Abstract
Chromatin organization in the holocentric chromosomes of the green apple aphid Aphis pomi has been investigated at a cytological level after C-banding, NOR, Giemsa, fluorochrome staining and fluorescent in situ hybridization (FISH). C-banding technique showed that heterochromatic bands are exclusively located on X chromosomes. This data represents a peculiar feature that clearly contradicts the equilocal distribution of heterochromatin typical of monocentric chromosomes. Moreover, silver staining and FISH carried out with a 28S rDNA probe localized rDNA genes on one telomere of each X chromosome; CMA3 staining reveals that these silver positive telomeres are the only GC-rich regions among A. pomi heterochromatin, whereas all other C-positive bands are DAPI positive thus containing AT-rich DNA.
Highlights
To date, almost all studies concerning chromatin structure and organization have been focused on monocentric chromosomes whereas data regarding holocentric ones have been neglected
This work is aimed to search for the localization and the DNA composition of heterochromatin in the holocentric chromosome of the green apple aphid Aphis pomi a small yellow-green aphids widely distributed in Europe, Middle East, throughout North America
Giemsa staining of C-banded chromosomes put in evidence four heterochromatic bands limited to the X chromosomes both at telomeric and interstitial sites, whereas autosomes lack any kind of differential staining (Figure 2(a))
Summary
Almost all studies concerning chromatin structure and organization have been focused on monocentric chromosomes whereas data regarding holocentric ones have been neglected. These chromosomes are termed holokinetic because, during mitotic anaphase, they behave as if the spindle attachment is not localized, so that chromatids move apart in parallel and do not form the classical V shaped figures usually observed during the movement of monocentric ones (Blackman, 1987). The identification of chromosomal markers in organisms possessing holocentric chromosomes is extremely important since the lack of a primary conscription together with the difficult in obtaining a clear-cut banding pattern have greatly hampered cytogenetic studies in species possessing such a peculiar chromatin organization (Blackman 1987, Hales et al, 1997, Manicardi et al, 2002). Green apple aphids are important indirect pests of apple that require monitoring and, often, insecticide treatments (Carroll & Hoyt, 1984, Pfeier, Brown & Varn 1989)
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