Chromosome banding in Amphibia. VIII. An unusual XY/XX-sex chromosome system in Gastrotheca riobambae (Anura, Hylidae)

Comparative Distribution of Repetitive Sequences in the Karyotypes of Xenopus tropicalis and Xenopus laevis (Anura, Pipidae)

Xenopus laevis and its diploid relative, Xenopus tropicalis, are the most used amphibian models. Their genomes have been sequenced, and they are emerging as model organisms for research into disease mechanisms. Despite the growing knowledge on their genomes based on data obtained from massive genome sequencing, basic research on repetitive sequences in these species is lacking. This study conducted a comparative analysis of repetitive sequences in X. laevis and X. tropicalis. Genomic in situ hybridization (GISH) and fluorescence in situ hybridization (FISH) with Cot DNA of both species revealed a conserved enrichment of repetitive sequences at the ends of the chromosomes in these Xenopus species. The repeated sequences located on the short arm of chromosome 3 from X. tropicalis were not related to the sequences on the short arm of chromosomes 3L and 3S from X. laevis, although these chromosomes were homoeologous, indicating that these regions evolved independently in these species. Furthermore, all the other repetitive sequences in X. tropicalis and X. laevis may be species-specific, as they were not revealed in cross-species hybridizations. Painting experiments in X. laevis with chromosome 7 from X. tropicalis revealed shared sequences with the short arm of chromosome 3L. These regions could be related by the presence of the nucleolus organizer region (NOR) in both chromosomes, although the region revealed by chromosome painting in the short arm of chromosome 3L in X. laevis did not correspond to 18S + 28S rDNA sequences, as they did not colocalize. The identification of these repeated sequences is of interest as they provide an explanation to some problems already described in the genome assemblies of these species. Furthermore, the distribution of repetitive DNA in the genomes of X. laevis and X. tropicalis might be a valuable marker to assist us in understanding the genome evolution in a group characterized by numerous polyploidization events coupled with hybridizations.

Sex chromosome evolution in frogs-helpful insights from chromosome painting in the genus Engystomops

The differentiation of sex chromosomes is thought to be interrupted by relatively frequent sex chromosome turnover and/or occasional recombination between sex chromosomes (fountain-of-youth model) in some vertebrate groups as fishes, amphibians, and lizards. As a result, we observe the prevalence of homomorphic sex chromosomes in these groups. Here, we provide evidence for the loss of sex chromosome heteromorphism in the Amazonian frogs of the genus Engystomops, which harbors an intriguing history of sex chromosome evolution. In this species complex composed of two named species, two confirmed unnamed species, and up to three unconfirmed species, highly divergent karyotypes are present, and heteromorphic X and Y chromosomes were previously found in two species. We describe the karyotype of a lineage estimated to be the sister of all remaining Amazonian Engystomops (named Engystomops sp.) and perform chromosome painting techniques using one probe for the Y chromosome and one probe for the non-centromeric heterochromatic bands of the X chromosome of E. freibergi to compare three Engystomops karyotypes. The Y probe detected the Y chromosomes of E. freibergi and E. petersi and one homolog of chromosome pair 11 of Engystomops sp., suggesting their common evolutionary origin. The X probe showed no interspecific hybridization, revealing that X chromosome heterochromatin is strongly divergent among the studied species. In the light of the phylogenetic relationships, our data suggest that sex chromosome heteromorphism may have occurred early in the evolution of the Amazonian Engystomops and have been lost in two unnamed but confirmed candidate species.

