Paracentric Inversions Differentiate the Conservative Karyotypes in Two Centropomus Species (Teleostei: Centropomidae)

Centropomus is the sole genus of the Centropomidae family (Teleostei), comprising 12 species widely distributed throughout the Western Atlantic and Eastern Pacific, with 6 of them occurring in the Western Atlantic in extensive sympatry. Their life history and phylogenetic relationships are well characterized; however, aspects of chromosomal evolution are still unknown. Here, cytogenetic analyses of 2 Centropomus species of great economic value (C. undecimalis and C. mexicanus) were performed using conventional (Giemsa, Ag-NOR, and fluorochrome staining, C- and replication banding) and molecular (chromosomal mapping of 18S and 5S rDNA, H2A-H2B and H3 hisDNA, and (TTAGGG)n repeats) approaches. The karyotypes of both species were composed of 48 solely acrocentric chromosomes (2n = 48; FN = 48), but the single ribosomal site was located in varying positions in the long arms of the second largest chromosome pair. Replication bands were generally similar, although conspicuous differences were observed in some chromosome regions. In both species, the histone H3 genes were located on 3 apparently homeologous chromosome pairs, but the exact position of these clusters differed slightly. Interspecific hisDNA and rDNA site displacements can indicate the occurrence of multiple paracentric inversions during the evolutionary diversification of the Centropomus genomes. Although the karyotypes remained similar in both species, our data demonstrate an unsuspected microstructural reorganization between them, driven most likely by a series of paracentric inversions.

Comparative analysis based on replication banding reveals the mechanism responsible for the difference in the karyotype constitution of treefrogs Ololygon and Scinax (Arboranae, Hylidae, Scinaxinae)

According to the recent taxonomic and phylogenetic revision of the family Hylidae, species of the former Scinaxcatharinae (Boulenger, 1888) clade were included in the resurrected genus Ololygon Fitzinger, 1843, while species of the Scinaxruber (Laurenti, 1768) clade were mostly included in the genus Scinax Wagler, 1830, and two were allocated to the newly created genus JulianusDuellman et al., 2016. Although all the species of the former Scinax genus shared a diploid number of 2n = 24 and the same fundamental number of chromosome arms of FN = 48, two karyotypic constitutions were unequivocally recognized, related mainly to the distinct size and morphology of the first two chromosome pairs. Some possible mechanisms for these differences had been suggested, but without any experimental evidence. In this paper, a comparison was carried out based on replication chromosome banding, obtained after DNA incorporation of 5-bromodeoxiuridine in chromosomes of Ololygon and Scinax. The obtained results revealed that the loss of repetitive segments in chromosome pairs 1 and 2 was the mechanism responsible for karyotype difference. The distinct localization of the nucleolus organizer regions in the species of both genera also differentiates the two karyotypic constitutions.

Comparative analysis based on replication banding reveals the mechanism responsible for the difference in the karyotype constitution of treefrogs Ololygon and Scinax (Arboranae, Hylidae, Scinaxinae)

According to the recent taxonomic and phylogenetic revision of the family Hylidae, species of the former Scinaxcatharinae (Boulenger, 1888) clade were included in the resurrected genus Ololygon Fitzinger, 1843, while species of the Scinaxruber (Laurenti, 1768) clade were mostly included in the genus Scinax Wagler, 1830, and two were allocated to the newly created genus JulianusDuellman et al., 2016. Although all the species of the former Scinax genus shared a diploid number of 2n = 24 and the same fundamental number of chromosome arms of FN = 48, two karyotypic constitutions were unequivocally recognized, related mainly to the distinct size and morphology of the first two chromosome pairs. Some possible mechanisms for these differences had been suggested, but without any experimental evidence. In this paper, a comparison was carried out based on replication chromosome banding, obtained after DNA incorporation of 5-bromodeoxiuridine in chromosomes of Ololygon and Scinax. The obtained results revealed that the loss of repetitive segments in chromosome pairs 1 and 2 was the mechanism responsible for karyotype difference. The distinct localization of the nucleolus organizer regions in the species of both genera also differentiates the two karyotypic constitutions.

