R.F. Artoni

Physical Mapping of 5S rDNA in Two Species of Knifefishes: Gymnotus pantanal and Gymnotus paraguensis (Gymnotiformes)

Physical mapping of 5S rDNA in 2 species of knifefishes, Gymnotuspantanal and G. paraguensis (Gymnotiformes), was performed using fluorescence in situ hybridization with a 5S rDNA probe. The 5S rDNA PCR product from the genomes of both species was also sequenced and aligned to determine non-transcribed spacer sequences (NTS). Both species under study had different patterns of 5S rDNA gene cluster distribution. While in the karyotype of G. pantanal two 5S rDNA-bearing pairs were observed, the karyotype of G. paraguensis possessed as many as 19 such pairs. Such multiplication of 5S rDNA gene clusters might be caused by the involvement of transposable elements because the NTS of G. paraguensis was 400 bp long with high identity (90%) with a mobile transposable element called Tc1-like transposon, described from the cyprinid fish Labeo rohita.

Karyotype variability in neotropical catfishes of the family Pimelodidae (Teleostei: Siluriformes)

Karyotypic data are presented for four species of fish belonging to the Pimelodidae family. These species show a conserved diploid number, 2n = 56 chromosomes, with different karyotypic formulae. The analyzed species showed little amount of heterochromatin located preferentially in the centromeric and telomeric regions of some chromosomes. The nucleolus organizer regions activity (Ag-NORs) and the chromosomal location of ribosomal genes by fluorescent in situ hybridization (FISH), with 18S and 5S probes, showing only one chromosome pair marked bearer of ribosomal genes, the only exception was Pimelodus britskii that presented multiple NORs and syntenic location of the 18S and 5S probes. Non-Robertsonian events, as pericentric inversion and NORs duplication are requested to explain the karyotype diversification in Pseudoplatystoma from the rio Paraguay (MS), Pimelodus from the rio Iguacu (PR), Sorubim from the rio Paraguay (MS) and Steindachneridion from the rio Paraiba do Sul (SP). The obtained data for the karyotype macrostructure of these species corroborates a conserved pattern observed in Pimelodidae. On the other hand, interspecific variations detected by molecular cytogenetics markers made possible cytotaxonomic inferences and differentiation of the species here analyzed. Dados cariotipicos sao apresentados para quatro especies da familia Pimelodidae. Todas apresentaram o mesmo numero diploide, 2n = 56 cromossomos, com diferencas nas formulas cariotipicas. As especies aqui analisadas mostraram pouca quantidade de heterocromatina localizada preferencialmente na regiao centromerica e telomerica de alguns cromossosmos do complemento cariotipico. As regioes organizadoras de nucleolo (Ag-RONs) e a localizacao dos genes ribossomais pela hibridizacao in situ fluorescente (FISH), com sondas 18S e 5S, evidenciaram somente um par cromossomico marcado portador de genes ribossomais, a excecao de Pimelodus britskii que apresentou NORs multiplas e localizacao sintenica das sondas 18S e 5S. Eventos nao-Robertsonianos, como inversao pericentrica e duplicacao das NORs sao requeridos para explicar a diversificacao cariotipica em Pseudoplatystoma do rio Paraguai (MS), Pimelodus do rio Iguacu (PR), Sorubim do rio Paraguai (MS) e Steindachneridion do rio Paraiba do Sul (SP). Os dados obtidos para a macroestrutura cariotipica destas especies corrobora um padrao conservado observado na familia Pimelodidae. Por outro lado, evidencias de variacoes interespecificas pelos marcadores de citogenetica molecular empregados possibilitam inferencias citotaxonomicas e diferenciacao das especies aqui analisadas.

Swim training restores glucagon-like peptide-1 insulinotropic action in pancreatic islets from monosodium glutamate-obese rats

Glucagon‐like peptide‐1 (GLP‐1) is an important modulator of insulin secretion by endocrine pancreas. In the present study, we investigated the effect of swim training on GLP‐1 insulinotropic action in pancreatic islets from monosodium glutamate (MSG)‐obese rats.

