Autosomal Bivalents Research Articles

C-banding characterization of centric fusion and heterochromatin polymorphisms in the water-hyacinth grasshopper, Cornops aquaticum (Orthoptera: Acrididae)

Abstract The water-hyacinth grasshopper, Cornops aquaticum (Orthoptera: Acrididae), shows a clinal variation for 3 Robertsonian translocation (centric fusion) polymorphisms in the southern extreme of its wide geographical distribution. It is a Neotropical semiaquatic grasshopper that lives, feeds, and lays eggs exclusively on floating plants of the family Pontederiaceae, or water-hyacinths, between 23° N (Southern Mexico) and 35° S (Central Argentina and Uruguay). Given the invasive-species status of Pontederia (formerly Eichhornia) crassipes and the voraciousness of these grasshoppers, they were considered as a potential biological control agent in addition to other natural enemies. We already described the association of the rearrangements with geographical and climatic variables, phenotypic variation, trivalent orientation, effects on recombination, and relationship with microsatellite variability. Here we analyze the distribution of constitutive heterochromatin in 2 populations of C. aquaticum in order to (i) provide consistent markers for a better distinction between all chromosomes, those which are involved in the centric fusions, and those which are not, and (ii) describe possible polymorphisms for C-positive supernumerary segments, given that, on conventional staining analysis, it was frequent to find heteromorphic autosomal bivalents. The cytogenetic analysis allowed us to get a detailed characterization of the constitutive heterochromatin distribution, providing unmistakable chromosome markers of the large, fusion-bearing chromosomes as well as the C-positive, polymorphic supernumerary segments.

Cytological Study of Family Aeshnidae (Odonata: Anisoptera) From India: A Review

ABSTRACT: Cytological review of 59 aeshnid species and cytogenetic investigations on Anax ephippiger, Anax immaculifrons, Anax indicus, Anax nigrofasciatus nigrolineatus, Anax parthenope, Gynacantha subinterrupta of the family Aeshnidae by carbol fuchsin staining and C - banding have been under taken. All the species posses 2n = 27m with X0 - XX sex determination except Anax ephippiger with 2n = 14 + neo XY, resulted by the 13 simultaneous fusions among the autosomes and between autosome and sex chromosome. The structure and behaviour of chromosomes, variation in size of m chromosomes and X chromosome and distribution of C - heterochromatin have been studied and compared among the species. C - bands are mostly present at the terminal regions of autosomal bivalents, while Anax ephippiger and Anax parthenope also possess C - bands at the interstitial and sub-terminal regions of the bivalents. Moreover, sex chromosome and m bivalent show variation in distribution of C-heterochromatin in the species. Out of these, chromosome complement of Anax indicus Lieftinck, 1942 and C - banding on Anax ephippiger and Anax indicus have been investigated for the first time. List of cytologically studied species of family Aeshnidae has been updated to 60 species.

A Brief Review of Meiotic Chromosomes in Early Spermatogenesis and Oogenesis and Mitotic Chromosomes in the Viviparous Lizard Zootoca vivipara (Squamata: Lacertidae) with Multiple Sex Chromosomes

This brief review is focused on the viviparous lizard Zootoca vivipara (Lichtenstein, 1823), of the family Lacertidae, which possesses female heterogamety and multiple sex chromosomes (male 2n = 36, Z1Z1Z2Z2/Z1Z2W, female 2n = 35, with variable W sex chromosome). Multiple sex chromosomes and their changes may influence meiosis and the female meiotic drive, and they may play a role in reproductive isolation. In two cryptic taxa of Z. vivipara with different W sex chromosomes, meiosis during early spermatogenesis and oogenesis proceeds normally, without any disturbances, with the formation of haploid spermatocytes, and in female meiosis with the formation of synaptonemal complexes (SCs) and the lampbrush chromosomes. In females, the SC number was constantly equal to 19 (according to the SC length, 16 SC autosomal bivalents plus three presumed SC sex chromosome elements). No variability in the chromosomes at the early stages of meiotic prophase I, and no significant disturbances in the chromosome segregation at the anaphase-telophase I stage, have been discovered, and haploid oocytes (n = 17) at the metaphase II stage have been revealed. There should be a factor/factors that maintain the multiple sex chromosomes, their equal transmission, and the course of meiosis in these cryptic forms of Z. vivipara.

