Distribution Of C-heterochromatin Research Articles

Molecular and cytogenetic evidence for sibling species in the Chagas disease vector Triatoma maculata.

Triatoma maculata (Hemiptera, Reduviidae, Triatominae) occurs across dry-to-semiarid ecoregions of northern South America, where it transmits Trypanosoma cruzi, causative agent of Chagas disease. Using 207 field-caught specimens from throughout the species' range, mitochondrial(mt) DNA sequence data, and cytogenetics, we investigated inter-population genetic diversity and the phylogenetic affinities of T. maculata. Mitochondrial DNA sequence analyses (cytb and nd4) disclosed a monophyletic T. maculata clade encompassing three distinct geographic groups: Roraima formation (Guiana shield), Orinoco basin, and Magdalena basin (trans-Andean). Between-group cytb distances (11.0-12.8%) were larger than the ~7.5% expected for sister Triatoma species; the most recent common ancestor of these T. maculata groups may date back to the late Miocene. C-heterochromatin distribution and the sex-chromosome location of 45S ribosomal DNA clusters both distinguished Roraima bugs from Orinoco and Magdalena specimens. Cytb genealogies reinforced that T. maculata is not sister to Triatoma pseudomaculata and probably represents an early (middle-late Miocene) offshoot of the 'South American Triatomini lineage'. In sum, we report extensive genetic diversity and deep phylogeographic structuring in T. maculata, suggesting that it may consist of a complex of at least three sibling taxa. These findings have implications for the systematics, population biology, and perhaps medical relevance of T. maculata sensu lato.

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.

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

The extensive amplification of heterochromatin in Melipona bees revealed by high throughput genomic and chromosomal analysis.

Satellite DNAs (satDNAs) and transposable elements (TEs) are among the main components of constitutive heterochromatin (c-heterochromatin) and are related to their functionality, dynamics, and evolution. A peculiar case regarding the quantity and distribution of c-heterochromatin is observed in the genus of bees, Melipona, with species having a low amount of heterochromatin and species with high amount occupying almost all chromosomes. By combining low-pass genome sequencing and chromosomal analysis, we characterized the satDNAs and TEs of Melipona quadrifasciata (low c-heterochromatin) and Melipona scutellaris (high low c-heterochromatin) to understand c-heterochromatin composition and evolution. We identified 15 satDNA families and 20 TEs for both species. Significant variations in the repeat landscapes were observed between the species. In M. quadrifasciata, the repetitive fraction corresponded to only 3.78% of the genome library studied, whereas in M. scutellaris, it represented 54.95%. Massive quantitative and qualitative changes contributed to the differential amplification of c-heterochromatin, mainly due to the amplification of exclusive repetitions in M. scutellaris, as the satDNA MscuSat01-195 and the TE LTR/Gypsy_1 that represent 38.20 and 14.4% of its genome, respectively. The amplification of these two repeats is evident at the chromosomal level, with observation of their occurrence on most c-heterochromatin. Moreover, we detected repeats shared between species, revealing that they experienced mainly quantitative variations and varied in the organization on chromosomes and evolutionary patterns. Together, our data allow the discussion of patterns of evolution of repetitive DNAs and c-heterochromatin that occurred in a short period of time, after separation of the Michmelia and Melipona subgenera.

Systematic relationships within the Microtus arvalis (Rodentia: Cricetidae) group in Iran, inferred from cytogenetic analyses

The distribution of C-heterochromatin and nucleolar organizer regions (NORs) was studied in three species of voles of the Microtus arvalis group in Iran: M. mystacinus, M. kermanensis, and M. transcaspicus. The C-banding pattern and NORs distribution were similar in M. mystacinus and M. kermanensis suggesting taxonomic proximity of these two species. At the same time, the karyotypes of M. mystacinus from Iran were different in C-banding pattern from the complements of conspecific 54-chromosome voles from Europe and other regions of Asia. The most distinct difference was in size of the distal C-positive block of heterochromatin on the X chromosome. In this respect M. mystacinus from Iran and M. kermanensis resembled M. transcaspicus. Small size of the distal C-positive heterochromatic block may be ancestral whereas larger size is derived. The X chromosome of M. transcaspicus can be derived from that of M. mystacinus and M. kermanensis by a large inversion or centromeric shift.