Evolution of Bird Sex Chromosomes Narrated by Repetitive Sequences: Unusual W Chromosome Enlargement in Gallinula melanops (Aves: Gruiformes: Rallidae)

Among birds, species with the ZZ/ZW sex determination system generally show significant differences in morphology and size between the Z and W chromosomes (with the W usually being smaller than the Z). In the present study, we report for the first time the karyotype of the spot-flanked gallinule (Gallinula melanops) by means of classical and molecular cytogenetics. The spot-flanked gallinule has 2n = 80 (11 pairs of macrochromosomes and 29 pairs of microchromosomes) with an unusual W chromosome that is larger than the Z. Besides being totally heterochromatic, it has a secondary constriction in its long arm corresponding to the nucleolar organizer region, as confirmed by both silver staining and mapping of 18S rDNA probes. This is an unprecedented fact among birds. Additionally, 18S rDNA sites were also observed in 6 microchromosomes, while 5S rDNA was found in just 1 microchromosomal pair. Seven out of the 11 used microsatellite sequences were found to be accumulated in microchromosomes, and 6 microsatellite sequences were found in the W chromosome. In addition to the involvement of heterochromatin and repetitive DNAs in the differentiation of the large W chromosome, the results also show an alternative scenario that highlights the plasticity that shapes the evolutionary history of bird sex chromosomes.

Highly conserved Z and molecularly diverged W chromosomes in the fish genus Triportheus (Characiformes, Triportheidae)

The main objectives of this study were to test: (1) whether the W-chromosome differentiation matches to species' evolutionary divergence (phylogenetic concordance) and (2) whether sex chromosomes share a common ancestor within a congeneric group. The monophyletic genus Triportheus (Characiformes, Triportheidae) was the model group for this study. All species in this genus so far analyzed have ZW sex chromosome system, where the Z is always the largest chromosome of the karyotype, whereas the W chromosome is highly variable ranging from almost homomorphic to highly heteromorphic. We applied conventional and molecular cytogenetic approaches including C-banding, ribosomal DNA mapping, comparative genomic hybridization (CGH) and cross-species whole chromosome painting (WCP) to test our questions. We developed Z- and W-chromosome paints from T. auritus for cross-species WCP and performed CGH in a representative species (T. signatus) to decipher level of homologies and rates of differentiation of W chromosomes. Our study revealed that the ZW sex chromosome system had a common origin, showing highly conserved Z chromosomes and remarkably divergent W chromosomes. Notably, the W chromosomes have evolved to different shapes and sequence contents within ~15-25 Myr of divergence time. Such differentiation highlights a dynamic process of W-chromosome evolution within congeneric species of Triportheus.

Cytogenetic Insights into the Evolution of Chromosomes and Sex Determination Reveal Striking Homology of Turtle Sex Chromosomes to Amphibian Autosomes

Turtle karyotypes are highly conserved compared to other vertebrates; yet, variation in diploid number (2n = 26-68) reflects profound genomic reorganization, which correlates with evolutionary turnovers in sex determination. We evaluate the published literature and newly collected comparative cytogenetic data (G- and C-banding, 18S-NOR, and telomere-FISH mapping) from 13 species spanning 2n = 28-68 to revisit turtle genome evolution and sex determination. Interstitial telomeric sites were detected in multiple lineages that underwent diploid number and sex determination turnovers, suggesting chromosomal rearrangements. C-banding revealed potential interspecific variation in centromere composition and interstitial heterochromatin at secondary constrictions. 18S-NORs were detected in secondary constrictions in a single chromosomal pair per species, refuting previous reports of multiple NORs in turtles. 18S-NORs are linked to ZW chromosomes in Apalone and Pelodiscus and to X (not Y) in Staurotypus. Notably, comparative genomics across amniotes revealed that the sex chromosomes of several turtles, as well as mammals and some lizards, are homologous to components of Xenopus tropicalis XTR1 (carrying Dmrt1). Other turtle sex chromosomes are homologous to XTR4 (carrying Wt1). Interestingly, all known turtle sex chromosomes, except in Trionychidae, evolved via inversions around Dmrt1 or Wt1. Thus, XTR1 appears to represent an amniote proto-sex chromosome (perhaps linked ancestrally to XTR4) that gave rise to turtle and other amniote sex chromosomes.