Teflon promotes chromosomal recruitment of homolog conjunction proteins during Drosophila male meiosis.

Meiosis in males of higher dipterans is achiasmate. In their spermatocytes, pairing of homologs into bivalent chromosomes does not include synaptonemal complex and crossover formation. While crossovers preserve homolog conjunction until anaphase I during canonical meiosis, an alternative system is used in dipteran males. Mutant screening in Drosophila melanogaster has identified teflon (tef) as being required specifically for alternative homolog conjunction (AHC) of autosomal bivalents. The additional known AHC genes, snm, uno and mnm, are needed for the conjunction of autosomal homologs and of sex chromosomes. Here, we have analyzed the pattern of TEF protein expression. TEF is present in early spermatocytes but cannot be detected on bivalents at the onset of the first meiotic division, in contrast to SNM, UNO and MNM (SUM). TEF binds to polytene chromosomes in larval salivary glands, recruits MNM by direct interaction and thereby, indirectly, also SNM and UNO. However, chromosomal SUM association is not entirely dependent on TEF, and residual autosome conjunction occurs in tef null mutant spermatocytes. The higher tef requirement for autosomal conjunction is likely linked to the quantitative difference in the amount of SUM protein that provides conjunction of autosomes and sex chromosomes, respectively. During normal meiosis, SUM proteins are far more abundant on sex chromosomes compared to autosomes. Beyond promoting SUM recruitment, TEF has a stabilizing effect on SUM proteins. Increased SUM causes excess conjunction and consequential chromosome missegregation during meiosis I after co-overexpression. Similarly, expression of SUM without TEF, and even more potently with TEF, interferes with chromosome segregation during anaphase of mitotic divisions in somatic cells, suggesting that the known AHC proteins are sufficient for establishment of ectopic chromosome conjunction. Overall, our findings suggest that TEF promotes alternative homolog conjunction during male meiosis without being part of the final physical linkage between chromosomes.

Segregation of the univalent X chromosome in the wide-footed treehopper Enchenopa latipes (Say 1824)

In metaphase I, autosomal bivalents align on the metaphase plate, while naturally-occurring univalent sex chromosomes can display a number of different behaviours depending on cellular conditions. Here we describe the behaviour of the univalent X chromosome in the wide-footed treehopper Enchenopa latipes (Say 1824). We confirm the chromosome number and sex determination method for this species, and that males possess a univalent X chromosome. We show that the univalent X chromosome forms a bipolar attachment to the spindle in metaphase I, and then segregates intact toward one spindle pole in late anaphase I (long after autosomes have initiated poleward movement). Movement of the univalent toward one pole is associated with loss of microtubule connections toward the opposite spindle pole.

Karyotypic Studies on Seven Chlorocyphid Species Based on C-Bands, AgNOR’s and AT-GC Regions with Review of the Hitherto Cytologically Examined Data of Family Chlorocyphidae (Odonata: Zygoptera)

Cytogenetic characterization on seven species of family Chlorocyphidae by carbol-fuchsin staining, Cbanding, silver nitrate staining and DAPI and CMA3 staining has been done. Among these, Aristocypha quadrimaculata, A. trifasciata, Heliocypha biforata, H. bisignata, H. perforate and Paracypha unimaculata are of subfamily Rhinocyphinae and Libellago lineata is of subfamily Libellagininae. All the species of subfamily Rhinocyphinae possess n=12m, which is the type number of the subfamily and complement is characterized by the presence of one large autosomal bivalent, originated by the autosomal fusion. But L. lineata with n= 13m is the only species of subfamily Libellagininae. C-bands and NOR’s are mostly detected on terminal ends of autosomal bivalents in all the 7 species and also at interstitial regions of large bivalent. X chromosome is entirely C-positive in all the species, while it is NOR-positive in both the species of genus Aristocypha, P. unimaculata, H. perforata, and shows NOR on one terminal end in H. bisignata and L. lineata. m bivalent is C-negative in H. biforata and in both the species of genus Aristocypha, while shows C-bands on both the terminals in H. perforata, P. unimaculata and L. lineata, whereas possesses C-band on one terminal end in H. bisignata. m bivalent shows NOR on one terminal end in P. unimaculata and L. lineata, while NOR-negative in all the species of genera Aristocypha and Heliocypha. Complement of all the species shows bright DAPI and weak CMA3.signals which depicts the presence of more AT rich regions than GC regions.

