Telomere structure in insects: A review

Abstract

Telomeres are terminal regions of chromosomes, which protect them from fusion with other chromosomes and stabilize their structure. Telomeres usually contain specific DNA repeats (motifs), which are maintained by telomerase, a kind of reverse transcriptase. In this review, we survey the current state of knowledge of telomere motifs in insects. Among Hexapoda, data on telomere composition are available for more than 350 species from 108 families and 25 orders. The telomere motif (TTAGG) n is considered ancestral for the class Insecta. However, certain insects have different and often unknown telomeric sequences. This apparently happens because telomerase-dependent mechanisms usually coexist with various means of alternative lengthening of telomeres as backup mechanisms of telomere maintenance. This coexistence can explain losses and reappearances of the TTAGG repeat and telomerase-dependent telomere replication in insect evolution. For example, a few higher taxa, such as Heteroptera (Hemiptera) and Hymenoptera, show presence of the (TTAGG) n motif in their basal clades as well as a subsequent loss and, at least in the Hymenoptera, independent reappearance of this repeat in some advanced groups. Analogously, most members of Coleoptera also retain the TTAGG repeat, although it is changed to TCAGG in certain families. Furthermore, the (TTAGG) n motif seems to have been irreversibly lost in the order Diptera. In this group, telomeric sequences are represented either by long terminal repeats or by retrotransposons. Retrotransposons are also interspersed with other telomeric sequences in many groups of insects. The accumulating data demonstrate that the class Insecta is substantially diverse in terms of its telomere structure. K E Y W O R D Schromosomes, FISH, insects, TTAGG, retrotransposons 128 |

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

“…In fact, the canonical motif (TTAGG) n was observed in several branches of the clade of fungus-farming ants, from anciently diverged lineages such as Mycetophylax to recent lineages such as Mycetomoellerius (Micolino et al 2019a(Micolino et al , b, 2020. Besides, the alternative TCAGG motif present in insects seems to be restricted to some groups, but not to Formicidae (Kuznetsova et al 2019), and we did not find any evidences for this in previously attempted experiments in our laboratory on the phylogenetic basis of fungus-farming ants (unpublished data). Sahara et al (1999) propose that (TTAGG) n is a sequence with high homology in Insecta because it is inherited from a common primitive ancestor of the class and the fact that some families do not show the presence of canonical repetition is explained by the group evolutionary process, where (TTAGG) n has been lost and recovered several times.…”

Rapid chromosomal evolution in the bush-cricket Gonatoxia helleri Hemp, 2016 (Orthoptera, Phaneropterinae)

“…Another universal probe is the telomeric sequence [tDNA, (TTAGG) n ]) that itself is an ideal marker for the identification of chromosome ends (Kuznetsova et al 2020) and a marker for chromosome rearrangements, being conserved in many groups of insects (Vítková et al 2005). Interstitial telomeric sequences (ITSs) reflect remnants of multiple chromosome fusions of ancestral chromosomes e.g.…”

Karyotypes diversity in some Iranian Pamphagidae grasshoppers (Orthoptera, Acridoidea, Pamphagidae): new insights on the evolution of the neo-XY sex chromosomes

“…The fluorescence in situ hybridization (FISH) with telomeric probe and rDNA genes is a very useful tool for comparative analysis of karyotype in Orthoptera insects (Warchałowska-Śliwa et al 2020). In addition, the determination of the position of telomeric and rDNA repeats in chromosomes of many groups of insects made it possible to identify the mechanisms of structural rearrangements (Kuznetsova et al 2019). It is known that telomeres play an important role in the stability of the eukaryotic karyotype.…”