The mobile nature of acrocentric elements illustrated by three unusual chromosome variants

Abstract

Variant chromosomes are polymorphic in areas that are rich in repeat sequences such as the pericentromeric regions or in the acrocentric short arm regions. The dynamic nature of these regions is evident in the polymorphisms they exhibit. In this paper three unusual variants are described: a chromosome 21 with additional material on its short arm, a chromosome 7 with an insertion in the short arm and a chromosome 2 with satellites at the end of the long arm. All three variants were shown to involve acrocentric elements using special banding techniques and fluorescence in situ hybridization. The 21 variant was found to be a tricentric with a 21 and two 15 alpha-, two classical and three acrocentric beta-satellite signals interspersed by AgNOR-positive regions. The telomeres were present at the two terminal ends. The insertion on chromosome 7 was found to be C-band positive and to contain acrocentric beta-satellite DNA. However, acrocentric alpha-satellite, classical satellite, whole-chromosome-painting or all-telomeres sequence probes did not hybridize to the insertion. The satellited region of chromosome 2 had two C-bands, a small positive all-centromeres probe signal, and two signals for the beta-satellite probe. Sandwiched between the beta-satellite sequences was an AgNOR-positive region. The telomeres were present at the two ends of the satellited chromosome 2. Chromosome 2 subtelomeric probes hybridized to the terminal ends of the short and long arm of chromosome 2. The common thread in these three variants is the involvement of acrocentric short arm elements. The acrocentric short arm elements are shown to move to other acrocentric or nonacrocentric chromosomes and relocate to both terminal and interstitial positions. The integrations are stable and heritable.

Repetitive sequences originating from the centromere constitute large-scale heterochromatin in the telomere region in the siamang, a small ape

“…In the family Hominidae, in addition to occurring in the centromeric heterochromatin, alpha satellite DNA occurs in some interstitial regions, which are thought to be remnants of once-functional centromeres (Reddy and Sulcova, 1998). To our knowledge, however, alpha satellite DNA has not been found in telomere regions in Hominidae.…”

Chromosome abnormalities without phenotypic consequences

“…It was observed in a fetus and 2 normal individuals of the same family: father and grandfather (Miller et al 1995). Interstitially satellited chromosomes were reported by Reddy and Sulcova (1998): chromosome 21 with additional material on its short arm, chromosome 7 with NOR insertion in the p arm, and chromosome 2 with satellites at the end of the q arm. A case of interstitially satellited 6ps chromosome was reported by Chen et al (2004).…”

A New Multicolor Fluorescence In Situ Hybridization Probe Set Directed Against Human Heterochromatin

“…HCM-FISH showed in one step that this material was derived from an acrocentric short arm, once with and once without the NOR region. Similar reports are scarcely available in the literature (Watt et al 1984;Reddy and Sulcova 1998;Guttenbach et al 1998;Chen et al 2004). However, even such an insertion in an X chromosome was seen once (Tamagaki et al 2000).…”