DNA Environment of Centromeres and Non-Homologous Chromosomes Interactions in Mouse.

Although the pericentromeric regions of chromosomes that are enriched in tandemly repeated satellite DNA represent a significant part of eukaryotic genomes, they remain understudied, which is mainly due to interdisciplinary knowledge gaps. Recent studies suggest their important role in genome regulation, karyotype stability, and evolution. Thus, the idea of satellite DNA as a junk part of the genome has been refuted. The integration of data regarding molecular composition, chromosome behaviour, and the details of the in situ organization of pericentromeric regions is of great interest. The objective of this work was a cytogenetic analysis of the interactions between pericentromeric regions from non-homologous chromosomes in mouse spermatocytes using immuno-FISH. We analysed two events: the associations between centromeric regions of the X chromosome and autosomes and the associations between the centromeric regions of the autosomal bivalents that form chromocenters. We concluded that the X chromosome forms temporary synaptic associations with different autosomes in early meiotic prophase I, which can normally be found until the pachytene–diplotene, without signs of pachytene arrest. These associations are formed between the satellite-DNA-rich centromeric regions of the X chromosome and different autosomes but do not involve the satellite-DNA-poor centromeric region of the Y chromosome. We suggest the hypothetical model of X chromosome competitive replacement from such associations during synaptic correction. We showed that the centromeric region of the X chromosome in association remains free of γH2Ax-dependent chromatin inactivation, while the Y chromosome is completely inactivated. This finding highlights the predominant role of associations between satellite DNA-rich regions of different chromosomes, including the X chromosome. We suppose that X-autosomal transient associations are a manifestation of an additional synaptic disorder checkpoint. These associations are normally corrected before the late diplotene stage. We revealed that the intense spreading conditions that were applied to the spermatocyte I nuclei did not lead to the destruction of stretched chromatin fibers of elongated chromocenters enriched in satellite DNA. The tight associations that we revealed between the pericentromeric regions of different autosomal bivalents and the X chromosome may represent the basis for a mechanism for maintaining the repeats stability in the autosomes and in the X chromosome. The consequences of our findings are discussed.

CHROMOSOME CHARACTERIZATION OF FOUR CALOPTERYGID DAMSELFLIES WITH CYTOGENETIC REVIEW OF FAMILY CALOPTERYGIDAE (ODONATA: ZYGOPTERA)

Taxonomically, in family Calopterygidae, 183 species under 21 genera have been reported worldwide. Out of these, cytogenetic data pertains to only 22 species which is only 12% of the known species. In India, 9 species under 6 genera are present, while only 2 species has been studied cytogenetically. The present study has been conducted to linearly characterize the chromosomes of 4 species (Matrona nigripectus, Neurobasis chinensis, Vestalis apicalis and Vestalis gracilis) of family Calopterygidae by conventional staining, C-banding, silver nitrate staining and sequence-specific staining and also compiled the cytogenetic data of the family. The species were collected from Meghalaya, Goa, Kerala, Himachal Pradesh states of India. All the species possesses 2n=25m as the diploid chromosome number with XO-XX sex determination except Neurobasis chinensis with 2n=23, characterized by the presence of two equal sized large autosomal bivalents originated by the autosome fusion. C-banding and silver nitrate staining results depict the presence of C-bands and NOR’s on the terminal positions of autosomal bivalents, while X chromosome and m bivalent show variation in distribution of C-heterochromatin and NOR’s. Sequence-specific staining represents the complement of all the species as AT-rich due to more DAPI bright signals. All the cytogenetically studied species have been catalogued including the presently studied species and the list has been updated to 23 species

Genetic implications of a biological invasion: Chromosomal and DNA barcode monomorphism in Old World populations of Colorado potato beetle Leptinotarsa decemlineata (Coleoptera: Chrysomelidae)