Unraveling the Sex Chromosome Heteromorphism of the Paradoxical Frog Pseudis tocantins

The paradoxical frog Pseudis tocantins is the only species in the Hylidae family with known heteromorphic Z and W sex chromosomes. The Z chromosome is metacentric and presents an interstitial nucleolar organizer region (NOR) on the long arm that is adjacent to a pericentromeric heterochromatic band. In contrast, the submetacentric W chromosome carries a pericentromeric NOR on the long arm, which is adjacent to a clearly evident heterochromatic band that is larger than the band found on the Z chromosome and justify the size difference observed between these chromosomes. Here, we provide evidence that the non-centromeric heterochromatic bands in Zq and Wq differ not only in size and location but also in composition, based on comparative genomic hybridization (CGH) and an analysis of the anuran PcP190 satellite DNA. The finding of PcP190 sequences in P. tocantins extends the presence of this satellite DNA, which was previously detected among Leptodactylidae and Hylodidae, suggesting that this family of repetitive DNA is even older than it was formerly considered. Seven groups of PcP190 sequences were recognized in the genome of P. tocantins. PcP190 probes mapped to the heterochromatic band in Wq, and a Southern blot analysis indicated the accumulation of PcP190 in the female genome of P. tocantins, which suggests the involvement of this satellite DNA in the evolution of the sex chromosomes of this species.

Cytogenetic analysis of Scinaxauratus and Scinaxeurydice (Anura, Hylidae) with emphasis on cytotaxonomy

Scinax Wagler, 1830 is a species-rich genus of amphibians with relatively few detailed chromosomal reports. In this work, cytogenetic analyses of Scinaxauratus (Wied-Neuwied, 1821) and Scinaxeurydice (Bokermann, 1968) were carried out based on conventional (Giemsa staining, Ag-NOR and C-banding) and cytomolecular (base-specific fluorochrome staining and fluorescence in situ hybridization - FISH of ribosomal probes) techniques. Both species shared the same karyotype, location of active nucleolar organizer regions on pair 11 and GC-rich heterochromatin, as reported for most species in Scinaxruber clade. Interpopulation chromosomal variation was observed in Scinaxeurydice, indicating the occurrence of cryptic species. The mapping of 18S ribosomal genes by FISH is reported for the first time in both species.

Chromosome landmarks and autosome-sex chromosome translocations in Rumex hastatulus, a plant with XX/XY1Y2 sex chromosome system

Rumex hastatulus is the North American endemic dioecious plant with heteromorphic sex chromosomes. It is differentiated into two chromosomal races: Texas (T) race characterised by a simple XX/XY sex chromosome system and North Carolina (NC) race with a polymorphic XX/XY1Y2 sex chromosome system. The gross karyotype morphology in NC race resembles the derived type, but chromosomal changes that occurred during its evolution are poorly understood. Our C-banding/DAPI and fluorescence in situ hybridization (FISH) experiments demonstrated that Y chromosomes of both races are enriched in DAPI-positive sequences and that the emergence of polymorphic sex chromosome system was accompanied by the break of ancestral Y chromosome and switch in the localization of 5S rDNA, from autosomes to sex chromosomes (X and Y2). Two contrasting domains were detected within North Carolina Y chromosomes: the older, highly heterochromatinised, inherited from the original Y chromosome and the younger, euchromatic, representing translocated autosomal material. The flow-cytometric DNA estimation showed ∼3.5 % genome downsizing in the North Carolina race. Our results are in contradiction to earlier reports on the lack of heterochromatin within Y chromosomes of this species and enable unambiguous identification of autosomes involved in the autosome-heterosome translocation, providing useful chromosome landmarks for further studies on the karyotype and sex chromosome differentiation in this species.

The sex chromosomes of frogs: variability and tolerance offer clues to genome evolution and function

Frog sex chromosomes offer an ideal system for advancing our understanding of genome evolution and function because of the variety of sex determination systems in the group, the diversity of sex chromosome maturation states, the ease of experimental manipulation during early development. After briefly reviewing sex chromosome biology generally, we focus on what is known about frog sex determination, sex chromosome evolution, and recent, genomics-facilitated advances in the field. In closing we highlight gaps in our current knowledge of frog sex chromosomes, and suggest priorities for future research that can advance broad knowledge of gene dose and sex chromosome evolution.

