Miniature Inverted-repeat Transposable Elements (MITEs) and their Relationship with Established DNA Transposons

I. The discovery of MITEs in plant and animal genomes II. Organizing the diversity of MITEs III. The Tc1/mariner superfamily as a source of MITEs A. MITEs related to Tc1/mariner transposons in C. elegans B. MITEs related to Tc1/mariner transposons in humans C. MITEs related to Tc1/mariner transposons in insects D. MITEs related to Tc1/mariner transposons in plants IV. Tourist-like MITEs are related to members of the PIF/Harbinger superfamily A. The maize P Instability Factor (PIF) and the miniature PIF (mPIF) MITE B. PIF-like elements and their MITEs in other organisms V. Other MITEs and nonautonomous DNA transpsons A. Other MITEs B. Helitrons: rolling-circle transposons in eukaryotes VI. A model for the origin of MITEs 3 I. The discovery of MITEs in plant and animal genomes A 128 bp insertion in a mutant maize waxy gene (the wxB2 allele) led to the identification of a group of related elements called Tourist in the untranslated regions of genes from diverse grass species (5, 7). A 257-bp insertion in a sorghum Tourist element led to the discovery of a second family of elements called Stowaway, in the genes of a diversity of flowering plants (6). Tourist and Stowaway elements share structural but not sequence similarity. Both are short (~100 to 500 bp), have conserved terminal repeats, have target site preference (Tourist, TAA; Stowaway, TA) and, of most significance for this chapter, have no coding potential. All of these features are reminiscent of the nonautonomous members of some DNA transposon families. However, it was the high copy number of Tourist and Stowaway elements and the uniformity of related elements that served to set them apart from previously described nonautonomous elements. For this reason, and because they were being mistakenly classified as SINEs, it was decided to name these and other structurally related elements miniature inverted-repeat transposable elements, or MITEs (4, 64). Although first discovered in plants, MITEs were soon found in several animal genomes including C. With the advent of genome sequencing projects, vast amounts of DNA sequence, from a wide variety of plant and animal species, has become available for analysis. MITES, with their high copy number, distinct structural features (target site 4 duplications, TSDs and terminal inverted repeats, TIRs) and compact stature, are relatively easy to mine from DNA sequence databases. As such, the number of MITEs and MITE families has proliferated in the literature much as the MITEs themselves have …