 27;1(10):97. Babushok, D. V. and Kazazian, H. H. (2007), Progress in understanding the biology of the human mutagen LINE-1. Human Mutation, 28: 527–539. doi: /humu.20486