Genetical Research



Rates of movement and distribution of transposable elements in Drosophila melanogaster: in situ hybridization vs Southern blotting data


XULIO  MASIDE  a1 c1, CAROLINA  BARTOLOMÉ  a1, STAVROULA  ASSIMACOPOULOS  a2 and BRIAN  CHARLESWORTH  a1
a1 Institute for Cell, Animal and Population Biology, University of Edinburgh, Ashworth Laboratories, Edinburgh EH9 3JT, UK
a2 Department of Pharmacology and Physiology, University of Chicago, Chicago, IL 60637, USA

Abstract

Genomic copy numbers and the rates of movement of nine families of transposable elements (TEs) of Drosophila melanogaster were estimated in two sets of mutation accumulation lines: Beltsville and Madrid. Southern blotting was used to screen a large number of samples from both genetic backgrounds for TEs. The Madrid lines were also screened by in situ hybridization of TEs to polytene chromosomes, in order to obtain more detailed information about the behaviour of TEs in the euchromatin. Southern blotting data provided evidence of insertions and excision events in both genetic backgrounds, occurring at rates of approximately 10−5 and 10−6 per element copy per generation, respectively. In contrast, in situ data from the Madrid background presented a completely different picture, with no evidence for excisions, and a significantly higher rate of transposition (1·01×10−4). Direct comparison of the two data sets suggests that the Southern blotting technique had serious deficiencies: (i) it underestimated element abundance; (ii) it revealed less than 30% of the new insertions detected by in situ hybridization; and (iii) changes in the size of restriction fragments from any source were spuriously identified as simultaneous insertion–excision events. Our in situ data are consistent with previous studies, and suggest that selection is the main force controlling element spread by transposition.

(Received January 19 2001)
(Revised April 5 2001)


Correspondence:
c1 Corresponding author. ICAPB, Kings Buildings, University of Edinburgh, Edinburgh, EH9 3JT, UK. e-mail: xulio.maside@ed.ac.uk


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