Abundance and chromosomal distribution of six Drosophila buzzatii transposons: BuT1, BuT2, BuT3, BuT4, BuT5, and BuT6

Abstract

The abundance and chromosomal distribution of six class-II transposable elements (TEs) of Drosophila buzzatii have been analyzed by Southern blotting and in situ hybridization. These six transposons had been previously found at the breakpoints of inversions 2j and 2q ( 7 ) of D. buzzatii. These two polymorphic inversions were generated by an ectopic recombination event between two copies of Galileo, a Foldback element. The four breakpoints became hotspots for TE insertions after the generation of the inversion and the transposons analyzed in this work are considered to be secondary invaders of these regions. Insertions of the six transposons are present in the euchromatin but show an increased density in the pericentromeric euchromatin-heterochromatin transition region and the dot chromosome. They are also more abundant in the inverted segments of chromosome 2 rearrangements. We further observed that the accumulation of TE insertions varies between elements and is correlated between dot, proximal regions, and inverted segments. These observations fully agree with previous data in Drosophila melanogaster and support recombination rate as the chief force explaining the chromosomal distribution of TEs.

Characterization and Genomic Organization of <i>PERI</i>, a Repetitive DNA in the <i>Drosophila buzzatii</i> Cluster Related to <i>DINE-1</i> Transposable Elements and Highly Abundant in the Sex Chromosomes

“…Only a few euchromatic signals were observed, although we cannot exclude the possibility that a few dispersed euchromatic copies of PERI remain undetected. Such a pattern of TE accumulation reflects the distribution of genomic regions featuring reduced rates of meiotic recombination and it is most likely to be a consequence of it [Charlesworth et al, 1994;Pimpinelli et al, 1995;Casals et al, 2006]. Interestingly, the distribution of PERI does not seem to overlap with the distribution of the pBuM satDNA in any chromosome, including the X chromosome, where both repetitive DNAs were found in the heterochromatin ( fig.…”

“…However, the authors noticed that the pattern of hybridization signals generated by cDk27 (probably ␤ -heterochromatin) was different from those detected in the tightly compacted ␣ -heterochromatin, characteristic for satDNAs. In another study, Casals et al [2005Casals et al [ , 2006 showed a preferential accumulation of several class-II transposable elements in pericentromeric zones of polytene chromosomes, defined as transitions between heterochromatin and euchromatin (probably ␤ -heterochromatin). Finally, using PCR, we did not find evidence of interspersion between one of the class II TE elements ( Galileo ) analysed by Casals et al [2005Casals et al [ , 2006, and satDNA repeats [Kuhn et al, 2009].…”

“…In another study, Casals et al [2005Casals et al [ , 2006 showed a preferential accumulation of several class-II transposable elements in pericentromeric zones of polytene chromosomes, defined as transitions between heterochromatin and euchromatin (probably ␤ -heterochromatin). Finally, using PCR, we did not find evidence of interspersion between one of the class II TE elements ( Galileo ) analysed by Casals et al [2005Casals et al [ , 2006, and satDNA repeats [Kuhn et al, 2009]. Thus, the available information suggests non-overlapping patterns or low levels of interspersion between the verified TEs and satDNAs in the buzzatii cluster.…”

A Divergent P Element and Its Associated MITE, BuT5, Generate Chromosomal Inversions and Are Widespread within the Drosophila repleta Species Group

“…BuT5 is also quite abundant. In D. buzzatii, BuT5 was found (using in situ hybridization to polytene chromosomes) to be the most abundant of a set of seven transposons, with a basal density of 10 − 2 copies per genome and chromosomal band (Casals et al 2006). BuT5 is particularly abundant as secondary colonizer of the inversion breakpoints, indicating that it is (or has been until very recently) transpositionally active (Delprat et al 2009).…”

“…The three inversions were caused by ectopic recombination between copies of Galileo , a P -superfamily transposon (Marzo et al 2008), and BuT5 was a secondary colonizer of the inversion breakpoints. The secondary colonization of breakpoints in recent polymorphic inversions (Casals et al 2003; Delprat et al 2009) and the relatively high abundance of BuT5 in different D. buzzatii strains (Casals et al 2006) indicate current or recent transpositional activity of BuT5 in D. buzzatii . Furthermore, recent works in our group have revealed that BuT5 generated two recently fixed inversions in two repleta group species, 2s in D. mojavensis (Guillén and Ruiz 2012), and 2x 3 in D. uniseta (Prada 2010).…”