Comparative Cytogenetic and Sequence Analysis of U Small Nuclear RNA Genes in Three Ancistrus Species (Siluriformes: Loricariidae).

Ancistrus presents a wide karyotypic diversity, resulting from numeric and structural chromosomal rearrangements. It has been proposed that some genome-specific regions containing repetitive units could organize prone-to-break DNA sites in Loricariidae, triggering chromosomal rearrangements such as Robertsonian fusions (Rb fusions), centric fissions, translocations, and inversions. The tandemly repeats of the small nuclear RNAs (snRNAs) gene families are considered good cytogenetic markers for understanding chromosomal remodeling events among closely related species, but these snRNAs have been scarcely analyzed in Ancistrus. This study presented the nucleotide sequencing and comparative in situ location of U snRNA sequences from Ancistrus aguaboensis, Ancistrus cf. multispinis, and Ancistrus sp. (2n = 50, 52, and 50, respectively), aiming to provide information about snRNA clusters in the genome and chromosome evolution in Ancistrus. U snRNA nucleotide sequences of Ancistrus presented identity to orthologous copies and folded their secondary structures correctly. In situ localization and karyotyping of the three Ancistrus species revealed clustered copies of U2 and U5 snRNA gene families to a single chromosome site, one chromosome pair bearing U1 snRNA sequence, and one main locus of U4 snRNA sequence, besides scattered signals along the chromosomes. Previous studies related the participation of the rRNA gene families in centric fusion events, contributing to chromosome rearrangements and karyotype plasticity present in Loricariidae. In this study, homeologies in U snRNA loci chromosomal locations were detected, indicating the occurrence of conserved sites of these gene families in these three Ancistrus species with 2n = 50 or 52 chromosomes.