Comparative FISH-mapping of TTAGG telomeric sequences to the chromosomes of leafcutter ants (Formicidae, Myrmicinae): is the insect canonical sequence conserved?

Abstract

Telomeric sequences are conserved across species. The most common sequence reported among insects is (TTAGG)n, but its universal occurrence is not a consensus because other canonical motifs have been reported. In the present study, we used fluorescence in situ hybridization (FISH) using telomeric probes with (TTAGG)6 repeats to describe the telomere composition of leafcutter ants. We performed the molecular cytogenetic characterization of six Acromyrmex Mayr, 1865 and one Atta Fabricius, 1804 species (Acromyrmex ambiguus (Emery, 1888), Ac. crassispinus (Forel, 1909), Ac. lundii (Guérin-Mèneville, 1838), Ac. nigrosetosus (Forel, 1908), Ac. rugosus (Smith, 1858), Ac. subterraneus subterraneus (Forel, 1893), and Atta sexdens (Linnaeus, 1758)) and described it using a karyomorphometric approach on their chromosomes. The diploid chromosome number 2n = 38 was found in all Acromyrmex species, and the karyotypic formulas were as follows: Ac. ambiguus 2K = 14M + 12SM + 8ST + 4A, Ac. crassispinus 2K = 12M + 20SM + 4ST + 2A, Ac. lundii 2K = 10M + 14SM + 10ST + 4A, Ac. nigrosetosus 2K = 12M + 14SM + 10ST + 2A, and Ac. subterraneus subterraneus 2K = 14M + 18SM + 4ST + 2A. The exact karyotypic formula was not established for Ac. rugosus. FISH analyses revealed the telomeric regions in all the chromosomes of the species studied in the present work were marked by the (TTAGG)6 sequence. These results reinforce the premise that Formicidae presents high homology between their genera for the presence of the canonical sequence (TTAGG)n.

Profiles of telomeric repeats in Insecta reveal diverse forms of telomeric motifs in Hymenopterans

“…Our extensive profiling of TRMs in major insect orders provided additional evidence to confirm that (TTAGG)n is the ancestral TRM in Insecta, as reported and summarized in the literature (Sahara et al, 1999;Sasaki & Fujiwara, 2000;Lorite et al, 2002;Frydrychova et al, 2004;Vitkova et al, 2005;Korandova et al, 2014;Menezes et al, 2017; Kuznetsova et al, 2019;de Castro et al, 2020). In addition to the insect orders, we discovered the (TTAGG)n TRM in Diplura, which is the immediate outgroup of Insecta (Fig 3).…”

Evolutionary insights into the genomic organization of major ribosomal DNA in ant chromosomes

“…In ants, the physical mapping of rDNA genes using the FISH technique was first described in Australian ants by Hirai et al (1994Hirai et al ( , 1996. Since then, the number of studies mapping these genes has increased (Mariano et al, 2008;Santos et al, 2016;Micolino et al, 2019a;Teixeira et al, 2020) and other repetitive sequences, such as telomeres (Meyne et al, 1995;Pereira et al, 2018;Micolino et al, 2020;Castro et al, 2020), satellite DNA (Lorite et al, 2004;Huang et al, 2016), 5S ribosomal genes (Aguiar et al, 2017), and microsatellites (Barros et al, 2018;Micolino et al, 2019b), have been mapped in the chromosomes using the FISH technique. To date, molecular cytogenetic studies on rDNA genes in ants have improved understanding of chromosomal evolution and phylogeny and provided taxonomic resolutions for different ant groups (Hirai et al, 1994(Hirai et al, , 1996Santos et al, 2010Santos et al, , 2016.…”

Organização cromossômica e dinâmica evolutiva de sequências repetitivas em formigas cultivadoras de fungos (Myrmicinae: Attini: Attina)

“…By contrast, the telomeric canonic motif TTAGG(n) of insects showed strong signals at the end of all the chromosomes of A. cephalotes, as in other ant species Lorite et al, 2002), including leaf-cutting ants Castro et al, 2020. Interstitial telomeric sequences can be considered relicts of the fusions of ancestral chromosomes (Lin and Yan, 2008;Olsson et al, 2018).…”

“…: Mariano et al 2008;Santos et al 2016;Aguiar et al 2017;Barros et al 2016Barros et al , 2021Barros et al , 2022Micolino et al 2019aMicolino et al , b, 2022Teixeira et al 2020). Outras sequências repetitivas também tem sido mapeadas com a FISH em diferentes espécies de formigas como a sequência telomérica canônica de insetos (TTAGG)n Micolino et al 2019aMicolino et al , b, 2020Castro et al 2020;Barros et al 2021), e mais recentemente, microssatélites em três espécies de formigas cultivadoras de fungos (Barros et al 2018;Micolino et al 2019a.…”

“…In contrast, the (GAG)10, (CAA)10, and (CGG)10 microsatellites did not show specific bands in M. holmgreni (Micolino et al, 2019). Additionally, other repetitive sequences, such as telomeric sequences, have been mapped on ant chromosomes, including leaf-cutting ants; they show that the TTAGG motif constitutes their telomeres Lorite et al, 2002;Castro et al, 2020;Teixeira et al, in prep. ).…”