MODERN THOUGHTS ON AN ANCYENT MARINERE: Function, Evolution, Regulation

Abstract

The mariner/Tc1 superfamily of transposable elements is one of the most diverse and widespread Class II transposable elements. Within the larger assemblage, the mariner-like elements (MLEs) and the Tc1-like elements (TLEs) are distinct families differing characteristically in the composition of the "D,D(35)E" cation-binding domain. Based on levels of sequence similarity, the elements in each family can be subdivided further into several smaller subfamilies. MLEs and TLEs both have an extraordinarily wide host range. They are abundant in insect genomes and other invertebrates and are found even in some vertebrate species including, in the case of mariner, humans, in which one element on chromosome 17p has been implicated as a hotspot of recombination. In spite of the extraordinary evolutionary success of the elements, virtually nothing is known about their mode of regulation within genomes. There is abundant evidence that the elements are disseminated to naive host genomes by horizontal transmission, and there is a substantial base of evidence for inference about the subsequent population dynamics. Studies of engineered mariner elements and induced mutations in the transposase have identified two mechanisms that may be operative in mariner regulation. One mechanism is overproduction inhibition, in which excessive wild-type transposase reduces the rate of excision of a target element. A second mechanism is dominant-negative complementation, in which certain mutant transposase proteins antagonize the activity of the wild-type transposase. The latter process may help explain why the vast majority of MLEs in nature undergo "vertical inactivation" by multiple mutations and, eventually, stochastic loss. There is also evidence that mariner/Tc1 elements can be mobilized in hybrid dysgenesis; in particular, certain dysgenic crosses in Drosophila virilis result in mobilization of a TLE designated Paris as well as the mobilization of other unrelated transposable elements.

Revisiting horizontal transfer of transposable elements in Drosophila

“…HT of a functional element to a naïve genome or reintroduction into the primary host genome can therefore prevent its extinction. This fact was illustrated by Hartl et al (1997) for the mariner element.…”

“…Using such estimates as indicators of divergence, other comparisons would indicate a lesser divergence than expected, which would then mistakenly be suggested as HT (Malik et al, 1999). So sequence similarity deserves careful analysis, since genomes of several species have been shown to harbor more than one subfamily of a particular TE, such as mariner (Robertson and MacLeod, 1993;Robertson and Lampe, 1995;Hartl et al, 1997), gypsy (Hochstenbach et al, 1996;Martínez-Sebastián et al, 2002;Heredia et al, 2004) and P element (Clark and Kidwell, 1997), among others.…”

In vivo transposition of mariner -based elements in enteric bacteria and mycobacteria

“…The genomes of diverse eukaryotic organisms have been found to contain members of the mariner͞Tc1 superfamily of transposable elements (7)(8)(9). Elements of this superfamily share certain amino acid identities, have similar overall organization, and have similar ''cut-and-paste'' mechanisms of transposition (10)(11)(12).…”

Transposon Mutagenesis of Trypanosoma brucei Identifies Glycosylation Mutants Resistant to Concanavalin A

“…On the other hand, transposon mutagenesis could potentially provide a valuable tool for forward genetics in T. brucei. Members of the mariner/ Tc1 superfamily are probably the most widespread DNA transposons in nature (17,18). Transposition occurs via a nonreplicative cut-and-paste mechanism, in which a staggered doublestranded break at each end of the transposable element releases it from the donor DNA molecule, freeing it to be ligated into a staggered cut at the target site (19).…”