Localization and activity of rDNA genes in tiger beetles (Coleoptera: Cicindelidae).
ABSTRACT Siver staining of male meiotic nuclei of six species f the tiger beetle genus Cicindela (tribe Cicindelini), with multiple sex chromosomes, reveals the presence of active nucleolar organizing regions (NORs) in the sex vesicle. In one species, Cicindela melancholica, fluorescence in situ hybridization b(FISH) with a ribosomal probbe showed that rDNA genes are in one of the three X chromosomes and in the Y chromosome. Silver staining and FISH show that the related species Cicindela paludosa with a male XO system. has NORs located in one pair of autosomes. In Megacephala euphratica (tribe Megacephalini) these techniques indicate that NORs are located in three autosomal pairs but not in the single X chromosomes of males. In all these species the nucleolus can be seen from the onset of meiosis to the end of the diffuse stage; it disappears from diplotene to the end of meiosis and appears again during the spermatid stage. From these results it is concluded that: (i) the nucleolus does not seem to play a major role in the pairing and association of the multiple sex chromosomes during first meiotic prophase and metaphase; (ii) the occurrence of NORs in the heterosomes of species having multiple sex chromosomes is thought to be an ancestral condition for the genus Cicindela; and (iii) changes of location of NORs from heterosomes to the autosomes have occurred within species of this genus, at least in species showing extensive karyotypic repatterning.
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ABSTRACT: The Xy(p) sex determination mechanism is the system most frequent and ancestral to Coleoptera. Moreover, the presence of argyrophilous material associated with the sex bivalent is described as being responsible for the maintenance and association of these chromosomes. There are no karyotype data available regarding the genus Lagria and no consensus in the literature regarding the argyrophilous material present in the lumen of sex bivalent. Therefore, the aim of this work was to investigate the mechanism of sex chromosome bivalent association in Lagria villosa by analyzing the argyrophilous nature of the material present in the Xy(p) lumen. It was also intended to characterize L. villosa cytogenetically. The analysis of meiotic cells showed 2n = 18 = 16+Xy(p) for males and 2n = 18 = 16+XX in females and the meiotic formula was 2n = 8(II)+Xy(p). The C-banding showed blocks of pericentromeric heterochromatin in all chromosomes except in the y(p) chromosome. In these regions, the use of fluorochromes revealed the presence of heterochromatin containing GC rich DNA sequences. The study of synaptonemal complex showed a gradual increase in the electron-density of the axial elements of the sex chromosomes and their association with strongly electron-dense material. The pepsin pretreatment revealed that the material impregnated by silver is protein.Cytogenetic and Genome Research 08/2012; · 1.84 Impact Factor