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.

Cryptic speciation in the Triatoma sordida subcomplex (Hemiptera, Reduviidae) revealed by chromosomal markers.

BackgroundChagas disease vectors (Hemiptera-Reduviidae) comprise more than 140 blood-sucking insect species of the Triatominae subfamily. The largest genus is Triatoma, subdivided in several complexes and subcomplexes according to morphology, ecology and genetic features. One of them is the sordida subcomplex, involving four species: Triatoma sordida, T. guasayana, T. garciabesi and T. patagonica. Given the great morphological similarity of these species, their taxonomic identification, evolutionary relationships and population differentiation have been controversial for many years and even today remain under discussion.MethodsWe simultaneously analyzed two chromosomal markers, C-heterochromatin distribution and 45S ribosomal genes chromosomal position, of 139 specimens from several sordida subcomplex populations from Argentina, Bolivia, Brazil and Paraguay, collected both in nature and from several established insectaries. Our results were compared with COI sequences deposited in GenBank.ResultsWe recognized five chromosomal taxa with putative hybrids, which each differ in at least one chromosome marker. Most of them present significant differences in their mtDNA sequences.ConclusionThe chromosomal taxa here show a significant chromosome differentiation involving changes in the C-heterochromatin content and in the ribosomal clusters position. This paper identifies several erroneously classified populations by morphological methods, delimits the geographical distribution of each taxon and proposes the existence of a new cryptic species, widely distributed in Argentina. We also suggest that sordida sibling species involve closely related as well as evolutionary distant species. Taxonomic status of each chromosomal taxon is discussed considering phenotypic and genetic results previously published.

A cytological study of four SicilianSerapias(Orchidaceae)

Cytological analysis of four Serapias L. (Orchidaceae), of which two are Sicilian endemics, is carried out. In particular, the endemic S. intermedia subsp. hyblaea shows a triploid chromosome complement with 2n = 3x = 54, representing natural nothotaxa arising from a hybridization process between supposed parental S. vomeracea (2n = 2x = 36) and Serapias lingua (2n = 4x = 72). For each of them the C-heterochromatin distribution, using Giemsa C-banding and karyotypes, was examined. The other endemic taxon (S. orientalis subsp. siciliensis) is characterized by a diploid chromosome number 2n = 2x = 36, of which the C-heterochromatin distribution is examined as well. The taxonomical relationships among these taxa are discussed in relation to the literature data.

Chromosomal variation in social voles: a Robertsonian fusion in Günther’s vole

The study reports on chromosomes in several populations of social voles from south-eastern Europe and the Middle East. The standard karyotypes of individuals of Microtus hartingi and Microtus guentheri originating from both south-eastern Europe and Asia Minor comprised 54 mostly acrocentric chromosomes. However, variation between populations was found in the amount and distribution of C-heterochromatin in certain autosomes and the sex chromosomes. Furthermore, a specific pattern of argyrophilic nucleolar organizer region distribution was recorded in different geographic populations. In a population from Asia Minor, a heterozygous centric fusion of two autosomes was found. The G-banded karyotypes of M. guentheri and Microtus socialis were compared, and tandem fusions of autosomes were suggested as possible mechanism of the divergence. The karyotypes of the nine currently recognized species of social voles are reviewed, and implications of chromosomal data for systematics are evaluated.