Erratum to: Identification and chromosome mapping of repetitive elements in the Astyanax scabripinnis (Teleostei: Characidae) species complex

Most part of the eukaryotic genome is composed of repeated sequences or multiple copies of DNA, which were considered as “junk DNA”, and may be associated to the heterochromatin. In this study, three populations of Astyanax aff. scabripinnis from Brazilian rivers of Guaratingueta and Pindamonhangaba (Sao Paulo) and a population from Maringa (Parana) were analyzed concerning the localization of the nucleolar organizer regions (Ag-NORs), the As51 satellite DNA, the 18S ribosomal DNA (rDNA), and the 5S rDNA. Repeated sequences were also isolated and identified by the Cot − 1 method, which indicated similarity (90 %) with the LINE UnaL2 retrotransposon. The fluorescence in situ hybridization (FISH) showed the retrotransposon dispersed and more concentrated markers in centromeric and telomeric chromosomal regions. These sequences were co-localized and interspaced with 18S and 5S rDNA and As51, confirmed by fiber-FISH essay. The B chromosome found in these populations pointed to a conspicuous hybridization with LINE probe, which is also co-located in As51 sequences. The NORs were active at unique sites of a homologous pair in the three populations. There were no evidences that transposable elements and repetitive DNA had influence in the transcriptional regulation of ribosomal genes in our analyses.

Repetitive DNA and Meiotic Behavior of Sex Chromosomes in Gymnotus pantanal (Gymnotiformes, Gymnotidae)

Neotropical fishes have a low rate of chromosome differentiation between sexes. The present study characterizes the first meiotic analysis of sex chromosomes in the order Gymnotiformes. Gymnotus pantanal – females had 40 chromosomes (14m/sm, 26st/a) and males had 39 chromosomes (15m/sm, 24st/a), with a fundamental number of 54 – showed a multiple sexual determination chromosome system of the type X₁X₁X₂X₂/X₁X₂Y. The heterochromatin is restricted to centromeres of all chromosomes of the karyotype. The meiotic behavior of sex chromosomes involved in this system in males is from a trivalent totally pared in the pachytene stage, with a high degree of similarity. The cells of metaphase II exhibit 19 and 20 chromosomes, normal disjunction of sex chromosomes and the formation of balanced gametes with 18 + Y and 18 + X₁X₂ chromosomes, respectively. The small amount of heterochromatin and repetitive DNA involved in this system and the high degree of chromosome similarity indicated a recent origin of the X₁X₁X₂X₂/X₁X₂Y system in G. pantanal and suggests the existence of a simple ancestral system with morphologically undifferentiated chromosomes.

Cytogenetic analysis of Lagria villosa (Coleoptera, Tenebrionidae): emphasis on the mechanism of association of the Xy(p) sex chromosomes.

The Xyp 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 Xyp lumen. It was also intended to characterize L. villosa cytogenetically. The analysis of meiotic cells showed 2n = 18 = 16+Xyp for males and 2n = 18 = 16+XX in females and the meiotic formula was 2n = 8II+Xyp. The C-banding showed blocks of pericentromeric heterochromatin in all chromosomes except in the yp 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.

Chromosomal organization of repetitive DNA in Sorubim lima (Teleostei; Pimelodidae).

Interspaced repetitive DNA elements and segmental duplications have been extensively analyzed in fishes through physical chromosome mapping methods, providing a better comprehension of the structure and organization of the genome of this group. In order to contribute to this scenario, a sequence integration study of different classes of repetitive DNA with high resolution physical chromosome mapping was performed in Sorubim lima. Fluorescence in situ hybridization (FISH) and fiber-FISH with probes for 18S and 5S rRNA genes, TTAGGGn sequence and non-LTR retrotransposon family members Rex1, Rex3 and Rex6 showed that non-LTR elements may be dispersed in the chromosome set with relative concentration in heterochromatic regions, as shown by Rex1, or may even intercalate in 45S rDNA and the telomeric sequence, as found for Rex3 and Rex6. These results reinforce the presence of preferential regions of retroelement accumulation and contribute to a better understanding of the genomic organization of some repetitive DNA classes in fishes.

