Somatizing the transposons action

Abstract

The somatic mobilization of transposable elements is more common than previously thought. In this review we discuss how the intensity and the biologic consequences of somatic mobilization are dependent on the transposable elements landscapes of each genome, and on the "momentum" of each particular TE with respect to the mechanisms that control its transposition and the possibility to escape this control. Additionally, the biologic consequences of somatic mobilization vary among organisms that show an early separation between the germline and somatic cells and those organisms that do not exhibit this separation or that reproduce asexually. In the former, somatic transposition can be involved in phenotypic plasticity, detrimental conditions such as disease, or processes such as aging. For the organisms without separation between the germ and soma, somatic mobilization can be a source of genetic variability.

Keywords: genetic mosaicism; somatic mobilization; somatic transposition; transposable elements.

Figure 1.

TE landscapes for 4 genomes: the fruit fly, Drosophila melanogaster; the coelacanth, Latimeria chalumnae; the bat, Myotis lucifugus; the human, Homo sapiens. In the bar charts, the y-axis illustrates the percentage of the genome occupied by each TE and the x-axis illustrates the genetic divergence observed among copies of each TE. The pie charts show the proportion of the genome that is occupied by each TE superfamily. The key indicates the colors representing each TE superfamily (figure modified using data obtained from www.repeatmasker.org/genomicDatasets/RMGenomicDatasets.html).

Figure 2.

Somatic mobilization of transposable elements in diverse organisms showing phenotypic variegation. A) African violets (Saintpaulia sp.) with a variegated pattern promoted by an hAT transposon; B) Drosophila eye variegation promoted by the mariner element; C) a variegated rose (Rosa sp), promoted by an undetermined transposon (Photos by E. Loreto).

Figure 3.

Diagrammatic representation of the biologic consequences of somatic mobilization, which can be classed as adaptive, neutral or detrimental.

Figure 4.

The ontological phase of transposition events and their effects on mosaicism (different colors). A) Transposition occurring during embryogenesis results in mutations in large areas of the body (red), while transposition occurring posteriorly results in small-area mutations (green). B) Transposition occurring during all life stages results in mosaicism with different sizes of mosaic areas.