Once introduced into new area, invasive species can be expected to have low genetic diversity due to the founder effect. Here we tested this prediction using cytogenetic and molecular analysis of Armenian and Belarusian populations of Colorado potato beetle Leptinotarsa decemlineata (Say, 1824) and by comparing the results with those of native (North America) and those introduced into Europe. This revealed that the karyotype of males from Armenia and Belarus is remarkably conserved with 2n = 35 (34 + X0), n = 17AA + X0; and includes a pair of large acrocentric chromosomes. Thus, these populations belong to the so-called acrocentric chromosome race of the Colorado potato beetle. At diakinesis there are clearly visible argentophilic signals, probably NORs (the nucleolus organizer regions) present on some autosomal bivalents, while the X chromosome was homogenously argentophilic during different stages of meiosis. C-banding revealed a small amount of constitutive heterochromatin weakly visible in the pericentromeric regions of some chromosomes. Analysis of the DNA-barcode fragment of the gene cytochrome c oxidase subunit I (COI) revealed a single haplotype (we call it "the European haplotype") and lack of inter-population variability in all the samples collected from different locations in Armenia and Belarus. The comparison of our karyological and molecular data with that available in the literature and GenBank shows that all the populations studied from the Old World are monomorphic with respect to karyotype and the mitochondrial DNA-barcode. We assume that (1) the presence of acrocentric chromosomes in the karyotype and (2) the European haplotype of mitochondrial genome are the ancestral states for all populations in the Old World and inherited from the New World invaders who colonized Europe 100 years ago. New World populations are polymorphic with respect to karyotype and mitochondrial genes; however, the European haplotype has not yet been found in America. We believe that in the future it will be found in North America, which will shed light on the origin of populations of this dangerous pest in Eurasia.

Cytogenetic Studies on Three Species of Genus Burmagomphus of Family Gomphidae (Odonata: Anisoptera) from India

Male germ cell chromosomes of Burmagomphus divaricatus, Burmagomphus pyramidalis and Burmagomphus sivalikensis of family Gomphidae have been investigated by using conventional staining, C-banding, silver nitrate staining and sequence specific staining. The species were collected from Punjab and Himachal Pradesh, India. All the species possess the chromosome number 2n = 23 which is the type number of the family. Terminal C bands and NOR’s are present at the autosomal bivalents and X chromosome is C positive and NOR rich in all the three species, while m bivalents show variation in distribution of C- heterochromatin and NOR’s. In the sequence specific staining, whole complement shows bright DAPI signals in B. divaricatus, bright CMA3 signals in B. pyramidalis and both DAPI and CMA3 signals in B. sivalikensis.

First chromosomal analysis in Deinopidae (Araneae) reveals Sex Chromosome System X1X2X3X4, B chromosomes and polymorphism for centric fusion

Here we present the first cytogentic study concerning Deinopidae and their controversial phylogenetic position. This study karyologically analyzed one population of Deinopis biaculeata Simon, 1906 and five populations of Deinopis plurituberculata Mello-Leitão, 1925. The majority of specimens of D. plurituberculata exhibited 2n♂ = 40 and 2n♀ = 44 telocentric chromosomes (however some of them showed B chromosomes, belongs to Aquidauana and Botucatu population). The Deinopis biaculeata and D. plurituberculata meiosis of males showed 18 autosomal bivalents + X1X2X3X4, n = 22 and n = 18, a rare sex chromosome system (SCS) in spiders. Some individuals of D. plurituberculata from the Campo Grande population exhibited 2n♂ = 39 and 2n♀ = 43, with a metacentric chromosome (heterozygotes for centric fusion). The D. plurituberculata males with the rearrangement exhibit diplotenes with 16 autosomal bivalents + 1 autosomal trivalent + X1X2X3X4 and metaphases II with n = 22 (18 telocentric autosomes + X1X2X3X4), n = 21 (16 telocentric autosomes + a metacentric autosome + X1X2X3X4), n = 18 (18 telocentric autosomes) and n = 17 (16 telocentric autosomes + a metacentric autosome). The Ag-NORs (silver impregnation) are terminally located in a pair, coinciding with secondary constriction, which is the most common configuration for Araneae. The relatively high diploid number in Deinopis corroborates phylogenies that place it in a basal position among Entelegynes, in the UDOH grade (Uloboridae, Deinopidae, Oecobiidae and Hersiliidae). Centric fusion in only one population of D. plurituberculata suggests low dispersion capacity of this species and an absence of homozygotes for fusion suggests their low viability or a need to increase the population sampling of D. plurituberculata exhibiting the rearrangement. B chromosomes were detected in D. plurituberculata, with interpopulacional, intrapopulacional and intraindividual numerical variation, with cells presenting 0 - 3 and 0 - 6 B chromosomes in populations of Aquidauana and Botucatu, respectively.

