The Chromosomes of Lepturinae (Coleoptera: Cerambycidae) II. A study of 8 more species, with focus on Desmocerus palliatus

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Karyotype diversity suggests that Laonastes aenigmamus (Laotian rock rat) (Rodentia, Diatomyidae) is a multi-specific genus

International audienceLaonastes aenigmamus (Khanyou) is a recently described rodent species living in geographically separated limestone formations of the Khammuan Province in Lao PDR. Chromosomes of 21 specimens of L. aenigmamus were studied using chromosome banding as well as fluorescent in situ hybridization (FISH) techniques using human painting, telomere repeats , and 28S rDNA probes. Four different karyotypes were established. Study with human chromosome paints and FISH revealed that four large chromosomes were formed by multiple common tandem fusions, with persistence of some interstitial telomeres. The rearrangements separating the different karyotypes (I to IV) were also reconstructed. Various combinations of Robertsonian translocations or tandem fusions involving the same chromosomes differentiate these karyo-types. These rearrangements create a strong gametic barrier, which isolates specimens with karyotype II from the others. C-banding and FISH with telomere repeats also exhibit large and systematized differences between karyotype II and others. These data indicate an ancient reproductive separation and suggest that Laonastes is not a mono-specific genus

Chromosomal and genetic characterization of four Caribbean Prioninae (Coleoptera: Cerambycidae) species with notes on biogeography

Chromosomes of four rare and localized Caribbean Prioninae (Coleoptera: Cerambycidae) species were analysed. All have 26, XY karyotypes. Those of Solenoptera canaliculata (Solenopterini) from Guadeloupe nearby islands Les Saintes and Marie-Galante and S. quadrilineata from Martinique look similar. They have a single pair of sub-metacentric autosomes. The karyotype of S. touroulti from St. Lucia has three sub-metacentric pairs. It appears closer to that of Hovorodon maxillosum (Mallodontini) from Marie-Galante which has ten sub-metacentric pairs. The CO1 gene sequence, taking two European species Aegosoma scabricorne (Prioninae: Aegosomatini) and Ergates faber (Prioninae: Ergatini) as external groups was analysed in S. canaliculata and S. quadrilineata. In spite of their karyotype similarity, their CO1 genes differ by a strong accumulation of mutations. Thus, either chromosomal or genetic data confirm the species status of the three closely related Solenoptera species. Ten different CO1 haplotypes are found among the 21 specimens of S. canaliculata studied from les Saintes and Marie-Galante. Both different haplotypes were found in each island and identical haplotypes were found in different islands. Hence, the gene flow was not interrupted. Biogeographical parameters favor the hypothesis that repeated passages between islands were made possible by floating trunks, principally from Les Saintes to Marie-Galante

Preferential binding of a G-quadruplex ligand to human chromosome ends

The G-overhangs of telomeres are thought to adopt particular conformations, such as T-loops or G-quadruplexes. It has been suggested that G-quadruplex structures could be stabilized by specific ligands in a new approach to cancer treatment consisting in inhibition of telomerase, an enzyme involved in telomere maintenance and cell immortality. Although the formation of G-quadruplexes was demonstrated in vitro many years ago, it has not been definitively demonstrated in living human cells. We therefore investigated the chromosomal binding of a tritiated G-quadruplex ligand, (3)H-360A (2,6-N,N′-methyl-quinolinio-3-yl)-pyridine dicarboxamide [methyl-(3)H]. We verified the in vitro selectivity of (3)H-360A for G-quadruplex structures by equilibrium dialysis. We then showed by binding experiments with human genomic DNA that (3)H-360A has a very potent selectivity toward G-quadruplex structures of the telomeric 3′-overhang. Finally, we performed autoradiography of metaphase spreads from cells cultured with (3)H-360A. We found that (3)H-360A was preferentially bound to chromosome terminal regions of both human normal (peripheral blood lymphocytes) and tumor cells (T98G and CEM1301). In conclusion, our results provide evidence that a specific G-quadruplex ligand interacts with the terminal ends of human chromosomes. They support the hypothesis that G-quadruplex ligands induce and/or stabilize G-quadruplex structures at telomeres of human cells

The heterochromatic chromosome caps in great apes impact telomere metabolism.

