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

Abstract

We have previously identified Homothorax (Hth) as an important factor for the correct assembly of the pericentromeric heterochromatin during the first fast syncytial divisions of the Drosophila embryo. Here we have extended our studies to later stages of embryonic development. We were able to show that hth mutants exhibit a drastic overall reduction in the tri-methylation of H3 in Lys9, with no reduction of the previous di-methylation. One phenotypic outcome of such a reduction is a genome instability visualized by the many DNA breaks observed in the mutant nuclei. Moreover, loss of Hth leads to the opening of closed heterochromatic regions, including the rDNA genomic region. Our data show that the satellite repeats get transcribed in wild type embryos and that this transcription depends on the presence of Hth, which binds to them as well as to the rDNA region. This work indicates that there is an important role of transcription of non-coding RNAs for constitutive heterochromatin assembly in the Drosophila embryo, and suggests that Hth plays an important role in this process.

Histone H3 Dynamics Reveal Domains with Distinct Proliferation Potential in the Arabidopsis Root

“…For example, the last cell cycle during synchronized divisions of the Drosophila melanogaster embryo can be distinguished from the previous ones by several features, including increased cell cycle duration (with an extended G2) (Yuan et al, 2014;Blythe and Wieschaus, 2015;Zaballos et al, 2015). We believe that an analogous scenario may apply to the RAM during the last cell cycle just before cell proliferation arrest and initiation of differentiation, associated with changes in the gene expression program.…”

A function of Spalt proteins in heterochromatin organization and maintenance of genomic DNA integrity

“…In addition, the appearance of mitotic defects, increased expression of retrotransposons and alterations in H3 phosphorylation observed in early blastoderms derived from sal heterozygous flies suggest a role for Salm/Salr in the initial establishment of centromeric heterochromatin regions. Other Drosophila transcription factors, such as Eyegone (Eyg) and Homothorax (Hth) have been shown to participate in the regulation of heterochromatic assembly in early Drosophila blastoderms (Hth; Salvany et al, 2009; Zaballos et al, 2015) or in heterochromatic gene silencing (Eyg; Salvany et al, 2012; Blom-Dahl and Azpiazu, 2018). In the case of Hth, it has been proposed that maternal Hth contributes to the transcription of satellite repeats, whereas Eyg interacts with HP1 to maintain a closed heterochromatin-like conformation (Salvany et al 2012, 2009).…”