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

Reproductive Aspects of Chagas Disease Vectors: Evidence of Transcriptional Activity during the Nucleolar Persistence Phenomenon in the Spermatogenesis of Triatomines

The subfamily Triatominae currently consists of 154 species, most of them being of great importance for public health because they are considered potential vectors of the protozoan Trypanosoma cruzi, the etiologic agent of Chagas disease. In addition to their epidemiological importance, these insects are considered important biological models for cell studies because they have peculiar characteristics in their cells, for example, persistence of the nucleolus during spermatogenesis. This phenomenon is characterized by the presence of the nucleolus or nucleolar corpuscles during all phases of meiosis. To date, all knowledge is restricted to the study of the presence/absence of the nucleolus during the triatomine meiosis, so the present work aimed to analyze if this persistent nucleolar material has transcriptional activity. Analysis of the meiotic metaphases of Rhodnius montenegrensis and Panstrongylus megistus by using fluorochrome acridine orange made it possible to characterize the presence of RNA in the nucleolar material. Thus, it was demonstrated, for the first time, that the persistent nucleolar material during triatomine meiosis is transcriptionally active, supporting the hypothesis of the relationship between nucleolar persistence during meiosis of these insects and the formation of the chromoid body, an organelle responsible for the support of all transcriptional activities during spermiogenesis.

Nucleolar Persistence: Peculiar Characteristic of Spermatogenesis of the Vectors of Chagas Disease (Hemiptera, Triatominae)

All species of triatomines are considered potential vectors of Chagas disease and the reproductive biology of these bugs has been studied by different approaches. In 1999, nucleolar persistence during meiosis was observed in the subfamily for the first time. Recently, it has been observed that all species within the genus Rhodnius exhibit the same phenomenon, suggesting that it may be a synapomorphy of the triatomines. Thus, this article aims to analyze the nucleolar behavior during spermatogenesis of 59 triatomine species. All analyzed species exhibited nucleolar persistence during meiosis. Recently, it has been suggested that nucleolar persistence may be fundamental for the spermatogenesis of these vectors, since it is related to the formation of the chromatoid body. Therefore, we emphasize that this phenomenon is a peculiarity of the Triatominae subfamily and that further studies are required to analyze whether the nucleolar material that persists is active.

Chromosomal characteristics and distribution of constitutive heterochromatin in the Matogrossensis and Rubrovaria subcomplexes

Since 1966 the triatomines were grouped in complexes and specific subcomplexes. Although the complex and subcomplexes not have taxonomic importance, should be monophyletic groups and cytogenetic tools have proved to be of great importance to characterize these species groupings. Based on this, this paper aims to describe the chromosomal characteristics and heterochromatic pattern of Matogrossensis and Rubrovaria subcomplexes, in order to contribute to the taxonomic and evolutionary relationships of these vectors. In this study, at least three males from each species (Triatoma baratai, Triatoma costalimai, Triatoma guazu, Triatoma jurbergi, Triatoma matogrossensis, Triatoma vandae, Triatoma williami, Triatoma carcavalloi, Triatoma circummaculata, Triatoma klugi, Triatoma pintodiasi and Triatoma rubrovaria) were analyzed by means analyzed by means of cytogenetic techniques of C-banding. All species showed the same cytogenetic characteristics: 22 chromosomes, low variation in the size of autosomes, sex chromosome Y larger than X, initial prophase composed of only one heterochromatic chromocenter formed by the sex chromosomes X and Y (except for T. pintodiasi that presented the sex chromosomes individualized during all stages of prophase) and presence of constitutive heterochromatin restricted to sex chromosome Y. These characteristics, although common to Matogrossensis and Rubrovaria subcomplexes allow to distinguish these species of species grouped in most of South America subcomplexes, as Brasiliensis, Maculata, Sordida and Insfestans. Thus, the cytogenetic analysis was of extreme importance to differentiate both subcomplexes of the other subcomplexes of South America. However, probably due to evolutionary proximity existing between these subcomplexes was not possible to observar species differences that make up the Matogrossensis subcomplex of the Rubrovaria subcomplex. Therefore, we emphasize that new comparative analyzes, as experimental hybrid crosses and molecular cytogenetic analysis are necessary to clarify the evolutionary relationship between these important subcomplexes of vectors.

