Comparative cytogenetics of Lachnaia species (Coleoptera: Chrysomelidae) reveals a novel telomeric motif (TTTGG) in insects

Abstract

Cytogenetic analyses of Lachnaia hirta, Lachnaia tristigma, and Lachnaia vicina have revealed that all species show a similar karyotype with 2n=24 and a meioformula of 11+Xy+. Despite this, their sex chromosomes show certain diferences in morphology. All species exhibit pericentromeric heterochromatin on all autosomes and X chromosomes, with the Y chromosome being heterochromatic. The X and Y chromosomes carry the nucleolar organizer regions in the three species, althoug L. vicina also has them in one autosomal pair. No clear hybridization signals were obtained using a probe with the TTAGG repeat, which is the ancestral DNA motif of telomeres in insects. The genomes of the three species have been sequenced. The obtained data have been used for the identifcation of telomeric motifs through bioinformatics analyses, including the Telomeric Repeats Identifcation Pipeline, a bioinformatics tool for identifying telomeric repeat motifs. According to the data, the TTTGG sequence is suggested as the telomeric repeat in these species, a fnding confrmed by fuorescence in situ hybridization. The TTTGG motif constitutes a new telomeric repeat motif in Coleoptera. This new motif has been found at the chromosome ends of another beetle species, the oak borer Platypus cylindrus (Coleoptera, Curculionidae), and in a wasp species, Oxytorus armatus (Hymenoptera, Ichneumonoidea), whose genomes are assembled at the chromosome level. The detection of this telomeric repeat in two families of beetles and in a hymenopteran species suggests that this new telomeric motif has independently emerged in evolutionarily distant groups of insects.