Hermaphroditism can compensate for the sex ratio in the Astyanax scabripinnis species complex (Teleostei: Characidae): expanding the B chromosome study model

Fishes are among the vertebrates with the greatest plasticity with respect to sex determination and differentiation. Astyanax scabripinnis makes up a Neotropical species complex with isolated populations living in river sources and streams and has been used as a model in B chromosome studies. B chromosomes, by definition, are additional to the karyotype and not essential to the carrier organisms. The aim of the present investigation was to determine whether reproductive characteristics and deviation in the sex ratio (1:1) are related to B chromosomes in this species complex. Sample collections were taken from specimens, and gonads were classified based on histological development stages. Fluorescence in situ hybridization using microdissected B chromosome probes was employed for the quantification of individuals with B chromosomes. The sex ratio was estimated and gonadosomatic and hepatosomatic indices were calculated independently for males and females with and without B chromosomes. The occurrence of B chromosomes was related to possible distinct reproductive strategies in the population studied, especially in relation to energetic contribution and gonad development stages. The data suggest that this species complex exhibits functional hermaphroditism and possibly bidirectional sexual inversion. However, hermaphroditism seems to be related to environmental variables, such as temperature and population density, rather than the presence or absence of B chromosomes.

Karyotype analysis of three species of Corydoras (Siluriformes: Callichthyidae) from southern Brazil: rearranged karyotypes and cytotaxonomy

The genus Corydoras comprises a diversity of species with different diploid numbers. We compared cytogenetic data among Corydoras species from different rivers of the Ponta Grossa Arch region in southern Brazil. Corydoras ehrhardti and C. aff. paleatus have a similar karyotype formula and the same diploid number (2n = 44). Corydoras lacrimostigmata has a higher diploid number, with 2n = 58 chromosomes. Fluorescence in situ hybridization using 5S and 18S ribosomal DNA probes suggests that these ribosomal DNA sequences are involved in chromosomal rearrangements in these Corydoras species. 5S rDNA is a chromosomal marker that is considered to be unique to the species analyzed in this study. Signals of interstitial telomeric sites are seen in a chromosome pair of C. lacrimostigmata, suggesting chromosomal rearrangements via fusions or translocations. This study revealed that C. ehrhardti and C. aff. paleatus have exclusive chromosomal markers associated with chromosome differentiation, which we speculate to prevent genetic introgression.

Evolution of trans-Andean endemic fishes of the genus Cheirodon (Teleostei: Characidae) are associated with chromosomal rearrangements

BackgroundAmong Neotropical fishes, the family Characidae is highly diverse and speciose and its taxonomy is not completely resolved. In Chile, the family is represented by five species, all within the genus Cheirodon, of which C. pisciculus, C. galusdae, C. kiliani, and C. australe are endemic, while C. interruptus is introduced. We compared chromosomal markers in order to appreciate the taxonomy and evolution of these trans-Andean fishes.ResultsThe specimens were photographed in stereomicroscope to observe the ventral protrusive teeth and cusps for morphological analysis and species identification. All of the species analysed had equally diploid chromosome number 2nu2009=u200950, with karyotypes dominated by high number of acrocentric chromosomes as compared to those of other members of Cheirodontinae. The distribution of heterochromatin was inconspicuous and was similar in all the species. The number of active NORs (nucleolus organizer regions) was polymorphic, with the greater number of them in C. kiliani and C. galusdae. The location of 5S and 18S rDNA ranged in number and position, showing two sites in different chromosomes. The fluorescent in situ hybridization with telomeric probe did not reveal interstitial sites in all analysed species.ConclusionsThe comparative analysis of karyotypes and morphological markers revealed a biogeographic pattern of distribution, with the species that occur in the southern region forming one group and those in central and northern Chile forming another.