Conservation of HP1 and methylated H3 histones as heterochromatic epigenetic markers in the holocentric chromosomes of the cabbage moth, Mamestra brassicae (Lepidoptera)

Abstract

Abstract. The methylated H3 histone and heterochromatin protein 1 (HP1) are markers of heterochromatin in several eukaryotes possessing monocentric chromosomes. In order to confirm that these epigenetic markers of heterochromatin are evolutionary conserved, the distribution of methylated H3 histones and HP1 homologues on the holocentric chromosomes of the cabbage moth Mamestra brassicae (Lepidoptera) were studied. In particular, PCR experiments with degenerated primers identified a HP1 homologue (called MbHP1) in the M. brassicae genome. Sequencing showed that the MbHP1 gene is 737 bp long including a 102 bp 5'UTR and a 635 bp coding portion (comprising an 80 bp intron). The MbHP1 peptide consisted of 184 amino acids, had a 20 kDa molecular mass and a net negative charge. At the structural level, it showed an N terminal chromo-domain and a chromo-shadow--domain at the C terminus linked by a short hinge region. At the cytogenetic level, MbHP1 was located exclusively in the heterochromatic regions of the chromosomes. The same heterochromatic regions became labelled after immuno-staining with antibodies against H3 histone methylated at lysine 9, reinforcing the hypothesis that this modified histone is essential for HP1 binding. Our data, as a whole, confirm that heterochromatic components and markers are evolutionary conserved both in mono-and holocentric chromosomes despite the difference in the distribution of heterochromatin on chromosomes.

Analysis of heterochromatic epigenetic markers in the holocentric chromosomes of the aphid Acyrthosiphon pisum

“…In the lane containing the protein extract from SL2 Drosophila cells, the HP1 antibody, as expected, recognized an antigen with an apparent molecular weight of 34 kDa (Eissenberg & Elgin 2000) ( Figure 3, left). In the lane containing the whole-protein extract from M. brassicae cells, a single band of about 20 kDa was observed, as expected on the basis of the data reported by Borsatti & Mandrioli (2005) (Figure 3, centre). In the lane containing the protein extract from aphid tissues, the antibody recognized a single protein with an approximate weight of 28 kDa that is coherent with the estimated weight of the predicted ApHP1 peptide (Figure 3, right).…”

“…In view of this, immunodetection of HP1 and Me9H3 was performed, indicating that aphid constitutive heterochromatin is enriched both in H3 histone monomethylated at lysine 9 and in HP1 proteins. These epigenetic markers are, therefore, true heterochromatic markers not only for vertebrate chromosomes but also for insect heterochromatin, as previously reported in the dipteran D. melanogaster (Cowell et al 2002), in the homopteran P. citri (Cowell et al 2002) and in the lepidopteran M. brassicae (Borsatti & Mandrioli 2005).…”

“…Nevertheless, the occurrence of epigenetic chromatin modifications in aphid heterochromatin has been neglected. The same is also true for most of the other insect species possessing holocentric chromosomes, since at present the occurrence and functions of heterochromatic epigenetic markers have been studied only in the coccid Planococcus citri and in the moth Mamestra brassicae (Field et al 2004, Borsatti & Mandrioli 2005.…”

The cytogenetic architecture of the aphid genome

“…Thus, H3 histone monomethylated at lysine 9 and HP1 are common epigenetic markers for heterochromatin, both in vertebrates and invertebrates (e.g. Jacobs et al, 2001;Lachner et al, 2001;Cowell et al, 2002;Borsatti & Mandrioli, 2005). Both in A. pisum (Mandrioli & Borsatti, 2007) and A. nerii (Mandrioli et al, 2011), the only aphid species to date studied at the epigenetic level, Me9H3 and HP1 have been localized in C-positive areas indicating that aphid C-heterochromatin is enriched in both of these epigenetic markers.…”

H3K9me2 genome-wide distribution in the holocentric insect Spodoptera frugiperda (Lepidoptera: Noctuidae)

“…More importantly H3K9me2 signal surrounding centromeres is thought to be lost in these organisms, unlike holocentric C.elegans (Steiner et Henikoff 2014). Previous studies conducted on Lepidopteran showed nonetheless that H3K9me2 is still associated to repeated DNA at rDNA loci and sexual chromosomes (Stanojcic et al 2011; Borsatti et Mandrioli 2013).…”