Functional Association between Eyegone and HP1a MediateswinglessTranscriptional Repression during Development

Abstract

The eyegone (eyg) gene encodes Eyg, a transcription factor of the Pax family with multiple roles during Drosophila development. Although Eyg has been shown to act as a repressor, nothing is known about the mechanism by which it represses its target genes. Here, we show that Eyg forms a protein complex with heterochromatin protein 1a (HP1a). Both proteins bind to the same chromatin regions on polytene chromosomes and act cooperatively to suppress variegation and mediate gene silencing. In addition, Eyg binds to a wingless (wg) enhancer region, recruiting HP1a to assemble a closed, heterochromatin-like conformation that represses transcription of the wg gene. We describe here the evidence that suggests that Eyg, encoded by eyegone (eyg), represses wingless (wg) during eye development by association with HP1a. We show that Eyg forms a protein complex with HP1a and both proteins colocalize on salivary gland polytene chromosomes. Using position effect variegation (PEV) experiments, we demonstrated that eyg has a dose-dependent effect on heterochromatin gene silencing and identified a genetic interaction with HP1a in this process. We further demonstrated that HP1a binds to the same wg enhancer element as Eyg. DNase I sensitivity assays indicated that this enhancer region has a closed heterochromatin-like conformation, which becomes open in eyg mutants. In these mutants, much less HP1a binds to the wg enhancer region, as shown by ChIP experiments. Furthermore, as previously described for Eyg, a reduction in the amount of HP1a in the eye imaginal disc derepresses wg. Together, our results suggest a model in which Eyg specifically binds to the wg enhancer region, recruiting HP1a to that site. The recruitment of HP1a prevents transcription by favoring a closed, heterochromatin-like structure. Thus, for the first time, we show that HP1a plays a direct role in the repression of a developmentally regulated gene, wg, during Drosophila eye development.

Dampening the Signals Transduced through Hedgehog via MicroRNA miR-7 Facilitates Notch-Induced Tumourigenesis

“…Thus, boi is negatively regulated by Notch's organizer activity or it at least reflects this activity negatively. Since Eyg encodes a transcriptional repressor [14],[15], it may directly repress boi transcription. This Hh co-receptor does contain a consensus Eyg-binding site for repression (TCACTGA [14]) at position chrX: 2.359.784, although we could not validate the direct binding of Eyg to the boi promoter region by chromatin immunoprecipitation (unpublished data).…”

“…A similar DV organizer has been found in a variety of contexts, including the fly and vertebrate limbs, although the expression of eyg is restricted to the fly eye. Eyg is functionally related to the human PAX6(5a) oncogene [13] and acts as a transcriptional repressor [14],[15] though complementary patterns of expression of the organizer in developing eyes have never been reported.…”

Linker histone dH1K27 dimethylation marks Drosophila heterochromatin independently of H3K9 methylation

“…We found that dH1K27me2 regions are statistically enriched in several TFs binding motifs, some of which have been reported to associate with pericentromeric heterochromatin, such as GAGA factor and the PAX family TF eyegone (eyg) (36,37). While the presence of TEs and repeated sequences was expected, the presence of TF binding motifs was somehow surprising.…”

The TALE Transcription Factor Homothorax Functions to Assemble Heterochromatin during Drosophila Embryogenesis

“…We have identified the transcription factor Hth as one of the key factors for transcription-dependent heterochromatin formation throughout embryonic development in Drosophila . A function of transcription factors in heterochromatin formation was first described by our group in Drosophila [ 5 , 7 ], and later confirmed in mouse culture cells [ 6 ]. Hth mutants show overall reduced levels of H3K9me3 and de-condensation of all the constitutive heterochromatin structures analysed.…”

“…However, very little is known about the regulation of this non-coding RNA transcription and its phenotypic outcome in a developing organism. Work done in mouse cells and in Drosophila clearly shows that specific transcription factors are involved in the formation of heterochromatin [ 5 – 7 ].…”