In a multicellular organism, the genomes of all cells are in general the same. Programmed DNA elimination is a notable exception to this genome constancy rule. DNA elimination removes genes and repetitive elements in the germline genome to form a reduced somatic genome in various organisms. The process of DNA elimination within an organism is highly accurate and reproducible; it typically occurs during early embryogenesis, coincident with germline-soma differentiation. DNA elimination provides a mechanism to silence selected genes and repeats in somatic cells. Recent studies in nematodes suggest that DNA elimination removes all chromosome ends, resolves sex chromosome fusions, and may also promote the birth of novel genes. Programmed DNA elimination processes are diverse among species, suggesting DNA elimination likely has evolved multiple times in different taxa. The growing list of organisms that undergo DNA elimination indicates that DNA elimination may be more widespread than previously appreciated. These various organisms will serve as complementary and comparative models to study the function, mechanism, and evolution of programmed DNA elimination in metazoans.
Long Terminal Repeat (LTR) retrotransposons replicate through “copy and paste” mechanisms mediated by reverse transcription in virus-like particles (VLPs) and integration in the nucleus (see article from Lee and Martienssen, pp. 2241–2251). VLP DNA-sequencing reveals complementary DNA (cDNA) replication intermediates from active retrotransposons. Instead of functional linear intermediates that integrate in the nucleus, the Arabidopsis retroelement SISYPHUS lacks features important for nuclear import, and instead accumulates circular cDNA from futile autointegration within the VLP. In Greek mythology, Sisyphus was condemned to the futile task of rolling a huge boulder uphill eternally. Image created and provided Seung Cho Lee, Evan Ernst, and Robert A. Martienssen.
Programmed DNA elimination: silencing genes and repetitive sequences in somatic cells
Maxim V. Zagoskin, Jianbin Wang; Programmed DNA elimination: silencing genes and repetitive sequences in somatic cells. Biochem Soc Trans 1 November 2021; 49 (5): 1891–1903. doi: https://doi.org/10.1042/BST20190951
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