Meiotic synapsis of homeologous chromosomes and mismatch repair protein detection in the parthenogenetic rock lizard Darevskia unisexualis.

Parthenogenetic species of Caucasian rock lizards of the genus Darevksia are important evidence for reticulate evolution and speciation by hybridization in vertebrates. Female-only lineages formed through interspecific hybridization have been discovered in many groups. Nevertheless, critical mechanisms of oogenesis and specifics of meiosis that provide long-term stability of parthenogenetic species are still unknown. Here we report cytogenetic characteristics of somatic karyotypes and meiotic prophase I nuclei in the diploid parthenogenetic species Darevskia unisexualis from the new population "Keti" in Armenia which contains an odd number of chromosomes 2n = 37, instead of the usual 2n = 38. We revealed 36 acrocentric chromosomes and a single metacentric autosomal chromosome, resulting from Robertsonian translocation. Comparative genomic hybridization revealed that chromosome fusion occurred between two chromosomes inherited from the maternal species, similar to another parthenogenetic species D. rostombekowi. To trace the chromosome behaviour in meiosis, we performed an immunocytochemical study of primary oocytes' spread nuclei and studied chromosome synapsis during meiotic prophase I in D. unisexualis based on analysis of synaptonemal complexes (SCs). We found meiotic SC-trivalent composed of one metacentric and two acrocentric chromosomes. We confirmed that the SC was assembled between homeologous chromosomes inherited from two parental species. Immunostaining of the pachytene and diplotene nuclei revealed a mismatch repair protein MLH1 loaded to all autosomal SC bivalents. Possible mechanisms of meiotic recombination between homeologous chromosomes are discussed.

Cytogenetic characterization of five species of genus Coeliccia of family Platycnemididae (Odonata: Zygoptera) using C-banding, silver nitrate staining and sequence specific staining

Cytogenetic characterization of five species of genus Coeliccia of family Platycnemididae has been done by conventional staining, C-banding, silver nitrate staining and sequence specific staining. These species were collected from the localities present in Andretta, Bilaspur (Himachal Pradesh) and Nongkhyllem (Meghalaya), India. All the species possess n = 13 as haploid chromosome number, which is the type number of the family with X0–XX sex determining mechanism except Coeliccia bimaculata with n = 12, originated by the fusion of two autosome pairs as complement is characterized by the presence of one large bivalent. m chromosomes are absent in all the species. Mostly, light/dark terminal C-bands and NOR’s are seen on the autosomal bivalents, while X chromosome shows variations as large terminal C-band on one side of X chromosome is present in all the species except C. renifera, it is C-positive. Moreover, X chromosome possesses terminal NOR on one side in C. chromothorax, while NOR-positive in C. renifera and NOR-negative in C. bimaculata, C. didyma and C. fraseri. In sequence specific staining, autosomal bivalents are homogeneously stained with both DAPI and CMA3 dyes in C. bimaculata, C. renifera and C. chromothorax, while whole chromosome complement of C. didyma is CMA3 bright and C. fraseri is DAPI bright.

Meiotic Chromosomes, Synaptonemal Complexes in a Female Viviparous Lizard (Zootoca vivipara) in Prophase I of Meiosis

In the females of the viviparous lizard Zootoca vivipara (Lichtenstein, 1823) (family Lacertidae) from Northwest Russia (2n = 35: 32A (acrocentric autosomes) + Z1Z2W sex chromosomes), the ovarian lumen germinal vesicles (oocytes), as well as germinal lamina cells, were examined. Chromosome preparations were obtained using the direct method and the method of total oocyte nuclei spreading developed by Dresser and Moses. Chromosome preparations were stained with Giemsa; for visualization of synaptonemal complexes (SCs), total preparations of oocyte nuclei were stained with silver nitrate and DAPI. It was demonstrated that, during oogenesis in the female, primary follicles enter the early stages of the meiotic prophase I (stages from leptotene to diplotene, lampbrush chromosomes are formed). Here, for the first time, total oocyte spreads were obtained and studied. On the basis of light microscopic analysis of the oocyte SCs and taking into account their length in a female with 2n = 35, the SC karyotype is presented, consisting of 19 SC elements, among which 16 SC autosomal bivalents are distinguished. The remaining three SC elements, according to the authors, can be univalents of Z1Z2W sex chromosomes or one WZ1 bivalent and Z2 and B chromosome univalents. As in the SC karyotype of Z. vivipara males, in a female, specific features in the morphology of SC elements of chromosomes 5 and 6 were observed.

