Karyotype analysis of Fringilla coelebs (Aves, Passeriformes) using fluorochrome staining, Ag-NOR and FISH

Svetlana Derjusheva, Anna Kurganova, Alsu Saifitdinova and Elena Gaginskaya
Biological Institute of Saint-Petersburg University, Saint-Petersburg, 198504 RUSSIA

Chromosome complements of various passerine species are similar in the chromosome numbers and morphology. On the other hand, a deep divergence between Passeriformes and other birds manifests itself in chromosomal rearrangements. Fringilla coelebs, widely distributed in the world species, is a typical representative of the order Passeriformes. So the chaffinch may serve as a model species to study the origin, evolution and structural organization of passerine chromosomes.

Karyotype

The karyotype of F.coelebs (2n=80) consists of 7 pairs of biarmed macrochromosomes: 6 autosome pairs, Z and W. The rest chromosomes are microchromosomes. Three pairs of largest microchromosomes are easily determined and acrocentric.

CMA3/DAPI stained metaphase chromosomes
Enlarge in new window (38K)

Metaphase chromosomes obtained from fibroblast culture are stained by Chromomycin A3 (CMA3) and DAPI simultaneously. Centromeric heterochromatin of each chromosome was found to be GC-enriched (green). Euchromatin arms of macrochromosomes are generally CMA-negative (blue). As to microchromosomes, they are either GC-enriched or AT-enriched.

Macrochromosome idiograms
Enlarge in new window (15K)

R-banded macrochromosome idiograms created accordingly with computer measument of CMA-stained metaphase spreads.

NOR-bearing chromosmes

rDNA localization
Enlarge in new window (37K)

rRNA loci are localized on a pair of miccrochromosomes (arrows) by FISH with Xenopus 18S+28S rDNA probe. FITC/PI

rDNA localization
Enlarge in new window (45K)

Ag-staining also revealed a pair of NOR-bearing chromosomes (arrows).

The results demonstrate that in Fringilla coelebs chromosome set the NOR location is typical of bird karyotype.

The localization of (TTAGGG)n in chaffinch chromosomes

It is well known that in addition to terminal sites of (TTAGGG)n telomeric repeat there are chromosome interstitial sites of that, their origin being a subject of discussion (Meyne et al., 1990; Nanda & Schmid, 1994). Comparative analysis of TTAGGG sites distribution may provide understanding of chromosomal reorganization during karyotype evolution.

FISH with telomeric probe
Enlarge in new window (61K)

FISH on chaffinch metaphase chromosomes using human telomeric repeat as a probe. Cy3/ CMA3.

In the chaffinch interstitial (TTAGGG)n sites are revealed on all macrochromosomes.

Selected chromosomes with telomeric probe
Enlarge in new window (49K)

Selected macrochromosomes 1 to 6 and ZW sex chromosomes of the chaffinch after FISH with (TTAGGG)n probe. On the left - CMA3; on the right - Cy3/CMA3.

It is worthy to remark that in total the chaffinch chromosomes contain more interstitial TTAGGG sites revealed by FISH as compared with species from other avian orders, most of the interstitial sites being out of pericentromeric regions. It may reflect the evolutionary status of Passeriformes.

The karyotype of the chaffinch was previously described by Piccini & Stella (1970), but only in routine staining. Here, fluorescent chromosome banding, NOR detection by FISH and Ag-staining, and the distribution of telomeric TTAGGG repeat in metaphase chromosomes are presented for the first time.

References

Meyne J. et al. (1990) Chromosoma 99: 3–10.
Nanda I. & Schmid M. (1994) Cytogenet. Cell Genet. 65: 190–193.
Piccini E. & Stella M. (1970) Caryologia 23: 189–202.

© Laboratory of Chromosome Structure and Function, 2001