Chromosomal painting and ZW sex chromosomes differentiation in Characidium (Characiformes, Crenuchidae)

• Published in: BMC genetics Vol. 12; no. 1; p. 65
• Main Authors: Machado, Tatiana C, Pansonato-Alves, José C, Pucci, Marcela B, Nogaroto, Viviane, Almeida, Mara C, Oliveira, Claudio, Foresti, Fausto, Bertollo, Luiz A C, Moreira-Filho, Orlando, Artoni, Roberto F, Vicari, Marcelo R
• Format: Journal Article
• Language: English
• Published: England BioMed Central Ltd 25.07.2011; BioMed Central; BMC
• Subjects: Analysis; Animals; Biological Evolution; Characiformes; Chromosome Painting; Female; Fishes - genetics; Genetic aspects; Karyotyping; Phylogeny; Physiological aspects; Population ecology; Sex Chromosomes; Sex Differentiation; Brazil
• ISSN: 1471-2156; 1471-2156
• DOI: 10.1186/1471-2156-12-65

The Characidium (a Neotropical fish group) have a conserved diploid number (2n = 50), but show remarkable differences among species and populations in relation to sex chromosome systems and location of nucleolus organizer regions (NOR). In this study, we isolated a W-specific probe for the Characidium and characterized six Characidium species/populations using cytogenetic procedures. We analyzed the origin and differentiation of sex and NOR-bearing chromosomes by chromosome painting in populations of Characidium to reveal their evolution, phylogeny, and biogeography. A W-specific probe for efficient chromosome painting was isolated by microdissection and degenerate oligonucleotide primed-polymerase chain reaction (DOP-PCR) amplification of W chromosomes from C. gomesi. The W probe generated weak signals dispersed on the proto sex chromosomes in C. zebra, dispersed signals in both W and Z chromosomes in C. lauroi and, in C. gomesi populations revealed a proximal site on the long arms of the Z chromosome and the entire W chromosome. All populations showed small terminal W probe sites in some autosomes. The 18S rDNA revealed distinctive patterns for each analyzed species/population with regard to proto sex chromosome, sex chromosome pair, and autosome location. The results from dual-color fluorescence in situ hybridization (dual-color FISH) using W and 18S rDNA probes allowed us to infer the putative evolutionary pathways for the differentiation of sex chromosomes and NORs, from structural rearrangements in a sex proto-chromosome, followed by gene erosion and heterochromatin amplification, morphological differentiation of the sex chromosomal pair, and NOR transposition, giving rise to the distinctive patterns observed among species/populations of Characidium. Biogeographic isolation and differentiation of sex chromosomes seem to have played a major role in the speciation process in this group of fish.