MNM and SNM maintain but do not establish achiasmate homolog conjunction during Drosophila male meiosis.

The first meiotic division reduces genome ploidy. This requires pairing of homologous chromosomes into bivalents that can be bi-oriented within the spindle during prometaphase I. Thereafter, pairing is abolished during late metaphase I, and univalents are segregated apart onto opposite spindle poles during anaphase I. In contrast to canonical meiosis, homologous chromosome pairing does not include the formation of a synaptonemal complex and of cross-overs in spermatocytes of Drosophila melanogaster. The alternative pairing mode in these cells depends on mnm and snm. These genes are required exclusively in spermatocytes specifically for successful conjunction of chromosomes into bivalents. Available evidence suggests that MNM and SNM might be part of a physical linkage that directly conjoins chromosomes. Here this notion was analyzed further. Temporal variation in delivery of mnm and snm function was realized by combining various transgenes with null mutant backgrounds. The observed phenotypic consequences provide strong evidence that MNM and SNM contribute directly to chromosome linkage. Premature elimination of these proteins results in precocious bivalent splitting. Delayed provision results in partial conjunction defects that are more pronounced in autosomal bivalents compared to the sex chromosome bivalent. Overall, our findings suggest that MNM and SNM cannot re-establish pairing of chromosomes into bivalents if provided after a chromosome-specific time point of no return. When delivered before this time point, they fortify preformed linkages in order to preclude premature bivalent splitting by the disruptive forces that drive chromosome territory formation during spermatocyte maturation and chromosome condensation during entry into meiosis I.

Evolution of the Sex Chromosomes in Beetles. I. The Loss of the Y Chromosome

In the males of Coleoptera, the most frequent sex chromosome constitution is XY. At metaphase I of meiosis, the X and Y are linked by nucleolar proteins, forming the so-called parachute bivalent (Xy_p), which is assumed to allow the non-synapsed X and Y to segregate correctly at anaphase I. However, X0 males are not exceptional, and we explored the relationships between the X and nucleolar proteins in the absence of the Y chromosome in 6 species belonging to different families/subfamilies. Using C-banding and silver staining, we show that nucleolar proteins always remain in contact with the X until anaphase I. These proteins are generally more abundant than in the Xy_p bivalent, may remain associated with the NOR during diakinesis, and frequently link the X to 1 or 2 autosomal bivalents, which seem to play the same role as the Y. This role may also be played by B chromosomes, which appear to be more frequent in X0 than in XY males. In conclusion, following Y chromosome loss, various strategies using nucleolar proteins have been developed to facilitate the migration of the unique X at meiotic anaphase I.

Alterations in chromosomal synapses and DNA repair in apoptotic spermatocytes of Mus m. domesticus.

We investigated whether apoptotic spermatocytes from the mouse Mus m. domesticus presented alterations in chromosomal synapses and DNA repair. To enrich for apoptotic spermatocytes, the scrotum’s temperature was raised by partially exposing animals for 15 min to a 42ºC water bath. Spermatocytes in initial apoptosis were identified in situ by detecting activated caspase-9. SYCP1 and SYCP3 were markers for evaluating synapses or the structure of synaptonemal complexes and Rad51 and γH2AX for detecting DNA repair and chromatin remodeling. Apoptotic spermatocytes were concentrated in spermatogenic cycle stages III-IV (50.3%), XI-XII (44.1%) and IX-X (4.2%). Among apoptotic spermatocytes, 48% were in middle pachytene, 44% in metaphase and 6% in diplotene. Moreover, apoptotic spermatocytes showed several structural anomalies in autosomal bivalents, including splitting of chromosomal axes and partial asynapses between homologous chromosomes. γH2AX and Rad51 were atypically distributed during pachytene and as late as diplotene and associated with asynaptic chromatin, single chromosome axes or discontinuous chromosome axes. Among apoptotic spermatocytes at pachytene, 70% showed changes in the structure of synapses, 67% showed changes in γH2AX and Rad51 distribution and 50% shared alterations in both synapses and DNA repair.Our results showed that apoptotic spermatocytes from Mus m. domesticus contain a high frequency of alterations in chromosomal synapses and in the recruitment and distribution of DNA repair proteins. Together, these observations suggest that these alterations may have been detected by meiotic checkpoints triggering apoptosis.