Cytogenetics analysis and testis morphology of aquatic species of the families Belostomatidae, Gelastocoridae, Gerridae, Notonectidae, and Veliidae (Heteroptera)

The Heteroptera have holocentric chromosomes with kinetic activity restricted to the end of chromosomes. The first meiotic division is reductional for the autosomes and equational for the sexual. Only a few species of this suborder have been analyzed. In this study, we observed the morphologies of the testes of the Heteroptera species Belostoma anurum (Herrich-Schäffer, 1948), Belostoma micantulum (Stal, 1858), Gelastocoris angulatus (Melin, 1929), Gelastocoris flavus flavus (Guérin-Méneville, 1844), Rheumatobates crassifemur crassifemur (Esaki, 1926), Buenoa amnigenus (White, 1879), Buenoa unguis (Truxal, 1953), Martarega brasiliensis (Truxal, 1949), Martarega membranácea (White, 1879), Martarega uruguayensis (Berg, 1883), Rhagovelia tenuipes (Champion, 1898) and Rhagovelia zela (Drake, 1959). We found that the testes of these species can be round, round/spiral, or elongated/spiral. The size of the prophase I cells was found to vary, with the smallest ones being detected in B. micantulum and Rha. zela, the largest in G. f. flavus, and ones of intermediate size in R. c. crassifemur and M. brasiliensis. With respect to the chromosome complement, we verified the presence of 2n =  16: (14A+XY, B. micantulum and G. angulatus), 21: (20A+X0, R. c. crassifemur), 23: (22A+X0, Rha. zela and Rha. tenuipes), 25: (24A+X0, Bu. amnigenus and Bu. unguis; 22A+2m+X0, M. membranacea), 27: (24A+2m+X0, M. brasiliensis and M. uruguayensis), 29: (26A+X1X2Y, B. anurum), and 35: (30A+X1X2X3X4Y, G. f. flavus). We found that the features of spermatogenesis in these species are similar to those of other previously described Heteroptera species, differing only in testicular morphology, chromosome number, and sex chromosome system.

Meiotic behavior of 18 species from eight families of terrestrial heteroptera

Insects of the suborder Heteroptera are known for their odor, for being pests, or for being disease carriers. To gain better insight into the cytogenetic characteristics of heteropterans, 18 species of terrestrial Heteroptera belonging to eight families were studied. The presence of heteropycnotic corpuscles during prophase I, terminal or interstitial chiasmas, telomeric associations between chromosomes, ring disposals of autosomes during metaphase, and late migrations of the sex chromosomes during anaphase were analyzed. These features showed identical patterns to other species of Heteroptera previously described in the literature. Another studied characteristic was chromosome complements. The male chromosome complements observed were 2n = 12 chromosomes [10A + XY, Galgupha sidae (Amyot & Serville) (Corimelaenidae) and Pachycoris torridus (Scopoli) (Scutelleridae)]; 2n = 13 [10A + 2m + X0, Harmostes serratus (Fabricius), Harmostes apicatus (Stål), Jadera haematoloma (Herrich-Schaeffer), Jadera sanguinolenta (Fabricius), Jadera sp. (Rhopalidae)], and Neomegalotomus parvus (Westwood) (Alydidae); 2n = 13 [12A + X0, Stenocoris furcifera (Westwood) (Alydidae); 2n = 14 [12A + XY, Dictyla monotropidia (Stål) (Tingidae)]; 2n = 19 [18A + X0, Acanonicus hahni (Stål) (Coreidae)]; 2n = 21 [18A + 2m + X0, Acanthocephala sp. (Dallas) (Coreidae)]; 2n = 27 [24A + 2m + X0, Anisoscelis foliacea marginella (Dallas) (Coreidae)]; 2n = 18 [16A + XY, Oncopeltus fasciatus (Dallas) (Lygaeidae)]; 2n = 17 [14A + X1X2Y, Oxycarenus hyalinipennis (Costa) (Lygaeidae)]; 2n = 16 [12A + 2m + XY, Pachybrachius bilobatus (Say) (Lygaeidae)]; 2n = 26 [24A + XY, Atopozelus opsinus (Elkins) (Reduviidae)]; and 2n = 27 [24A + X1X2Y, Doldina carinulata (Stål) (Reduviidae)]. The diversity of the cytogenetic characteristics of Heteroptera was reflected in the 18 studied species. Thus, this study extends the knowledge of these characteristics, such as the variations related to chromosome complements, sex chromosome systems, and meiotic behavior.

Nucleolar persistence during spermatogenesis of the genus Rhodnius (Hemiptera, Triatominae)

The Triatominae subfamily is comprised of 18 genera and six tribes. The tribe Rhodniini is comprised of two genera (Rhodnius and Psammolestes). Nucleolar persistence is defined by the presence of the nucleolus or nucleolar corpuscles during the meiotic metaphase. To date, this phenomenon has been described for 13 species of triatomine that are included in the genera Triatoma, Rhodnius, and Panstrongylus. Thus, because the phenomenon of nucleolar persistence has been described in only two species of the genus Rhodnius, we have analyzed the nucleolar behavior during spermatogenesis of eight species of the genus Rhodnius (R. colombiensis, R. montenegrensis, R. nasutus, R. neglectus, R. neivai, R. pictipes, R. prolixus, and R. robustus), with a focus on nucleolar persistence. By means of cytogenetic analysis with silver ions, nucleolar behavior during spermatogenesis is described in the eight species of Rhodnius analyzed. In all of them nucleolar behavior was similar and the phenomenon of nucleolar persistence was often observed. Therefore, we confirm nucleolar persistence as a peculiarity of the genus Rhodnius. However, it is emphasized that new cytogenetic analysis should be performed in the Triatominae subfamily, more specifically among the 15 genera that do not exhibit the nucleolar behavior described, in order to assess whether this phenomenon is truly a synapomorphy of these hematophagous insects.

