Enhancer action in trans is permitted throughout the Drosophila genome

Abstract

Interactions between paired homologous genes can lead to changes in gene expression. Such trans-regulatory effects exemplify transvection and are displayed by many genes in Drosophila, in which homologous chromosomes are paired somatically. Transvection involving the yellow cuticle pigmentation gene can occur by at least two mechanisms, one involving the trans-action of enhancers on a paired promoter and a second involving pairingmediated bypass of a chromatin insulator. A system was developed to evaluate whether the action of the yellow enhancers in trans could be reconstituted outside of the natural near telomeric location of the yellow gene. To this end, transgenic flies were generated that carried a yellow gene modified by the inclusion of strategically placed recognition sites for the Cre and FLP recombinases. Independent action of the recombinases produced a pair of derivative alleles, one enhancerless and the other promoterless, at each transgene location. Transvection between the derivatives was assessed by the degree of interallelic complementation. Complementation was observed at all eight sites tested. These studies demonstrate that yellow transvection can occur at multiple genomic locations and indicate that the Drosophila genome generally is permissive to enhancer action in trans. G ene expression is controlled by regulatory elements that modulate transcription in appropriate temporal and spatial patterns. In eukaryotes, these control elements often reside in large, complex regions, requiring action over long distances to elicit changes in transcription of a target promoter. In some cases, the control elements of paired homologous genes can interact in trans to alter gene expression. Such trans-regulatory effects illustrate processes known as transvection. Transvection was described first in Drosophila (1), which has homologous chromosomes that are paired somatically. Transvection and related processes have been reported in many organisms besides Drosophila (for example, refs. 2-7, and reviewed in refs. 8-11). These observations suggest that transvection may be generally possible for eukaryotic control regions and that these processes may be important for the normal regulation of some genes. For example, chromosomal pairing is proposed to play a role in gene silencing associated with imprinting and X chromosome inactivation (4, 12).In Drosophila, interactions between homologous chromosomes can have either a positive or negative effect on transcription. Examples of negative effects include repression of white gene expression by certain alleles of zeste, trans silencing conferred by the insertion of a block of heterochromatin near the brown gene, and pairing-dependent silencing, as exemplified by the effects of Polycomb response elements (reviewed in refs. 8-11, 13, and 14). Examples of positive effects include events at the Ultrabithorax, Abdominal B, decapentaplegic, yellow, and eyes absent genes (1,(15)(16)(17)(18)(19)(20)(21)(22)(23)(24).A useful system for studying the mechanisms involved in posi...

Comparing Enhancer Action in Cis and in Trans

“…Our approach was informed by a prior experiment that used transposons carrying yellow alleles, including flanking regulatory sequences, that were designed to mimic mutations known to support enhancer action in trans at the natural yellow locus. That study showed the Drosophila genome to be generally permissive to transvection, demonstrating the feasibility of a transgenic approach to the analysis of enhancer action in trans (Chen et al 2002). In the present study, our goal was to construct transgenes based on fluorescent reporters such as GFP and mCherry to facilitate quantification of gene expression and to provide cellular resolution of transgene activation.…”

Enhancer Blocking and Transvection at the DrosophilaapterousLocus

“…Since this special set of mutations is required to detect transvection, it is unknown exactly how prevalent transvection is in Drosophila. However, on the basis of known pairing frequencies of homologous loci (Golic and Golic 1996b;Vazquez et al 2002;Lowenstein et al 2004;Harmon and Sedat 2005) and the work of Chen et al (2002), in which it was shown using a Cre and FLPmediated transgene coplacement system that the Drosophila genome is generally permissive for transvection, it is likely that the dozen or so known instances of transvection represent only a small fraction of all transregulatory effects in Drosophila.…”

The Capacity to Act in Trans Varies Among Drosophila Enhancers

“…Evidence for enhancer action in trans has been uncovered at a handful of genes in the Drosophila genome, often providing an explanation for unexpected intragenic complementation of loss-of-function alleles (Lewis 1954;Gelbart 1982;Geyer et al 1990;Leiserson et al 1994;Hendrickson and Sakonju 1995;Casares et al 1997;Morris et al 1998;Southworth and Kennison 2002;Marin et al 2004;Coulthard et al 2005;Gohl et al 2008;Juni and Yamamoto 2009) paired mutant and wild-type alleles (Gibson et al 2000;Lum and Merritt 2011;Bing et al 2014). More recently, transgenic approaches based on site-specific recombination have been developed for Drosophila to query specific enhancer fragments and genomic positions for support of transvection (Chen et al 2002;Kravchenko et al 2005;Bateman et al 2012a;Mellert and Truman 2012; also see Kassis et al 1991). Thus far, transvection has been observed at all genomic insertion sites tested, suggesting that the Drosophila genome is generally permissive to enhancer action in trans.…”

“…More recently, transgenic approaches based on site-specific recombination have been developed for Drosophila to query specific enhancer fragments and genomic positions for support of transvection (Chen et al 2002;Kravchenko et al 2005;Bateman et al 2012a;Mellert and Truman 2012; also see Kassis et al 1991). Thus far, transvection has been observed at all genomic insertion sites tested, suggesting that the Drosophila genome is generally permissive to enhancer action in trans.…”