In contrast with the limited sequence divergence accumulated after separation of higher primate lineages, marked cytogenetic variation has been associated with the genome evolution in these species. Studying the impact of such structural variations on defined molecular processes can provide valuable insights on how genome structural organization contributes to organismal evolution. Here, we show that telomeres on chromosome arms carrying subtelomeric heterochromatic caps in the chimpanzee, which are completely absent in humans, replicate later than telomeres on chromosome arms without caps. In gorilla, on the other hand, a proportion of the subtelomeric heterochromatic caps present in most chromosome arms are associated with large blocks of telomere-like sequences that follow a replication program different from that of bona fide telomeres. Strikingly, telomere-containing RNA accumulates extrachromosomally in gorilla mitotic cells, suggesting that at least some aspects of telomere-containing RNA biogenesis have diverged in gorilla, perhaps in concert with the evolution of heterochromatic caps in this species

Chromosomal Instability in Near-Diploid Colorectal Cancer: A Link between Numbers and Structure

Chromosomal instability (CIN) plays a crucial role in tumor development and occurs mainly as the consequence of either missegregation of normal chromosomes (MSG) or structural rearrangement (SR). However, little is known about the respective chromosomal targets of MSG and SR and the way these processes combined within tumors to generate CIN. To address these questions, we karyotyped a consecutive series of 96 near-diploid colorectal cancers (CRCs) and distinguished chromosomal changes generated by either MSG or SR in tumor cells. Eighty-three tumors (86%) presented with chromosomal abnormalities that contained both MSGs and SRs to varying degrees whereas all 13 others (14%) showed normal karyotype. Using a maximum likelihood statistical method, chromosomes affected by MSG or SR and likely to represent changes that are selected for during tumor progression were found to be different and mostly mutually exclusive. MSGs and SRs were not randomly associated within tumors, delineating two major pathways of chromosome alterations that consisted of either chromosome gains by MSG or chromosomal losses by both MSG and SR. CRCs showing microsatellite instability (MSI) presented with either normal karyotype or chromosome gains whereas MSS (microsatellite stable) CRCs exhibited a combination of the two pathways. Taken together, these data provide new insights into the respective involvement of MSG and SR in near-diploid colorectal cancers, showing how these processes target distinct portions of the genome and result in specific patterns of chromosomal changes according to MSI status

Different behaviour of C-banded peri-centromeric heterochromatin between sex chromosomes and autosomes in Polyphagan beetles

International audienceCitation: Dutrillaux AM , Dutrillaux B (2019) Different behaviour of C-banded peri-centromeric heterochromatin between sex chromosomes and autosomes in Polyphagan beetles. Comparative Cytogenetics @@(@@): @-@. https://doi. Abstract Heterochromatin variation was studied after C-banding of male karyotypes with a XY sex formula from 224 species belonging to most of the main families of Coleoptera. The karyotypes were classified in relation with the ratio heterochromatin/euchromatin total amounts and the amounts of heterochromatin on autosomes and gonosomes were compared. The C-banded karyotypes of 19 species, representing characteristic profiles are presented. This analysis shows that there is a strong tendency for the homogenization of the size of the peri-centromeric C-banded heterochromatin on autosomes. The amount of heterochromatin on the X roughly follows the variations of autosomes. At contrast, the C-banded heterochromatin of the Y, most frequently absent or very small and rarely amplified, looks quite independent from that of other chromosomes. We conclude that the Xs and autosomes, but not the Y, possibly share some, but not all mechanisms of heterochromatin amplifi-cation/reduction. The theoretical models of heterochromatin expansion are discussed in the light of these data

A propos des variations de coloration, liées au sexe (hétérochromatisme sexuel) ou non (Polychromatisme), chez les Cerambycidae de la faune de France (Coleoptera)

