In situ hybridization of bat chromosomes with human (TTAGGG)n probe, after previous digestion with Alu I

Karina De Cassia Faria,Eliana Morielle-Versute

doi:10.1590/s1415-47572002000400003

Abstract

The purpose of this work was to verify the ability of the enzyme Alu I to cleave and/or remove satellite DNA sequences from heterochromatic regions in chromosomes of bats, by identifying the occurrence of modifications in the pattern of fluorescence in situ hybridization with telomeric DNA. The localization and fluorescence intensity of the telomeric DNA sites of the Alu-digested and undigested chromosomes of species Eumops glaucinus, Carollia perspicillata, and Platyrrhinus lineatus were analyzed. Telomeric sequences were detected at the termini of chromosomes of all three species, although, in C. perspicillata, the signals were very faint or absent in most chromosomes. This finding was interpreted as being due to a reduced number of copies of the telomeric repeat, resulting from extensive telomeric association and/or rearrangements undergone by the chromosomes of Carollia. Fluorescent signals were also observed in centromeric and pericentromeric regions in several two-arm chromosomes of E. glaucinus and C. perspicillata. In E. glaucinus and P. lineatus, some interstitial and terminal telomeric sites were observed to be in association with regions of constitutive heterochromatin and ribosomal DNA (NORs). After digestion, these telomeric sites showed a significant decrease in signal intensity, indicating that enzyme Alu I cleaves and/or removes part of the satellite DNA present in these regions. These results suggest that the telomeric sequence is a component of the heterochromatin, and that the C-band- positive regions of bat chromosomes have a different DNA composition.

Highlights

The telomeres of chromosomes are composed by specific tandem repeats of the DNA sequence (TTAGGG)n that are conserved in all species of vertebrates (Meyne et al, 1989, 1990)
In the Fluorescence in situ hybridization (FISH) experiments with a telomeric probe, the chromosomes of E. glaucinus which had not been previously treated with the enzyme exhibited telomeric sequences at the termini of the chromosomes
Several studies have attempted to characterize the heterochromatic bands, showing that the areas of constitutive heterochromatin identified after C-banding correspond to satellite DNA regions (Pieczarka and Mattevi, 1998; Hennig, 1999; Ventura et al, 2001)

Summary

Introduction

The telomeres of chromosomes are composed by specific tandem repeats of the DNA sequence (TTAGGG)n that are conserved in all species of vertebrates (Meyne et al, 1989, 1990) This repeated sequence has been detected in telomeres, and in interstitial and centromeric chromosomal regions, in a variety of vertebrate species; in almost all of them, it is coincident with positive C-bands (Meyne et al, 1989, 1990; Abuín et al, 1996; Vermeesch et al, 1996; Garagna et al, 1995; Ono and Yoshida 1997; Sharma and Sharma, 1998; Go et al, 2000; Pagnozzi et al, 2000). The REs induce structural alterations in metaphase chromosomes which could be related, at the cytological level, to specific structural characteristics of eukaryote chromosome bands, reflecting a distribution of different DNA sequences along the chromosomes (Fernandez et al, 1998; Garcia et al, 1999)

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