C-banding and Ag-NOR distribution patterns in Euphrates jerboa, Allactaga euphratica (Mammalia: Rodentia), from Turkey

A chromosomal study of Allactaga euphratica from the Şanlıurfa Province in Southeast Anatolia, Turkey, was performed. The diploid number of 48 chromosomes was found in all four specimens examined. The C-band-positive regions were distributed in centromeric areas of all the autosomal pairs and the X chromosome. Extensive C-positive heterochromatin intercalary blocks were observed in the largest pair of autosomes. The small Y chromosome was stained uniformly and C-negatively. The active nucleolus organizer regions (NORs) were localized in two pairs of small bi-armed autosomes. The C-heterochromatin distribution and localization of the secondary constrictions bearing NORs apparently differ between karyotypes of the related jerboa species A. euphratica and Allactaga williamsi. This cytogenetic difference may be implied as a suitable marker in further studies of the relationships in contact zones and possible hybridization between these two taxa.

Meiotic karyotypes and testis structure of 14 species of the planthopper tribe Issini (Hemiptera: Fulgoroidea, Issidae)

Karyotypes and testis structure of 14 species representing 9 genera (Latissus, Bubastia, Falcidius, Kervillea, Mulsantereum, Mycterodus, Scorlupaster, Scorlupella and Zopherisca) of the planthopper tribe Issini (Issidae) are presented. All the karyotypes are illustrated by meiotic and occasionally mitotic figures. The male karyotypes of most of the species analyzed are 2n = 26 + X, the exception being Falcidius limbatus, which has a karyotype of 2n = 24 + neo-XY. The latter is the first report of the neo-XY system in the family Issidae. The species studied are found to be similar in having NORs on the largest pair of autosomes, but differ significantly in the amount and distribution of C-heterochromatin along the chromosomes. In contrast to the conserved chromosome numbers, the highly variable follicle number in the testes suggests rapid evolution of the tribe Issini. On the basis of its specific follicle number, it is proposed that Zopherisca tendinosa skaloula Gnezdilov & Drosopoulos, 2006 be upgrade to a species: Z. skaloula stat. n. The cytological and taxonomic significance of results presented are discussed.

Banded karyotypes of a belukha whale, Delphinapterus leucas.

Chromosomes of a belukha whale, Delphinapterus leucas (Monodontidae), were studied by homogeneous staining, G- and C-sequential banding, direct C-banding and N-banding. The belukha has a typical cetacean 2n=44 karyotype. Banded karyotypes were compared with previously published karyotypes of Monodon monoceros and delphinid cetaceans. All chromosomes were matched with homologues in Stenella, and differences were observed in the distribution of C-heterochromatin.

C-heterochromatin variation in the karyotype reflects species level distinction between Erinaceus roumanicus and E. concolor (Eulipotyphla: Erinaceidae) in Turkey

The distributions of C-heterochromatin blocks and nucleolar organizer regions (NORs) were studied in hedgehogs from the European (Thrace) and the Asiatic (Anatolia) parts of Turkey. Karyotypes with 48 chromosomes were found in all the specimens examined. The distribution of large heterochromatic blocks in autosomes was different between samples from Thrace and Anatolia in respect of the presence of a distal block in the autosome no. 15. These two chromosomal types correspond to the karyotypes designated as E II and E I by Mandahl (1978). The comparison with other published data shows that the karyotype E II is found within the range of Erinaceus roumanicus, whereas the karyotype EI occurs within the range of E. concolor. Both the species thus differ consistently in the distribution of C-heterochromatin blocks in their karyotypes. The NORs were found in five autosomal pairs of E. roumanicus, and in four autosomal pairs of E. concolor. The position of NORs in individual autosomal pairs may be variable, and two distinct variants were observed in the samples from northern and central/southern Anatolia, respectively. This variation may reflect the presence of two lineages within E. concolor that were indicated in previous phylogeographic studies.

