# E(var)3–9 protein in Drosophila ovaries represses telomeric retrotransposons, mutant embryos die

- Published: 2026-11-15 11:26 UTC
- Section: Life & Health › Biology & biochemistry
- Tags: E(var)3–9, Drosophila ovaries, heterochromatin, telomeric retrotransposons, HeT-A, Telomere Cluster, H3K9me3, ChIP-seq, piRNA pathway, Polo kinase
- URL: https://realtech.media/news/rt-3833f4113f1afb8869556847_e_var_3/

**In Drosophila ovaries, E(var)3–9 represses telomeric retrotransposons and supports large heterochromatic genes; without it, embryos of mutant mothers die.**

![E(var)3–9 protein in Drosophila ovaries represses telomeric retrotransposons, mutant embryos die](https://realtech.media/media/2026/11/abf3c554075a33a3.jpg)
*Polychronis Rempoulakis, Wikimedia Commons, CC BY-SA 4.0*

A team led by Alla Kalmykova and colleagues studied the zinc-finger chromatin protein Enhancer of variegation 3–9, E(var)3–9, in Drosophila ovaries. According to the paper in Epigenetics & Chromatin (doi.org/10.1186/s13072-026-00712-y), the protein represses telomeric retrotransposons and promotes transcription of large protein-coding genes embedded in heterochromatin [1]. The work was done in fruit flies, using a newly generated, presumably null mutation.

Heterochromatin is not a uniformly repressive and compact region: genes and repeats within it are transcribed. E(var)3–9 is little studied and promotes expression of genes placed in the heterochromatin environment. Its mutations cause female sterility, which suggests a role in oogenesis and early embryogenesis [1].

## Localization and gene expression

In the ovaries, E(var)3–9 is enriched in heterochromatic regions of the nurse cells, including a heterochromatic domain associated with the fourth chromosome and clustered telomeres [1]. Chromatin immunoprecipitation and sequencing (ChIP-seq) showed that the protein is abundant in the main heterochromatic regions, which are also enriched in trimethylated histone H3 at lysine 9 (H3K9me3) [1].

Chromatin-associated RNA sequencing of mutant ovaries, compared with wild type, showed specific upregulation of telomeric retrotransposons and downregulation of the large protein-coding genes embedded within heterochromatin [1]. Chromatin-associated and small RNA sequencing also suggested that the mutations do not affect the piRNA pathway [1].

## Consequences for embryos

Fluorescent in situ RNA hybridization showed that HeT-A transcripts in the mutants are mostly associated with the Telomere CLuster (TCL) [1]. Overexpression of HeT-A in mutant ovaries led to aggregation of HeT-A RNA and HeT-A Gag protein around the centrosomes of early embryos, with severe abnormalities in the distribution of Polo kinase [1]. Embryos from mutant mothers showed mitotic defects and chromosome mis-segregation, resulting in embryonic lethality [1].

The authors describe a dual regulation against harmful overexpression of telomeric retrotransposons. Telomeres that are not clustered and lie in euchromatin are controlled by the RNA-binding protein Ars2 and the piRNA pathway, whereas retrotransposon expression in the heterochromatic TCL is downregulated by E(var)3–9 [1].

## Sources

1. [doi.org](https://doi.org/10.1186/s13072-026-00712-y)
2. [bioengineer.org](https://bioengineer.org/drosophila-chromatin-protein-regulates-telomeric-repeats-and-heterochromatic-genes)

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Source: RealTech, realtech.media — https://realtech.media/news/rt-3833f4113f1afb8869556847_e_var_3/