About colour variation related to sex (sexual heterochromatism) or not (polychromatism) in Cerambycidae from French fauna (Coleoptera). Colour patterns of Cerambycidae (Coleoptera) from French fauna are analysed in relation to the sex. It is shown, using a few examples, that extreme colour patterns, often described as varieties, are unevenly distributed among males and females. It is proposed to call sex heterochromatism and polychromatism sex-linked and non sex-linked variations, respectively. Polychromatism is frequent in all sub-families, whereas sex heterochromatism is frequent in Lepturinae only, in which it involves elytrons principally. Sex heterochromatism rarely involves colour by reflexion or pubescence, and thus, is rarely observed in Lamiinae species which are generally covered by pubescence. For explaining the occurrence of sex heterochromatism in the absence of sex hormones, it is proposed that it relies on chronological differences between morphogenesis (early) and chromogenesis (late) rather invariable, and gonad development, highly variable among taxa and differing with the sex. These steps of metamorphosis are under the control of the same juvenile and ecdysteroid hormones, but at a given time, gonads become ecdysteroid producer. These hormones could inhibit a concomitant step of melanogenesis and activate other pigmentation pathways. Elytrons, whose chromogenesis is very late, frequently display sex heterochromatism, which may contribute to a better identification of sex partners.Une analyse de la coloration des Cerambycidae de la faune de France est réalisée en recherchant, aussi systématiquement que possible, des différences entre mâles et femelles. A l'aide de quelques exemples, il est montré que les formes extrêmes de coloration, souvent décrites comme des variétés, se distribuent inégalement dans les deux sexes. Il est proposé d'appeler hétérochromatisme sexuel et polychromatisme les variations respectivement liées et non liées au sexe. Alors que le polychromatisme est fréquent dans toutes les sous-familles, l'hétérochromatisme sexuel ne se rencontre fréquemment que chez les Lepturinae, où il touche principalement la mélanogenèse élytrale. Les colorations par réflexion ou pubescence sont peu sujettes à l'hétérochromatisme sexuel, qui de ce fait est quasi-inexistant chez les Lamiinae, qui sont couverts de pubescence. Pour expliquer la survenue de l'hétérochromatisme sexuel en l'absence d'hormones sexuelles mâle et femelle, il est proposé qu'il repose, comme peut-être le dimorphisme sexuel, sur les différences de chronologies entre, d'une part, la morphogenèse (précoce) et la chromogenèse (tardive) peu variables et, d'autre part, le développement des gonades, très variable d'un taxon à l'autre et différent selon le sexe. Ces étapes de la métamorphose sont sous le contrôle des mêmes hormones ecdystéroides et juvéniles, mais à un moment donné, les gonades deviennent productrices d'ecdystéroides. Ces hormones peuvent alors inhiber une étape concomitante de la mélanogenèse, et éventuellement activer un autre mode de pigmentation. Les élytres, dont la chromogenèse est la plus tardive, sont particulièrement concernés par l'hétérochromatisme sexuel, ce qui peut permettre une meilleure identification des partenaires sexuels.Dutrillaux Bernard. A propos des variations de coloration, liées au sexe (hétérochromatisme sexuel) ou non (Polychromatisme), chez les Cerambycidae de la faune de France (Coleoptera). In: Bulletin de la Société entomologique de France, volume 113 (2), juin 2008. pp. 155-172

Telomeric heterochromatin and meiotic recombination in three species of Coleoptera (Dorcadion olympicum Ganglebauer, Stephanorrhina princeps Oberthür and Macraspis tristis Laporte)

International audienceCentromeres are generally embedded in heterochromatin, which is assumed to have a negative impact on meiotic recombination in adjacent regions, a condition required for the correct segregation of chromosomes at anaphase I. At difference, telomeric and interstitial regions rarely harbour large heterochromatic fragments. We observed the presence at the heterozygote status of heterochromatin in telomere region of some chromosomes in 3 species of Coleoptera: Dorcadion olympicum; Stephanorrhina princeps and Macraspis tristis. This provided us with the opportunity to study the relationship between heterochromatin, chiasma location and meiotic recombination independently from the proximity of centromeres in this order of insects. In acrocentric chromosomes, the presence of heterochromatin in telomere region of the long arm displaces recombination near the centromere. In sub-metacentrics, recombination is almost always restricted to the other arm. This at distance effect of heterochromatin may deeply influence genetic drift