Karyological characterization of the endemic Iberian rock lizard, Iberolacerta monticola (Squamata, Lacertidae): insights into sex chromosome evolution

Rock lizards of the genus Iberolacerta constitute a promising model to examine the process of sex chromosome evolution, as these closely related taxa exhibit remarkable diversity in the degree of sex chromosome differentiation with no clear phylogenetic segregation, ranging from cryptic to highly heteromorphic ZW chromosomes and even multiple chromosome systems (Z1Z1Z2Z2/Z1Z2W). To gain a deeper insight into the patterns of karyotype and sex chromosome evolution, we performed a cytogenetic analysis based on conventional staining, banding techniques and fluorescence in situ hybridization in the species I. monticola, for which previous cytogenetic investigations did not detect differentiated sex chromosomes. The karyotype is composed of 2n = 36 acrocentric chromosomes. NORs and the major ribosomal genes were located in the subtelomeric region of chromosome pair 6. Hybridization signals of the telomeric sequences (TTAGGG)n were visualized at the telomeres of all chromosomes and interstitially in 5 chromosome pairs. C-banding showed constitutive heterochromatin at the centromeres of all chromosomes, as well as clear pericentromeric and light telomeric C-bands in several chromosome pairs. These results highlight some chromosomal markers which can be useful to identify species-specific diagnostic characters, although they may not accurately reflect the phylogenetic relationships among the taxa. In addition, C-banding revealed the presence of a heteromorphic ZW sex chromosome pair, where W is smaller than Z and almost completely heterochromatic. This finding sheds light on sex chromosome evolution in the genus Iberolacerta and suggests that further comparative cytogenetic analyses are needed to understand the processes underlying the origin, differentiation and plasticity of sex chromosome systems in lacertid lizards.

Karyotypic differentiation via 2n reduction and a finding of a case of triploidy in anurans of the genus Engystomops (Anura, Leiuperidae)

The genus Engystomops is divided into two groups, namely the Duovox clade and the Edentulus clade. The species of Edentulus clade have karyotypes with 2n = 22, while E. pustulatus and E. puyango, which belong to Duovox clade, have 2n = 20. To investigate if 2n = 20 is a synapomorphy of Duovox clade, we cytogenetically analyzed all the species of this group, except for E. puyango, in the present study. All of them had 2n = 20, differing from the species of Edentulus clade. Since the species already karyotyped of the genus Physalaemus, which is considered to be the sister group of Engystomops, also have 2n = 22, we conclude that the 2n reduction is a synapomorphy of Duovox clade. Despite the karyotypes of all the species of Duovox clade were very similar, they varied in the NOR pattern. In E. coloradorum, an additional NOR was found in one homologue of the chromosome pair 10 exclusively in all females, indicating that this could possibly be a sexual pair of the ZZ/ZW system. Also in this species, it was found the first case of natural polyploidy of the genus Engystomops.

High tandem repeat content in the genome of the short-lived annual fish Nothobranchius furzeri: a new vertebrate model for aging research

BACKGROUND

The annual fish Nothobranchius furzeri is the vertebrate with the shortest known life span in captivity. Fish of the GRZ strain live only three to four months under optimal laboratory conditions, show explosive growth, early sexual maturation and age-dependent physiological and behavioral decline, and express aging related biomarkers. Treatment with resveratrol and low temperature significantly extends the maximum life span. These features make N. furzeri a promising new vertebrate model for age research.

