Cytogenetic Analysis, Heterochromatin Characterization and Location of the rDNA Genes of Hycleus scutellatus (Coleoptera, Meloidae); A Species with an Unexpected High Number of rDNA Clusters.

Laura Ruiz-Torres,Jesús Vela,Areli Ruiz-Mena,Eugenia E Montiel,Pedro Lorite,Francisco J Mancebo,Teresa Palomeque,Pablo Mora

doi:10.3390/insects12050385

Abstract

Simple SummaryThe family Meloidae contains approximately 3000 species, commonly known as blister beetles for their ability to secrete a substance called cantharidin, which causes irritation and blistering in contact with animal or human skin. In recent years there have been numerous studies focused on the anticancer action of cantharidin and its derivatives. Despite the recent interest in blister beetles, cytogenetic and molecular studies in this group are scarce and most of them use only classical chromosome staining techniques. The main aim of our study was to provide new information in Meloidae. In this study, cytogenetic and molecular analyses were applied for the first time in the family Meloidae. We applied fluorescence staining with DAPI and the position of ribosomal DNA in Hycleus scutellatus was mapped by FISH. Hycleus is one of the most species-rich genera of Meloidae but no cytogenetic data have yet been published for this particular genus. Additionally, we isolated a satellite DNA family located within the pericentromeric regions of all chromosomes. The results obtained in this study may be a suitable starting point to initiate more extensive cytogenetic analyses in this important species-rich genus, and in the family Meloidae in general.Meloidae are commonly known as blister beetles, so called for the secretion of cantharidin, a toxic substance that causes irritation and blistering. There has been a recent increase in the interest of the cantharidin anticancer potential of this insect group. Cytogenetic and molecular data in this group are scarce. In this study, we performed a karyotype analysis of Hycleus scutellatus, an endemic species of the Iberian Peninsula. We determined its chromosome number, 2n = 20, as well as the presence of the X and Y sex chromosomes. In addition to a karyotype analysis, we carried out DAPI staining. By fluorescence in situ hybridization we mapped the rDNA clusters on 12 different chromosomes. Compared to others, this species shows an unusually high number of chromosomes carrying rDNA. This is one of the highest numbers of rDNA sites found in the Polyphaga suborder (Coleoptera). Additionally, we isolated a satellite DNA family (Hyscu-H), which was located within the pericentromeric regions of all chromosomes, including the sex chromosomes. The results suggest that Hyscu-H is likely to be one of the most abundant satellite DNA repeats in H. scutellatus.

Highlights

The family Meloidae, commonly known as blister beetles or the Spanish fly, contains approximately 3000 species, divided among 125 genera and four subfamilies [1]
The recent interest in cantharidin and in its biosynthetic pathways has led to the genome sequencing of two of the most important blister beetles in traditional Chinese medicine; Hycleus cichorii and Hycleus phaleratus [8]
We identified a satellite DNA (satDNA) repeat that was located within the pericentromeric regions of all chromosomes, making it probably one of the most abundant satDNAs in this insect

Summary

Introduction

The family Meloidae, commonly known as blister beetles or the Spanish fly, contains approximately 3000 species, divided among 125 genera and four subfamilies [1]. The recent interest in cantharidin and in its biosynthetic pathways has led to the genome sequencing of two of the most important blister beetles in traditional Chinese medicine; Hycleus cichorii and Hycleus phaleratus [8]. A more recent study showed that the insect telomeric repeat, (TTAGG)n, was substituted for (TCAGG)n in all tested Tenebrionoidea species, among them a nonclassified blister beetle from the genus Mylabris [11]. The molecular cytogenetic analysis of the nucleolar organizer regions (NORs) has been widely used in the study of chromosomal evolution and phylogeny among related species [20,21]. The chromosomal localization of the rDNA clusters has been performed using silver staining techniques This technique shows two drawbacks: it only stains active NORs, that is, those that were transcribed during the previous interface [22], and in some cases stains heterochromatic regions [23,24].

Chromosome Preparations and DAPI Staining

Findings

Results and Discussion