U1 snDNA clusters in grasshoppers: chromosomal dynamics and genomic organization

Abstract

The spliceosome, constituted by a protein set associated with small nuclear RNA (snRNA), is responsible for mRNA maturation through intron removal. Among snRNA genes, U1 is generally a conserved repetitive sequence. To unveil the chromosomal/genomic dynamics of this multigene family in grasshoppers, we mapped U1 genes by fluorescence in situ hybridization in 70 species belonging to the families Proscopiidae, Pyrgomorphidae, Ommexechidae, Romaleidae and Acrididae. Evident clusters were observed in all species, indicating that, at least, some U1 repeats are tandemly arrayed. High conservation was observed in the first four families, with most species carrying a single U1 cluster, frequently located in the third or fourth longest autosome. By contrast, extensive variation was observed among Acrididae, from a single chromosome pair carrying U1 to all chromosome pairs carrying it, with occasional occurrence of two or more clusters in the same chromosome. DNA sequence analysis in Eyprepocnemis plorans (species carrying U1 clusters on seven different chromosome pairs) and Locusta migratoria (carrying U1 in a single chromosome pair) supported the coexistence of functional and pseudogenic lineages. One of these pseudogenic lineages was truncated in the same nucleotide position in both species, suggesting that it was present in a common ancestor to both species. At least in E. plorans, this U1 snDNA pseudogenic lineage was associated with 5S rDNA and short interspersed elements (SINE)-like mobile elements. Given that we conclude in grasshoppers that the U1 snDNA had evolved under the birth-and-death model and that its intragenomic spread might be related with mobile elements.

Chromosomal evolutionary dynamics of four multigene families in Coreidae and Pentatomidae (Heteroptera) true bugs

“…Among these, some multigene families are tandemly organized, and the chromosomal location of these sequences has been useful for the elucidation of chromosomal evolution in different groups, including insects (see for example Cabrero et al 2009;Nguyen et al 2010;Cabral-de-Mello et al 2011a, b;Bardella et al 2013;Anjos et al 2015). The multigene families most used as chromosomal markers in insects; i.e., rDNAs, histone genes and, to a lesser extent, U snDNA, have revealed variable patterns for the number and location of the clusters, depending on the group studied.…”

Karyotypes and Repetitive DNA Evolution in Six Species of the Genus <b><i>Mahanarva </i></b>(Auchenorrhyncha: Cercopidae)

“…These repetitive sequences represent excellent chromosomal markers and have been successfully used for the understanding of chromosomal evolution in distinct insect orders [e.g., Palomeque and Lorite, 2008;Nguyen et al, 2010;Anjos et al, 2015]. In species with holocentric chromosomes, repetitive DNA markers are even more important to understand evolution, due to the lack of other chromosomal features, such as the primary constriction, allowing the identification of specific chromosomes or chromosomal regions [Pita et al, 2014;Kuznetsova and Aguin-Pombo, 2015].…”

Insights into chromosomal evolution of Cicadomorpha using fluorochrome staining and mapping 18S rRNA and H3 histone genes

“…This species represents an exceptional case of high 18S loci in Hemiptera. Dispersed 18S loci could result from genomic amplification followed by spread, as previously suggested for repetitive sequences in insect chromosomes (Anjos et al., ; Cabral‐de‐Mello, Cabrero, López‐León, & Camacho, ; Cabral‐de‐Mello, Moura, Melo, & Martins, ; Cabrero & Camacho, ). The occurrence of 18S on sex chromosomes in Mahanarva tristis and Amblyophallus exaltatus suggests putative transposition and large chromosome rearrangements, respectively, which are involved in the relocation of 18S clusters.…”