Genetics, Vol. 178, 127-143, January 2008, Copyright © 2008
doi:10.1534/genetics.107.077768
Enhancer Blocking and Transvection at the Drosophila apterous Locus
Daryl Gohl*,
Martin Müller
,
Vincenzo Pirrotta
,
Markus Affolter
and
Paul Schedl*,1
* Department of Molecular Biology, Princeton University, Princeton, New Jersey 08544,
Department of Cell Biology, University of Basel, CH-4056 Basel, Switzerland and
Department of Molecular Biology and Biochemistry, Rutgers University, Piscataway, New Jersey 08854
1 Corresponding author: Department of Molecular Biology, Princeton University, Washington Rd., Princeton, NJ 08544.
E-mail: pschedl{at}princeton.edu
Intra- and interchromosomal interactions have been implicated in a number of genetic phenomena in diverse organisms, suggesting that the higher-order structural organization of chromosomes in the nucleus can have a profound impact on gene regulation. In Drosophila, homologous chromosomes remain paired in somatic tissues, allowing for trans interactions between genes and regulatory elements on the two homologs. One consequence of homolog pairing is the phenomenon of transvection, in which regulatory elements on one homolog can affect the expression of a gene in trans. We report a new instance of transvection at the Drosophila apterous (ap) locus. Two different insertions of boundary elements in the ap regulatory region were identified. The boundaries are inserted between the ap wing enhancer and the ap promoter and have highly penetrant wing defects typical of mutants in ap. When crossed to an ap promoter deletion, both boundary inserts exhibit the interallelic complementation characteristic of transvection. To confirm that transvection occurs at ap, we generated a deletion of the ap wing enhancer by FRT-mediated recombination. When the wing-enhancer deletion is crossed to the ap promoter deletion, strong transvection is observed. Interestingly, the two boundary elements, which are inserted
10 kb apart, fail to block enhancer action when they are present in trans to one another. We demonstrate that this is unlikely to be due to insulator bypass. The transvection effects described here may provide insight into the role that boundary element pairing plays in enhancer blocking both in cis and in trans.
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