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Mob Genet Elements
2011 Nov 01;14:296-300. doi: 10.4161/mge.18550.
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Expression of DNA transposable elements during nervous system development: A discussion about its possible functions.
Faunes F
,
Lee-Liu D
,
Larrain J
.
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Transposable elements (retrotransposons and DNA transposons) comprise a large proportion of animal genomes, for example 20% in D. melanogaster, 36% in X. tropicalis and 45% in humans. After invading a new genome, the transposable element increases its copy number and subsequently accumulates mutations. These may eventually result in inactive copies. Until recent days transposons have been considered "junk" DNA and no clear function have been assigned for this important amount of information on genomes.
Figure 1. Putative structure of Tc1–2_Xt transposable element and expression during development. (A) The sequence analysis of the 116 copies of the Tc1–2_Xt transposable element in the X. tropicalis genome showed the typical structure of Tc1-like elements. The length of this element is 1,581 bases. It is flanked by two inverted repeats (IR) containing two direct repeats (white triangles) for the binding of the transposase. The transposase ORF (green) contains a putative DNA binding domain (blue) and the catalytic triad (red, aspartic-aspartic-glutamic residues (DDE)). Five copies in the genome could code for an intact transposase. (B) Schematic representation of the expression of Tc1–2_Xt during X. tropicalis early development. The expression of Tc1–2_Xt is shown in blue for early stages of X. tropicalis development. No expression is detected before the beggining of the zygotic transcription (st.6 is shown as an example, lateral view). Expression is clearly detected from gastrula stage (st.10) in the Spemann’s organizer and then in anterior and neural tissues. Views are indicated in brackets. CNS, central nervous system. Figures were downloaded from http://www.xenbase.org/anatomy/static/NF/NF-all.jsp and modified according to the expression pattern obtained by in situ hybridization.
Figure 2. Transposition reporter construct. The reporter construct contains an egfp open reading frame with an insertion of a random sequence (same length as the original transposase). When transposase mRNA is present (either exogenous, when working in vitro, or endogenous, when in vivo) and an active transposase is being translated, transposition will occur, rendering EGFP+ cells. Note that transposition footprint is in frame with the egfp gene. The random sequence insertion sites can then be characterized using deep sequencing of reverse PCR amplicons. IR- inverted repeat. EGFP-enhanced green fluorescent protein. pA-polyadenylation signal. NNN-transposition footprint.
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