Fig. 1
From: Transposable element-derived sequences in vertebrate development
Adaptive mechanisms of TE-derived sequences evolution leading to developmental innovations. After the insertion of a TE: a in an intron of a protein-coding gene, part of the TE can give rise to a new exon (exonization). Splicing sites can either be directly present in the TE sequence or can be acquired by mutations. b part of the TE can form a new host gene and be transcribed from either a flanking host promoter or a promoter derived from the TE sequence itself. c the TE can form a new long non-coding RNA (lncRNA) gene and be transcribed from either a flanking host promoter or a promoter derived from the TE sequence itself. d-e in the upstream region of a coding or RNA gene, the TE can form a new promoter (D) or enhancer (this model also works for TE-derived silencers) (e). f the TE can form an insulator region, which recruits the CCCTC-binding factor (CTCF) and blocks heterochromatin spreading, allowing the expression of downstream sequences. Red boxes correspond to TEs and blue boxes to exapted TE sequences