Heterochromatin base pair composition and diversification in holocentric chromosomes of kissing bugs (Hemiptera, Reduviidae)

The subfamily Triatominae (Hemiptera, Reduviidae) includes 150 species of blood-sucking insects, vectors of Chagas disease or American trypanosomiasis. Karyotypic information reveals a striking stability in the number of autosomes. However, this group shows substantial variability in genome size, the amount and distribution of C-heterochromatin, and the chromosome positions of 45S rDNA clusters. Here, we analysed the karyotypes of 41 species from six different genera with C-fluorescence banding in order to evaluate the base-pair richness of heterochromatic regions. Our results show a high heterogeneity in the fluorescent staining of the heterochromatin in both autosomes and sex chromosomes, never reported before within an insect subfamily with holocentric chromosomes. This technique allows a clear discrimination of the heterochromatic regions classified as similar by C-banding, constituting a new chromosome marker with taxonomic and evolutionary significance. The diverse fluorescent patterns are likely due to the amplification of different repeated sequences, reflecting an unusual dynamic rearrangement in the genomes of this subfamily. Further, we discuss the evolution of these repeated sequences in both autosomes and sex chromosomes in species of Triatominae.

Karyotype differentiation of four Cestrum species (Solanaceae) revealed by fluorescent chromosome banding and FISH

The karyotypes of four South American species of Cestrum (C. capsulare, C. corymbosum, C. laevigatum and C. megalophylum) were studied using conventional staining, C-CMA/DAPI chromosome banding and FISH with 45S and 5S rDNA probes. The karyotypes showed a chromosome number of 2n = 2x = 16, with metacentric chromosomes, except for the eighth submeta- to acrocentric pair. Several types of heterochromatin were detected, which varied in size, number, distribution and base composition. The C-CMA+ bands and 45S rDNA were located predominantly in terminal regions. The C-CMA+/DAPI+ bands appeared in interstitial and terminal regions, and the C-DAPI+ bands were found in all chromosome regions. The 5S rDNA sites were observed on the long arm of pair 8 in all species except C. capsulare, where they were found in the paracentromeric region of the long arm of pair 4. The differences in band patterns among the species studied here, along with data from other nine species reported in the literature, suggest that the bands are dispersed in an equilocal and non-equilocal manner and that structural rearrangements can be responsible for internal karyotype diversification. However, it is important to point out that the structural changes involving repetitive segments did not culminate in substantial changes in the general karyotype structure concerning chromosome size and morphology.

Distribution of a Ty3/gypsy-like retroelement on the A and B-chromosomes of Cestrum strigilatum Ruiz & Pav. and Cestrum intermedium Sendtn. (Solanaceae)

Retroelements are a diversified fraction of eukaryotic genomes, with the Ty1/copia and Ty3/gypsy groups being very common in a large number of plant genomes. We isolated an internal segment of the Ty3/gypsy retroelement of Cestrum strigilatum (Solanaceae) using PCR amplification with degenerate primers for a conserved region of reverse transcriptase. The isolated segment (pCs12) was sequenced and showed similarity with Ty3/gypsy retroelements of monocotyledons and dicotyledons. This segment was used as probe in chromosomes of C. strigilatum and Cestrum intermedium. Diffuse hybridization signals were observed along the chromosomes and more accentuated terminal signals in some chromosome pairs, always associated with nucleolus organizer regions (NORs). The physical relationship between the hybridization sites of pCs12 and pTa71 ribosomal probes was assessed after sequential fluorescence in situ hybridization (FISH). Hybridization signals were also detected in the B chromosomes of these species, indicating an entail among the chromosomes of A complement and B-chromosomes.

Karyotype differentiation of four Cestrum species ( Solanaceae ) based on the physical mapping of repetitive DNA

We studied the karyotypes of four Brazilian Cestrum species (C. amictum, C. intermedium, C. sendtnerianum and C. strigilatum) using conventional Feulgen staining, C-Giemsa and C-CMA3/DAPI banding, induction of cold-sensitive regions (CSRs) and fluorescent in situ hybridization (FISH) with rDNA probes. We found that the karyotypes of all four species was 2n = 2x = 16, with, except for the eighth acrocentric pair, a predominance of meta- and submetacentric chromosomes and various heterochromatin classes. Heterochromatic types previously unreported in Cestrum as neutral C-CMA3(0)/DAPI0 bands, CMA3+ bands not associated with NORs, and C-Giemsa/CSR/DAPI- bands were found. The heterochromatic blocks varied in size, number, position and composition. The 45S rDNA probe preferentially located in the terminal and subterminal regions of some chromosomes, while 5S rDNA appeared close to the centromere of the long arm of pair 8. These results suggest that karyotype differentiation can occur mainly due to changes in repetitive DNA, with little modification in the general composition of the conventionally stained karyotype.

Genetic variability of pre and post-fragmentation cohorts of Aspidosperma polyneuron Muell. Arg. (Apocynaceae)

O método de RAPD foi usado para acessar a variabilidade genética em Aspisdosperma polyneuron, uma árvore tropical de vida longa e idade reprodutiva tardia, e muito importante na Floresta Atlântica. Amostras foram coletadas em seis fragmentos florestais na região da cidade de Londrina (Sul do Brasil), uma paisagem fragmentada na década de 30. O perfil de RAPD foi analisado em adultos (pré-fragmentação, >300 anos) e plântulas (pós-fragmentação, <<50 anos). Os resultados mostram uma queda no polimorfismo genético em gerações pós-fragmentação nos pequenos fragmentos e alta diversidade genética dentro das populações. A distribuição da diversidade genética sugere o estabelecimento dos fragmentos como reservas protegidas, e a transferência de plântulas entre os fragmentos para a conservação de A. polyneuron.