Sex chromosome composition revealed in Characidium fishes (Characiformes: Crenuchidae) by molecular cytogenetic methods

Abstract

The W chromosome of the fishes Characidium cf. fasciatum, Characidium sp. and Characidium cf. gomesi is heterochromatic, as is usually seen in most Characidium species. Samples of W-chromatin were collected by mechanical microdissection and amplified by DOP-PCR (degenerate oligonucleotide-primed polymerase chain reaction), to be used as painting probes (DCg and CgW) and for sequence analysis. FISH (fluorescence in situ hybridization) with DCg probe painted the whole W chromosome, the pericentromeric region of Z chromosomes and the terminal region of B chromosomes. DOP-PCR-generated fragments were cloned, sequenced and tested by in situ hybridization, but only CgW4 produced positive hybridization signals. Clone sequence analysis recovered seven distinct sequences, of which six did not reveal any similarity to other known sequences in the GenBank or GIRI databases. Only CgW9 clone sequence was recognized as probably derived from a Helitron-transposon similar to that found in the genome of the zebrafish Danio rerio. Our results show that the composition of Characidium's W chromosome does seem rich in repetitive sequences as well as other W chromosomes found in several species with a ZW sex-determining mechanism.

The karyotypes and evolution of ZZ/ZW sex chromosomes in the genus Characidium (Characiformes, Crenuchidae)

“… fasciatum Reinhardt, 1867 (Table 1 ), but it is also present in most Characidium species studied. The sex chromosomes in Characidium show a high degree of differentiation among species by chromosomal size, morphology, heterochromatin accumulation and presence or absence of rDNA sites ( Maistro et al 1998 , 2004 , Centofante et al 2001 , 2003 , Vicari et al 2008 , Noleto et al 2009 , Pansonato-Alves et al 2010 , 2011b , 2014 , Machado et al 2011 , Pazian et al 2013 , 2014 , Pucci et al 2014 , 2016 , Scacchetti et al 2015a , 2015b , 2015c , Serrano et al 2017 ), as exemplified in Fig. 3 .…”

“…aff. C. vidali displayed similar repetitive DNA sequences among B and sex chromosomes ( Pansonato-Alves et al 2014 , Pazian et al 2014 , Scacchetti et al 2015a , Serrano et al 2016 ), while Characidium oiticicai Travassos, 1967 and C. alipioi did not show such shared sequences ( Pansonato-Alves et al 2014 , Serrano et al 2017 , respectively). Despite their molecular homology, it was demonstrated that B and W chromosomes do not form multivalent pairings during meiosis in male and female C. gomesi individuals.…”

“…W-specific repetitive probes were already constructed for Characidium using microdissection from female metaphase chromosomes and degenerate oligonucleotide-primed PCR ( DOP-PCR ) or whole genome amplification ( WGA ) protocols. These probes were later applied to chromosome painting in Characidium using a C. gomesi W-specific probe ( Machado et al 2011 , Pazian et al 2013 , 2014 , Pansonato-Alves et al 2014 , Pucci et al 2014 ). This was followed by investigations of homologous regions between the sex pairs, B chromosomes and autosomes ( Machado et al 2011 , Pazian et al 2013 , 2014 , Pansonato-Alves et al 2014 , Pucci et al 2014 , 2016 , Scacchetti et al 2015a , 2015b , Serrano et al 2016 , 2017 ), and the cloning of a W-specific sequence that generated the CgW9 clone, which is similar to the zebrafish Helitron transposon ( Pazian et al 2014 ).…”