Fixed and unstable <i>I</i>-related transposable elements in heterochromatin of <i>Drosophila melanogaster</i>

Abstract

Transposable elements are disproportionately abundant in the heterochromatin of Drosophila melanogaster. Among the forces contributing to this bias in genomic distribution, fixation due to positive selection has been put forward. We have studied I-related elements which are located in pericentromeric heterochromatin and are believed to have a role in the control of active I elements. Flies straight from the wild have been studied where fixed elements are expected to emerge clearly over the highly polymorphic background in the genomic distribution of transposable elements. The results show that some restriction fragments due to I-related elements are conserved in size and are present in all individuals tested, consistent with a selective pressure for a role. Other fragments are polymorphic in presence/absence and intensity in individuals from the wild but appear homogeneous in laboratory stocks. Although the significance of this type of instability is unclear, the finding that these polymorphic bands are recurrent in populations from distant geographical locations is also suggestive of a selective pressure for a role.

An old bilbo-like non-LTR retroelement insertion provides insight into the relationship of species of the virilis group

“…Few apparent fixations or near-fixations, at the population or species level, have been described in Drosophila, both in the recombining euchromatin (Maside et al, 2002;Petrov et al, 2003;Catania et al, 2004;Schlenke and Begun, 2004;Lipatov et al, 2005), non-recombining euchromatin (Bartolomé and Maside, 2004), and non-recombining heterochromatin (Maside et al, 2005;Junakovic et al, 2005).…”

Amplification of the 1731 LTR retrotransposon in Drosophila melanogaster cultured cells: Origin of neocopies and impact on the genome

“…A fraction of TEs is composed of elements which show a retrovirus-like structure, LTR-retrotransposons, which were the first TEs to be described as moderately repeated dispersed genetic elements in Drosophila melanogaster (Finnegan et al, 1978;Ilyin et al, 1978). TEs belonging to a given family may occupy different genomic locations in either euchromatin or heterochromatin, even amongst individuals of the same population (Montgomery and Langley, 1983;Petrov et al, 2003;Junakovic et al, 2005). The impact of TEs at the genome level has been examined in both animal and plant species (Arkhipova, 2001;Casacuberta and Santiago, 2003;Deininger et al, 2003), with specific focus on their role in the structure of heterochromatin and telomeres (Pimpinelli et al, 1995;Pardue et al, 1997).…”