Major and minor U small nuclear RNAs genes characterization in a neotropical fish genome: Chromosomal remodeling and repeat units dispersion in Parodontidae.

In association with many proteins, small nuclear RNAs (snRNAs) organize the spliceosomes that play a significant role in processing precursor mRNAs during gene expression. According to snRNAs genic arrangements, two kinds of spliceosomes (major and minor) can be organized into eukaryotic cells. Although in situ localization of U1 and U2 snDNAs have been performed in fish karyotypes, studies with genomic characterization and functionality of U snRNAs integrated into chromosomal changes on Teleostei are still scarce. This study aimed to achieve a genomic characterization of the U snRNAs genes in Apareiodon sp. (2n = 54, ZZ/ZW), apply these data to recognize functional/defective copies, and map chromosomal changes involving snDNAs in Parodontidae species karyotype diversification. Nine snRNA multigene families (U1, U2, U4, U5, U6, U11, U12, U4atac and U6atac) arranged in putatively functional copies in the genome were analyzed. Proximal Sequence Elements (PSE) and TATA-box promoters occurrence, besides an entire transcribed region and conserved secondary structures, qualify them for spliceosome activity. In addition, several defective copies or pseudogenes were identified for the snRNAs that make up the major spliceosome. In situ localization of snDNAs in five species of Parodontidae demonstrated that U1, U2, and U4 snDNAs were involved in chromosomal location changes or units dispersion. The U snRNAs defective/pseudogenes units dispersion could be favored by the probable occurrence of active retrotransposition enzymes in the Apareiodon genome. The U2 and U4 snDNAs sites were involved in independent events in the differentiation of sex chromosomes among Parodontidae lineages. The study characterized U snRNA genes that compose major and minor spliceosomes in the Apareiodon sp. genome and proposes that their defective copies trigger chromosome differentiation and diversification events in Parodontidae.

Comparative cytogenetics among Leporinusfriderici and Leporellusvittatus populations (Characiformes, Anostomidae): focus on repetitive DNA elements.

Anostomidae are a neotropical fish family rich in number of species. Cytogenetically, they show a conserved karyotype with 2n = 54 chromosomes, although they present intraspecific/interspecific variations in the number and chromosomal location of repetitive DNA sequences. The aim of the present study was to perform a comparative description of the karyotypes of two populations of Leporinusfriderici Bloch, 1794 and three populations of Leporellusvittatus Valenciennes, 1850. We used conventional cytogenetic techniques allied to fluorescence in situ hybridization, using 18S ribosomal DNA (rDNA) and 5S rDNA, a general telomere sequence for vertebrates (TTAGGG)n and retrotransposon (RTE) Rex1 probes. The anostomids in all studied populations presented 2n = 54 chromosomes, with a chromosome formula of 32m + 22sm for L.friderici and 28m + 26sm for L.vittatus. Variations in the number and location of the 5S and 18S rDNA chromosomal sites were observed between L.friderici and L.vittatus populations and species. Accumulation of Rex1 was observed in the terminal region of most chromosomes in all populations, and telomere sequences were located just on all ends of the 54 chromosomes in all populations. The intraspecific and intergeneric chromosomal changes occurred in karyotype differentiation, indicating that minor chromosomal rearrangements had present in anostomid species diversification.