New sex-determination system inthe genus Panstrongylus (Hemiptera: Reduviidae) revealed by chromosomal analysis of Panstrongylus lutzi.

BackgroundPanstrongylus lutzi (Neiva & Pinto, 1923) is a triatomine species native to Caatinga habitats in north-eastern Brazil. It is considered an important vector of Chagas disease in this region, presenting high rates of natural infection with Trypanosoma cruzi Chagas, 1909, and readily invading houses by flight. This study describes a previously unknown chromosomal sex system in the genus Panstrongylus based on P. lutzi.MethodsFifth-instar and male adults of P. lutzi originating from municipality of Várzea Alegre, Ceará (Brazil) were analysed. Chromosomal analyses of male meiotic process were done by Giemsa staining.ResultsChromosomal analyses of male meiosis reveal a diploid chromosome number of 24 chromosomes (20 autosomes plus X1X2X3Y). During meiotic prophase I, the sex chromosomes remained close together, forming four heteropycnotic chromocenters in zygotene, and a single chromocenter in pachytene and diplotene. Still at the diplotene stage, each one of the ten autosomal bivalents showed an evident chiasma. In metaphase I, the four sex chromosomes appeared clearly separated. The three X chromosomes were the smallest of the complement and isopycnotic with respect to the Y chromosome. Two bivalents appear larger, whereas the other eight showed no significant difference in size.ConclusionKaryotype analysis of P. lutzi revealed a new sex system in the genus Panstrongylus. This result is of utmost importance to karyosystematics of P. lutzi, and demonstrates the need for further studies of this type in the subfamily Triatominae.

Chromosomal evolution in the pallescens group (Hemiptera, Triatominae).

Rhodnius colombiensis, in conjunction with R. pallescens and R. ecuadoriensis, forms the monophyletic pallescens group. Cytogenetic analyses of these closely related species would further our understanding of the taxonomy and evolution of this group. In this study, R. colombiensis was cytogenetically analyzed, and the results were compared with cytogenetic data from other species of the pallescens group, particularly their chromosomal evolution. We found that this triatomine has heteropycnotic blocks in five autosomal bivalents at both metaphase I and II. The derivation of R. colombiensis from R. pallescens led to significant loss of heteropycnotic and heterochromatic regions (approximately 50%). R. ecuadoriensis is the most differentiated of the group because it has lost all heterochromatin and heteropyknotic blocks in the autosomes. Based on the heteropyknotic and heterochromatic pattern of R. colombiensis and the chromosomal evolution analysis of the pallescens group, we suggest that the karyotype of R. colombiensis and R. ecuadoriensis lost its heteropycnotic and heterochromatic blocks during speciation. Furthermore, this loss could be related to adaptation to different environments.

Distribution of constitutive heterochromatin and nucleolar organizer regions in two species of family Gomphidae (Odonata: Anisoptera)

Spermatogonial and primary spermatocyte chromosomes of Paragomphus lineatus (Selys) and Nepogomphus modestus (Selys) of family Gomphidae have been described on the basis of C-banding and NOR staining. Both the species possess 2n (♂) =23, n (♂) =12 without m chromosomes with XO(♂)/XX(♀) type sex determining mechanism. The sex chromosome is the largest element in the whole complement in Paragomphus lineatus but it is medium sized in Nepogomphus modestus. In Paragomphus lineatus, all the autosomal bivalents possess terminal C-bands while X chromosome is C-positive throughout the length but lightly stained in the centre. Similarly, terminal NOR bands are present on all the autosomal bivalents and X chromosome shows terminal NOR bands with large interstitial band. In Nepogomphus modestus, all the autosomal bivalents except one bivalent possess terminal C-bands while X chromosome represents large C-positive region on one end and small C-negative region on the other end. NOR staining shows terminal / non terminal NOR bands on some autosomal bivalents while X chromosome possesses dark NOR band only on one end.