Analysis of spermiogenesis like a tool in the study of the triatomines of the Brasiliensis subcomplex

The specific identification and systematic of triatomines have been based fundamentally on morphological observations. These organisms are classified into complexes and specific subcomplexes, principally for morphological parameters and geographical disposition. The use of cytogenetic analyzes has been represented as a tool in systematic and taxonomy of triatomines. Thus, the present work, through the analysis of spermiogenesis, aims to characterize this stage of spermatogenesis in triatomines little studied, and especially to compare it among the species Triatoma lenti and T. sherlocki, to assist in the diagnosis of differentiation of these insects. The presence of the heteropyknotic corpuscle is shown as a diagnostic tool to differentiate T. sherlocki and T. lenti, since it is absent in T. lenti. The analysis of the spermiogenesis in T. sherlocki also allowed us to address morphological differences between elongating cells, which were relatively smaller and more filamentous when compared to T lenti. Furthermore, the flagellum was observed in all stages of cell differentiation and elongation. This structure, which helps in the locomotion of the sperm, is hardly observed in cytogenetic analysis, especially throughout spermiogenesis. Thus, although other comparative approaches should be taken, this paper allowed emphasizing the analysis of spermiogenesis as an important cytotaxonomic tool that assists in the differentiation of morphologically related species, such as T. lenti and T. sherlocki.

Spermatogenesis of Zaprionus indianus and Zaprionus sepsoides (Diptera, Drosophilidae): Cytochemical, structural and ultrastructural characterization

Zaprionus indianus is a drosophilid native to the Afrotropical region that has colonized South America and exhibits a wide geographical distribution. In contrast, Z. sepsoides is restricted to certain African regions. The two species differ in the size of their testes, which are larger in Z. indianus than in Z. sepsoides. To better understand the biology and the degree of differentiation of these species, the current study evaluated spermatogenesis in males of different ages by conventional staining techniques and ultrastructural analysis. Spermatogenesis and the ultrastructure of spermatozoa were similar in the two species, and the diploid number was confirmed to be 2n = 12. A greater number of spermatozoa were observed in young Z. indianus (1-3 days old) compared to Z. sepsoides males, which showed a higher frequency of cells at the early stages of spermatogenesis. The head of the sperm was strongly marked by silver staining, lacto-acetic orcein and the Feulgen reaction; the P.A.S. reaction revealed glycogen granules in the testes of both species. Both species presented similar arrangement of microtubules (9+9+2), two mitochondrial derivatives of different size and 64 spermatozoa per bundle. Such similarity within the genus Zaprionus with other species of Drosophila, indicates that these structures are conserved in the family Drosophilidae. The differences observed the number and frequency of sperm cells in the early stages of spermatogenesis, between the young males of Z. indianus and Z. sepsoides, are features that may interfere with reproductive success and be related to the invasive potential of Z. indianus.

Cytogenetic evidence for de novo synthesis of rRNA and involvement of nucleolar material in the organization of cell structures during spermiogenesis of Chariesterus armatus (Heteroptera, Coreidae)

The nucleolar material of Chariesterus armatus was analyzed during spermiogenesis in cell preparations impregnated with silver nitrate. Nucleolar corpuscles were observed in spermatids at the beginning of the process, showing that this organoid is also maintained after meiosis. In addition, nucleoli were seen in the round spermatids connected to the X-chromosome (bearer of the nucleolar organizer in C. armatus), indicating de novo synthesis of nucleolar material. This differs from the reorganization of ribosomal granules, transported from meiotic spermatocytes to round spermatids, where they would support protein synthesis, which is reported for other species. We also observed connections of nucleolar corpuscles to the nuclear membrane regions where the tail and the acrosome will be formed, suggesting close involvement of the nucleolar material in the formation of these structures. In addition to the nucleolar bodies, we detected silver-positive structures, which will require new approaches to clarify their role. One of these structures, observed in the cytoplasm, appears to correspond to the chromatoid body, which has been found in several organisms, but is still poorly understood; another is a complex structure to which the tail appears to be connected. We conclude that C. armatus is an appropriate model for understanding not only the synthesis of rRNA in the spermiogenesis, but also the functional meaning of the close relationship of nucleolar material with other structures during this process.