Cytogenetic and molecular characterization of a highly repeated DNA sequence in the peach potato aphid Myzus persicae

Abstract

Electrophoresis following digestion of Myzus persicae genomic DNA with HindIII showed the presence of a prominent band of approximately 200 bp whereas a faint electrophoretic band corresponding to DNA fragments of about 3000 bp was observed after digestion with ApaI. In situ digestion with restriction enzymes, followed by in situ nick translation, showed that ApaI targets are localized at the nucleolus organizer-bearing X telomeric region, whereas HindIII restriction sites are clustered in intercalary C-positive areas on the same X chromosome. Fluorescent in situ hybridization (FISH) carried out by using digoxygenin-labeled HindIII repeats as probe fully confirmed overlapping between the hybridization sites of this probe and the AT-rich intercalary heterochromatic bands on the X chromosome. These findings, together with published data, allow us to conclude that the M. persicae genome possesses three classes of C-positive heterochromatin: (i) a GC-rich argentophilic band located on one telomere of the X chromosome that contains ApaI targets; (ii) AT-rich intercalary bands located on the X chromosome containing clustered HindIII fragments; (iii) AT-rich telomeric bands located on autosomes, consisting of HaeIII repeats. Molecular analysis has shown that the length of the HindIII repeat consensus sequence is 189 bp with an AT content of 67%. Southern blotting with HindIII monomers revealed a regular ladder of bands composed of multimers of basic length that are characteristic of satellite DNAs. The HindIII repeat displays other features typical of eukaryotic satellite arrays such as overlapping with heterochromatic bands and a high degree of sequence similarity among monomers (84%-94%). A similarity plot showed that sequences were particularly variable in the 50-100 bp region whereas they proved to be highly conservative in the first 50 bp, thus suggesting that this portion of the repeat might be functionally important.

Meiosis and fluorescent banding in Edessa meditabunda and E. rufomarginata (Heteroptera: Pentatomidae: Edessinae)

“…The conspicuous CMA bright band detected at the telo meric region of the largest autosomal bivalent in E. meditabunda together with the fact that the nucleolus, as revealed by silver staining, was associated with the telo meric region of this bivalent, led us to conclude that the NOR region is associated with a GC rich band. This cor respondence between CMA positive banding and NOR regions has also been described in the X chromosome of aphids Mandrioli et al, 1999). In the present contribution the DAPI and CMA bright fluo rescence of the sex chromosomes of E. meditabunda and E. rufomarginata until diplotene is consistent with the allocycly of these chromosomes during male meiosis, and it probably reflects different degrees of chromatin con densation rather than differences in base composition.…”

Patterns of heterochromatin distribution in plant chromosomes

“…In several species of Rhynchospora, Vanzela et al (1998) observed the occurrence of multiple rDNA sites always distributed in the terminal regions. Similarly, satellite DNA sequences with generalized equilocal distribution were observed in the holocentric chromosomes of the peach potato aphid (Spence et al, 1998;Mandrioli et al, 1999). Therefore, HC equidistribution may not depend fundamentally on Rabl orientation and band-centromere distance, but rather on some structural or functional similarity of each chromosomal region that makes them equally receptive to the installation and/or amplification of the same or similar DNA sequence (Fry and Salser, 1977;Flavell, 1982).…”

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

“…The heterochromatin of holocentric chromosomes, therefore, shows several common features with that of monocentric chromosomes since both contain ATrich satellite DNAs, transposable elements, HP1 proteins and methylated histones (e.g. Ohbayashi et al, 1998;Mandrioli et al, 1999;Cowell et al, 2002;Mandrioli, 2002;Mandrioli, 2003a, b;Mandrioli et al, 2003).…”