Complex meiotic configuration of the holocentric chromosomes: the intriguing case of the scorpion Tityus bahiensis

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Cytogenetic studies on holocentric chromosomes of five species of triatomines (Heteroptera: Reduviidae)

The chromosome number and meiotic cycle of triatomines were investigated. All five species presented the same diploid chromosome number, 2n = 22 (20A + XY in the male). Phylogenetic relationships based on chromosomal evidence and C-banded karyotypes in the subfamily are discussed. It is suggested that differences in DNA content are mainly due to variations in the amount of C-heterochromatin, which may be interpreted as loss and/or gain of C-regions. This interpretation is supported by the presence of meiotic and mitotic chromocentres which facilitate the transfer of C-positive material.

Cytogenetic study of holocentric chromosomes in three species of triatomines (Heteroptera, Reduvidae)

In the present work, spermatogenesis was analyzed in 3 species of the genus Triatoma (T. platensis, T. proctata, T. tibiamaculata). Lacto-acetic orcein staining was used in order to investigate chromosomal meiotic behavior of these species. It allowed the identification of the T. tibiamaculata karyotype (20, X 1X 2Y), the observation that in T. protacta doesn't occur late migration of sexual chromosomes and corroborated knowledgments about holocentric chromosome nature.

Localization of rDNA sites in holocentric chromosomes of three species of triatomines (Heteroptera, Triatominae).

Chromatin organization in the holocentric chromosomes of three triatomines species was cytologically studied by fluorescent in situ hybridization with a 45S rDNA probe of Drosophila melanogaster to localize ribosomal genes. In Triatoma tibiamaculata, metaphases I showed telomeric highlights in a single, larger bivalent. In T. protacta, hybridization was detected in one of the telomeres of an autosomal chromosome. In T. platensis, there were highlights in a single, smaller chromosome (X chromosome). The results obtained did not agree with the expected localization of rDNA genes in the sex chromosomes of triatomines, as demonstrated by silver impregnation, and suggest that the chromosome reorganization that occurred in this group during evolution may be a more important mechanism involved in rDNA distribution.

Differential characterization of holocentric chromosomes in triatomines (Heteroptera, Triatominae) using different staining techniques and fluorescent in situ hybridization

A comparative study of holocentric chromosomes in the triatomine species Panstrongylus megistus, Rhodnius pallescens and Triatoma infestans was carried out in order to characterize heterochromatin, rDNA active sites and nucleolar proteins. Cytological preparations of seminiferous tubules were stained by silver impregnation, C banding, fluorochromes CMA 3/DA and DAPI/DA, and fluorescent in situ hybridization (FISH) with Drosophila melanogaster 28S rDNA probe. Our results showed interesting aspects of the organization of chromatin and chromosomes in the meiotic cells of these insects. In R. pallescens, sex chromosomes (X, Y) were distinct from autosomes, when submitted to silver impregnation, C banding, CMA 3 staining, and FISH, confirming that these chromosomes bear nucleolar organizer regions (NORs). In P. megistus, two of the three sex chromosomes were CMA 3/DAPI-; at early meiotic prophase and at diakinesis, silver impregnation corresponded with FISH signals, indicating that in this species, two chromosomes (probably a sex chromosome and an autosome) bear NORs. In T. infestans, silver nitrate and FISH also stained corresponding areas on meiotic chromosomes. Our data suggest that in triatomines, in general, the number and location of NORs are species-specific. These regions may be considered important chromosome markers for comparative studies to improve the understanding of evolutionary mechanisms in these hematophagous insects. ©FUNPEC-RP.

Karyotype and spermatogenesis in Triatoma lenti (Hemiptera: Triatominae), a potential Chagas vector

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Spermatogenesis and nucleolar activity in Triatoma klugi (Triatomine, Heteroptera)

Triatoma klugi is a Chagas disease vector in the Rio Grande do Sul State. Triatominae chromosomes are holocentric and sex chromosomes segregation is post-reductional. In this paper we describe the karyotype of male T. klugi and a meiotic analysis including the nucleolar behavior during spermatogenesis. Testis cells were analyzed after lacto-acetic orcein and silver nitrate staining. Two autosomes and the heterochromosomes presented nucleolar activity (Ag-NORs) during diplotene-diakinesis. The analysis of metaphase I and II revealed a karyotype with 2n = 20+XY. In metaphase I a prominent nucleolar mass was observed in the cell periphery and small silver grains were detected in metaphase II. During anaphase, the chromosomes segregated in parallel and a typical holocentric late migration behavior was observed. The restoration of the nucleolus was an important feature in this phase. During telophase nucleolar masses persisted and in early spermiogenesis the spermatids presented a small peripheral mass until elongation. The present study is a contribution to the study of chromatin behavior and nucleolar persistence in meiosis.

Meiotic chromosomes and nucleolar behavior in testicular cells of the grassland spittlebugs Deois flavopicta, Mahanarva fimbriolata and Notozulia entreriana (Hemiptera, Auchenorrhyncha)

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Meiosis, spermatogenesis and nucleolar behavior in the seminiferous tubules of Alydidae, Coreidae and Rhopalidae (Heteroptera) species.