Chromosome Banding in Amphibia. XXXII. The Genus Xenopus (Anura, Pipidae)

Mitotic chromosomes of 16 species of the frog genus Xenopus were prepared from kidney and lung cell cultures. In the chromosomes of 7 species, high-resolution replication banding patterns could be induced by treating the cultures with 5-bromodeoxyuridine (BrdU) and deoxythymidine (dT) in succession, and in 6 of these species the BrdU/dT-banded chromosomes could be arranged into karyotypes. In the 3 species of the clade with 2n = 20 and 4n = 40 chromosomes (X. tropicalis, X. epitropicalis, X. new tetraploid 1), as well as in the 3 species with 4n = 36 chromosomes (X. laevis, X. borealis, X. muelleri), the BrdU/dT-banded karyotypes show a high degree of homoeology, though differences were detected between these groups. Translocations, inversions, insertions or sex-specific replication bands were not observed. Minor replication asynchronies found between chromosomes probably involve heterochromatic regions. BrdU/dT replication banding of Xenopus chromosomes provides the landmarks necessary for the exact physical mapping of genes and repetitive sequences. FISH with an X. laevis 5S rDNA probe detected multiple hybridization sites at or near the long-arm telomeric regions in most chromosomes of X. laevis and X. borealis, whereas in X. muelleri, the 5S rDNA sequences are located exclusively at the long-arm telomeres of a single chromosome pair. Staining with the AT base pair-specific fluorochrome quinacrine mustard revealed brightly fluorescing heterochromatic regions in the majority of X. borealis chromosomes which are absent in other Xenopus species.

Autism Spectrum Disorder in a Girl with aDe NovoX;19 Balanced Translocation

Balanced X-autosome translocations are rare, and female carriers are a clinically heterogeneous group of patients, with phenotypically normal women, history of recurrent miscarriage, gonadal dysfunction, X-linked disorders or congenital abnormalities, and/or developmental delay. We investigated a patient with ade novoX;19 translocation. The six-year-old girl has been evaluated due to hyperactivity, social interaction impairment, stereotypic and repetitive use of language with echolalia, failure to follow parents/caretakers orders, inconsolable outbursts, and persistent preoccupation with parts of objects. The girl has normal cognitive function. Her measurements are within normal range, and no other abnormalities were found during physical, neurological, or dysmorphological examinations. Conventional cytogenetic analysis showed ade novobalanced translocation, with the karyotype 46,X,t(X;19)(p21.2;q13.4). Replication banding showed a clear preference for inactivation of the normal X chromosome. The translocation was confirmed by FISH and Spectral Karyotyping (SKY). Although abnormal phenotypes associated withde novobalanced chromosomal rearrangements may be the result of disruption of a gene at one of the breakpoints, submicroscopic deletion or duplication, or a position effect, X; autosomal translocations are associated with additional unique risk factors including X-linked disorders, functional autosomal monosomy, or functional X chromosome disomy resulting from the complex X-inactivation process.

Chromosome Mapping of Repetitive Sequences inRachycentron canadum(Perciformes: Rachycentridae): Implications for Karyotypic Evolution and Perspectives for Biotechnological Uses

The cobia,Rachycentron canadum, a species of marine fish, has been increasingly used in aquaculture worldwide. It is the only member of the family Rachycentridae (Perciformes) showing wide geographic distribution and phylogenetic patterns still not fully understood. In this study, the species was cytogenetically analyzed by different methodologies, including Ag-NOR and chromomycin A3(CMA3)/DAPI staining, C-banding, early replication banding (RGB), andin situfluorescent hybridization with probes for 18S and 5S ribosomal genes and for telomeric sequences (TTAGGG)n. The results obtained allow a detailed chromosomal characterization of the Atlantic population. The chromosome diversification found in the karyotype of the cobia is apparently related to pericentric inversions, the main mechanism associated to the karyotypic evolution of Perciformes. The differential heterochromatin replication patterns found were in part associated to functional genes. Despite maintaining conservative chromosomal characteristics in relation to the basal pattern established for Perciformes, some chromosome pairs in the analyzed population exhibit markers that may be important for cytotaxonomic, population, and biodiversity studies as well as for monitoring the species in question.