First Evidence of Sex Chromosome Pre-reduction in Male Meiosis in the Miridae Bugs (Heteroptera)

The karyotype and male meiosis of Macrolophus costalis Fieber (Insecta, Heteroptera, Miridae) were studied using C-banding, AgNOR-banding and DNA sequence specific fluorochrome staining. The chromosome formula of the species is 2n = 28(24+X1X2X3Y). Male meiotic prophase is characterized by a prominent condensation stage. At this stage, two sex chromosomes, "X" and Y are positively heteropycnotic and always appeared together, while in autosomal bivalents homologous chromosomes were aligned side by side along their entire length, that is, meiosis is achiasmatic. At metaphase I, "X" and Y form a pseudobivalent and orient to the opposite poles. At early anaphase I, the "X" chromosome disintegrates into three separate small chromosomes, X1, X2, and X3. Hence both the autosomes and sex chromosomes segregate reductionally in the first anaphase, and separate equationally in the second anaphase. This is the first evidence of sex chromosome pre-reduction in the family Miridae. Data on C-heterochromatin distribution and its composition in the chromosomes of this species are discussed.

Holocentric chromosomes of psocids (Insecta, Psocoptera) analysed by C-banding, silver impregnation and sequence specific fluorochromes CMA3 and DAPI

The pattern of nucleolus attachment and C-heterochromatin distribution and molecular composition in the karyotypes of psocid species Psococerastis gibbosa (2n = 16+X), Blaste conspurcata (2n = 16+X) and Amphipsocus japonicus (2n = 14+neo-XY) were studied by C-banding, silver impregnation and sequence specific fluorochromes CMA3 and DAPI. Every species was found to have a single nucleolus in male meiosis. In P. gibbosa the nucleolus is attached to an autosomal bivalent; in B. conspurcata to the X-chromosome; in A. japonicus to the neo-XY bivalent. The species show a rather small amount of constitutive heterochromatin, C-blocks demonstrating telomeric localization with rare exceptions. P. gibbosa is characterized by a polymorphism for C-blocks occurrence and distribution. In the autosomes of this species, C-heterochromatin consists of AT-rich DNA except for the nucleolus organizing region, which is also GC-rich; the X-chromosome shows both AT- and GC-rich clusters. In A. japonicus and B. conspurcata, C-heterochromatin of the autosomes and sex chromosomes consists of both GC-rich and AT-rich DNA clusters, which are largely co-localized.

Evaluation of phylogenetic relationships between five polyploid Aegilops L. species of the U-genome cluster by means of chromosomal analysis

Four tetraploid (Aegilops ovata, Ae. biuncialis, Ae. columnaris, and Ae. triaristata) and one hexaploid (Ae. recta) species of the U-genome cluster were studied using C-banding technique. All species displayed broad C-banding polymorphism and high frequency of chromosomal rearrangements. Chromosomal rearrangements were represented by paracentric inversions and intragenomic and intergenomic translocations. We found that the processes of intraspecific divergence of Ae. ovata, Ae. biuncialis, and Ae. columnaris were probably associated with introgression of genetic material from other species. The results obtained confirmed that tetraploid species Ae. ovata and Ae. biuncialis occurred as a result of hybridization of a diploid Ae. umbellulata with Ae. comosa and Ae. heldreichii, respectively. The dissimilarity of the C-banding patterns of several chromosomes of these tetraploid species and their ancestral diploid forms indicated that chromosomal aberrations might have taken place during their speciation. Significant differences of karyotype structure, total amount and distribution of C-heterochromatin found between Ae. columnaris and Ae. triaristata, on the one hand, and Ae. ovata and Ae. biuncialis, on the other, evidenced in favor of different origin of these groups of species. In turn, similarity of the C-banding patterns of Ae. columnaris and Ae. triaristata chromosomes suggested that they were derived from a common ancestor. A diploid species Ae. umbellulata was the U-genome donor of Ae. columnaris and Ae. triaristata; however, the donor of the second genome of these species was not determined. We assumed that these tetraploid species occurred as a result of introgressive hybridization. Similarity of the C-banding patterns of chromosomes of Ae. recta and its parental species Ae. triaristata and Ae. uniaristata indicated that the formation of the hexaploid form was not associated with large modifications of the parental genomes.

