Mezzasalma, M., F. Andreone, F. Glaw, G. Odierna, A. Petraccioli & F. M. Guarino

Chromosome aneupolyploidy in an endemic Malagasy gecko (Gekkonidae: Geckolepis). pp. 56-62.

Abstract. Polyploidy is exceptional in mammals and rare in reptiles. Unscheduled polyploidy often leads to cell disorders and cancer through genomic rearrangements that can be difficult to trace and is particularly poorly studied in non-model vertebrates. In the present paper, using a combination of banding and Fluorescence In Situ Hybridization (FISH) techniques, we reconstruct and characterize the origin and significance of aneupolyploid karyotypes found in the bone marrow of an individual of the Malagasy gecko Geckolepis typica. Our results demonstrate that these anomalous karyotypes correspond to a proliferative cell disorder characterized by a succession of distinct structural events, from a preliminary duplication of the whole genome to the instability of loci of NORs and subsequent chromosome rearrangements that will produce aneuploid cells. Our comparison between the newly described normal, i.e., diploid, karyotype of the species (2n = 40) and aneutetraploid plates (4n = 77–80) revealed that translocations of NOR-bearing chromosomes are involved in generating aneuploidy. Furthermore, simultaneous and multiple translocations of the NOR-bearing chromosomes occurred with relatively high frequency (27% and 19%, respectively) on distinct chromosome pairs. In addition, in about 9% of 90 scored metaphase plates, structural instability of the NOR regions also produced detachments of rDNA arrays and generated an accessory, fully heterochromatic B-chromosome. Our data suggest that the duplication of the whole genome can be considered a preliminary stage in proliferative cell disorders, inducing chromosomal instability and structural rearrangements.

Key words. Squamata, aneuploidy, chromosome rearrangements, NORs, genetic disorder, B-chromosome, Madagascar.