Date Published: January 27, 2017
Publisher: Public Library of Science
Author(s): Michelly da Silva dos Santos, Rafael Kretschmer, Carolina Frankl-Vilches, Antje Bakker, Manfred Gahr, Patricia C. M. O´Brien, Malcolm A. Ferguson-Smith, Edivaldo H. C. de Oliveira, Johan J Bolhuis.
Songbird species (order Passeriformes, suborder Oscines) are important models in various experimental fields spanning behavioural genomics to neurobiology. Although the genomes of some songbird species were sequenced recently, the chromosomal organization of these species is mostly unknown. Here we focused on the two most studied songbird species in neuroscience, the zebra finch (Taeniopygia guttata) and the canary (Serinus canaria). In order to clarify these issues and also to integrate chromosome data with their assembled genomes, we used classical and molecular cytogenetics in both zebra finch and canary to define their chromosomal homology, localization of heterochromatic blocks and distribution of rDNA clusters. We confirmed the same diploid number (2n = 80) in both species, as previously reported. FISH experiments confirmed the occurrence of multiple paracentric and pericentric inversions previously found in other species of Passeriformes, providing a cytogenetic signature for this order, and corroborating data from in silico analyses. Additionally, compared to other Passeriformes, we detected differences in the zebra finch karyotype concerning the morphology of some chromosomes, in the distribution of 5S rDNA clusters, and an inversion in chromosome 1.
Species belonging to the suborder Oscines (Aves, order Passeriformes), also known as songbirds, have been employed as models in studies concerning neuroscience, vocal communication, development, behavioural genomics, ecology and evolution, among others [1–7]. Among songbirds, the zebra finch (Taeniopygia guttata, TGU) and the canary (Serinus canaria, SCA) belong to different families (Estrildidae and Fringillidae, respectively), are frequently used and have recently been the subjects of genomic analyses [8–11]. They are originally from different zoogeographical regions–the zebra finch is an Australian species, while the canary originates from the Canary Islands, located just off the southern coast of Africa .
The genome sequencing of an increasing number of birds, combined with cytogenomic mapping is helping to diminish the discrepancy of information concerning avian genomic organization in comparison to other Vertebrate groups. Additionally, the agreement between the data obtained by in silico assembling and FISH approaches show that these metholologies are complementary and may be used in combination to generate cytogenetic markers, or to provide information not easily obtained by sequencing and genomic assembling, such as the localization of repetitive sequences, as for example 5S and 18S rDNA clusters. Hence, a complete karyotypical characterization–including the distribution of heterochromatic blocks and rDNA blocks–may be important to complete the interpretation of data obtained by sequencing. A clear example of this is the fact that, because of the peculiar nature of the avian karyotype, the number of syntenic groups generated by bioinformatic approaches are not accurate, and usually do not match with the actual diploid number .