We studied the karyotype, spermatogenesis and nucleolar activity at spermatogenesis in five species of Heteropera: Hyalymenus sp and Neomegalotomus pallescens, Alydidae; Catorhintha guttula and Hypselonotus fulvus, Coreidae; and Niesthrea sidae, Rhopalidae. They showed a red (Alydidae) or orange (Coreidae and Rhopalidae) membrane covering the testes, which consisted of seven testicular lobes, except in N. pallescens, which had only five. All the species had m-chromosomes, an X0 sex chromosome system and 10 (Hyalymenus sp, N. pallescens, and N. sidae), 16 (H. fulvus) or 22 (C. guttula) autosomes. Similar to the other species described to date, all these species showed holocentric chromosomes, interstitial chiasmata in most autosomes, and autosomes dividing reductionally in the first meiotic division and equationally in the second, while sex chromosomes, divided equationally and reductionally in the first and second meiotic divisions, respectively. In addition, we observed that the sex chromosome is heteropycnotic at prophase and that heteropycnotic chromosomal material is found in the nuclei at spermatogenesis; variation in size, shape and location of the nucleolar material occurs during spermatogenesis, denoting a variable degree of activity in the different stages.

Heterochromatin patterns in triatomines of the genus Panstrongylus

Spermatogenesis was analysed by C-banding in two species of triatomines, Panstrongylus megistus and Fl herreri. Both species revealed interstitial and terminal bands in the autosomes, which is a common pattern in Heteroptera. The terminal bands corroborated the hypothesis that in holocentric chromosomes the heterochromatin is preferentially located at the telomere. The sex chromosomes in FI herreri were totally heterochromatic in spermatogenesis, and in P. megistus the X chromosomes alternated between positive and negative banding.

Distribution of 45S and 5S rDNA sites in 23 species of Eleocharis (Cyperaceae)

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Karyotype Conservation in 2 Populations of the Parthenogenetic Scorpion Tityus serrulatus (Buthidae): rDNA and Its Associated Heterochromatin Are Concentrated on Only One Chromosome

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Spermatogenesis and nucleolar behavior in males of aquatic Heteroptera

Aspects of spermatogenesis and nucleolar behavior were analyzed in Brachymetra albinerva, Cylindrostethus palmaris, Halobatopsis platensis, Limnogonus aduncus (Gerridae), Martarega sp (Notonectidae), Rhagovelia whitei, and Rhagovelia sp (Veliidae). The testicles are rounded (Veliidae), elongated (Gerridae) or spiral (Notonectidae) and have a transparent membrane covering them. The complement chromosome was 2n = 23 (22A + X0, L. aduncus and Rhagovelia sp), 25 (24A + X0, B. albinerva and H. platensis), 26 (22A + 2m + XY, Martarega sp), 29 (28A + X0, C. palmaris), or 39 (38A + X0, R. whitei) chromosomes, and the only species with a different sex chromosome system was Martarega sp, which showed an XY system and m-chromosomes. The meiotic behavior of all species was similar: holocentric chromosomes and heteropyknotic material at prophase, interstitial and/or terminal chiasmata, and first reductional division for the autosomes and the reverse for the sex chromosomes. The only difference observed was related to the very large size of Martarega sp cells in all stages of spermatogenesis. With regard to nucleolar behavior, the species did not show differences, except for Martarega sp with larger nucleoli than the other species. The only species in which it was clearly possible to identify the nucleolar organizer region was L. aduncus, in the region of a terminal autosome. It was also confirmed that the telomeric associations do not occur at random. In the other species, specific staining was very discrete, and the nucleolar organizer region location was not at all evident.

Chromosome analysis of two species of sugar cane pests of the genus Mahanarva (Homoptera, Cercopidae)

Studies on the cytogenetics of Homoptera are scarce. Some references in the literature have reported a chromosome number for the genus ranging from n=5 to 19 and 2n=10 to 2n=39 chromosomes. The genus Mahanarva includes two species of agricultural importance as pests of sugar cane culture in Brazil. We report here the first data concerning the chromosome number and morphology of the species Mahanarva fimbriolata and M. posticata. The chromosome number observed for the two species was 2n=19 for males and 2n=20 for females. The sex determining mechanism of these species was of the XX/X0 type (for males and females, respectively), with chromosome X being the smallest in the complement.

Description of the nucleolar activity and karyotype in germinative cell lines of Rhodnius domesticus (Triatominae, Heteroptera)

The purpose of this work was to study the karyotype, spermatogenesis and nucleolar activity at meiosis, in the species Rhodnius domesticus (Heteroptera, Triatominae). The testicular tubules were cytologically prepared by the conventional method of cell crushing and subsequent application of cytogenetic staining techniques with lacto-acetic orcein and silver-ion impregnation. The species under study presented karyotype 2n= 20A+XY, the modal number of the subfamily Triatominae. The chromosomes presented no primary constriction and were therefore characterized as holocentric. It was observed that the sex chromosomes sometimes were located at the periphery, close to the ring formed by autosomes, at first meiotic division. At metaphases II, sex chromosomes were positioned in the center of the autosomal ring, thus evidencing a postreductional behavior. These same chromosomes showed late migration at anaphases and were clearly impregnated with silver-ions, suggesting they bore Nucleolar Organizer Regions. Dispersed nucleolar corpuscles in cytoplasm until telophase II and small dots in spermatids strongly impregnated with silver, could be seen. Thus, it may be inferred that, in triatomines, the nucleolus does not completely disappear but remains in the form of small corpuscles that have a role in cell differentiation.