Karyotypes of Two Indian Grasshoppers of Mecopodinae(Orthoptera-Tettigoniidae).

(1) The chromosomes of two species of the genus Mecopoda are described.(2) Mecopoda elongata has 2n=29 with 8 pairs of metacentric, 5 pairs of subacrocentric and one pair of acrocentric chromosomes. The karyotype of Mecopoda sp, consists of 2n=27 with all biarmed chromosomes- 8 pairs of metacentric, one pair of heteromorphic submetacentric with a secondary constriction in one homologue and 4 pairs of subacrocentric chromosomes. In both, the X chromosome is large and metacentric.(3) The basic karyotype of the genus Mecopoda is assumed to be 2n=31 with all acrocentric chromosomes and the karyotypes of M. elongata and Mecopoda sp. are considered to be derived from such a basic karyotype by the mechanisms of centric fusion and pericentric inverson.(4) The C-banded karyotype of Mecopoda sp. is presented showing the characteristic distribution of C-heterochromatin.

Giemsa C-banding pattern in some cultivars of Trichosanthes dioica Roxb.

To assess the role of heterochromatin, if any, in intraspecific diversification, a detailed study of the distribution pattern of Giemsa C-heterochromatin in three gynoecious cultivars of Trichosanthes dioica Roxb., namely, ‘Kali, ‘Kalyani’ and ‘Sanjiban’ has been undertaken.The somatic chromosomes are characterized by distinct telomeric bands. The differential banding pattern can be conveniently used for distinguishing between the cultivars. The cultivar ‘Sanjiban’ stands apart from the rest in possessing seven chromosomes with one or more intercalary bands in addition to the telomeric bands at both arms. The cultivars ‘Kali’ and ‘Kalyani’, however, can be distinguished from each other by the presence of five chromosomes with two telomeric bands in each in the former while four such chromosomes are represented in the latter.The application of Giemsa C-banding method reveals a differential distribution of C-heterochromatin in the cultivars investigated thus demonstrating the active involvement of heterochromatin in intraspecific diversification of T. dioica.

Chromosome Location of Active Ribosomal Genes inPleurodema Thaul(Amphibia-Leptodactylidae). C-Banding and Polymorphism of The Nucleolar Organizer Region

SUMMARYSpecimens of Pleurodema thaul collected in three localities from central Chile (32–33 SL), were studied. Patterns of C-heterochromatin distribution, localization and activity of Nucleolar Organizer Regions (NORs) were established using the silver banding technique and the fluorochrome quinacrine mustard. It was show that specimens from all localities have the same pattern of C-bands. In all except three specimens from one population there are only two NORs on chromosome pair number 8 in correspondence with two secondary constrictions present in Giemsa or quinacrine mustard stained chromosomes. In this three specimens, there is a supplementary secondary constriction in pair number 3, where there are active DNAr genes as is revealed by the silver chromosome stain and the number of nucleoli found in the interphase nuclei. Most specimens have differences in NORs length when carrier chromosomes are compared. However, there are no differences in nucleolar sizes in their interphase nuclei. The significance of NOR polymorphism and differences in length of this genome region are discussed.

Chromosome analysis of Dalton's lymphoma adapted to the Swiss mouse: Clonal evaluation and C-heterochromatin distribution

Chromosome studies of Dalton's lymphoma, which was originally developed in the DBA/2 mouse and later adapted to a close inbred strain of the Swiss albino mouse, revealed only one rb-marker in all cells bearing a modal number (71). After several successive in vivo passages of the tumor, a new cell clone appeared with a different modal number (70) and two rb-markers. This new cell clone gradually outnumbered the stem cells and an apparent enhancement in tumorigenicity was noted. C-banding of the new cell clone revealed that one of the two telomeric heterochromatin-bearing chromosomes, originally present in the stem cells, had been involved in a Robertsonian fusion to form the additional marker chromosome. G-banded analysis indicated the noninvolvement of chromosome #15 in the fusion.