RESULTS

To contribute to establishing N. furzeri as a new model organism, we provide a first insight into its genome and a comparison to medaka, stickleback, tetraodon and zebrafish. The N. furzeri genome contains 19 chromosomes (2n = 38). Its genome of between 1.6 and 1.9 Gb is the largest among the analyzed fish species and has, at 45%, the highest repeat content. Remarkably, tandem repeats comprise 21%, which is 4-12 times more than in the other four fish species. In addition, G+C-rich tandem repeats preferentially localize to centromeric regions. Phylogenetic analysis based on coding sequences identifies medaka as the closest relative. Genotyping of an initial set of 27 markers and multi-locus fingerprinting of one microsatellite provides the first molecular evidence that the GRZ strain is highly inbred.

CONCLUSIONS

Our work presents a first basis for systematic genomic and genetic analyses aimed at understanding the mechanisms of life span determination in N. furzeri.

Different origins of bird and reptile sex chromosomes inferred from comparative mapping of chicken Z-linked genes

Recent progress of chicken genome projects has revealed that bird ZW and mammalian XY sex chromosomes were derived from different autosomal pairs of the common ancestor; however, the evolutionary relationship between bird and reptilian sex chromosomes is still unclear. The Chinese soft-shelled turtle (Pelodiscus sinensis) exhibits genetic sex determination, but no distinguishable (heteromorphic) sex chromosomes have been identified. In order to investigate this further, we performed molecular cytogenetic analyses of this species, and thereby identified ZZ/ZW-type micro-sex chromosomes. In addition, we cloned reptile homologues of chicken Z-linked genes from three reptilian species, the Chinese soft-shelled turtle and the Japanese four-striped rat snake (Elaphe quadrivirgata), which have heteromorphic sex chromosomes, and the Siam crocodile (Crocodylus siamensis), which exhibits temperature-dependent sex determination and lacks sex chromosomes. We then mapped them to chromosomes of each species using FISH. The linkage of the genes has been highly conserved in all species: the chicken Z chromosome corresponded to the turtle chromosome 6q, snake chromosome 2p and crocodile chromosome 3. The order of the genes was identical among the three species. The absence of homology between the bird Z chromosome and the snake and turtle Z sex chromosomes suggests that the origin of the sex chromosomes and the causative genes of sex determination are different between birds and reptiles.

Cytogenetics of the bleak (Alburnus alburnus), with special emphasis on the B chromosomes

Some of the largest B chromosomes so far discovered in vertebrates are present in the cyprinid fish Alburnus alburnus. Previous cytogenetic analyses revealed a diploid chromosome number of 2n = 50. In addition, in some individuals one or two unusually large B chromosomes are present. Two morphologically different types of B chromosomes were observed. The frequency of animals bearing a supernumerary chromosome was found to vary considerably between different populations. A more detailed analysis of the A and B chromosomes of A. alburnus by conventional banding techniques, as well as fluorescence in-situ hybridization (FISH) with the telomeric DNA repeats (GGGTTA)7/(TAACCC)7, 18S + 28S rDNA and 5S rDNA were performed in the present study. Furthermore, a B chromosome-specific DNA probe obtained by amplified length polymorphism (AFLP) was hybridized on metaphases of A. alburnus carrying supernumerary B chromosomes. The banding analyses showed that the B chromosomes are completely heterochromatic, consist of GC-rich DNA sequences, replicate their DNA in the very late S-phase of the cell cycle and are composed mainly of a specific retrotransposable DNA element. Finally, blood probes from A. alburnus were collected for DNA-flow cytometric measurements. It could be shown that the huge supernumerary chromosomes represent nearly 10% of the total genome size of A. alburnus.

Heterochromatin of the scarab beetle, Bubas bison (Coleoptera: Scarabaeidae) II. Evidence for AT-rich compartmentalization and a high amount of rDNA copies

An unexpected result arising from a previous characterization of the scarab beetle Bubas bison (Coleoptera: Scarabaeidae) heterochromatin was its unusual homogeneous reaction to different staining methods. In particular, silver stainability of heterochromatic ends of all chromosomes prevented identification of the number of rDNA transcriptionally active regions. Data formerly obtained using silver impregnation (Ag-NOR), C- G- and DAPI banding are here improved and completed by application of CMA(3) staining and rDNA FISH with the aim to investigate heterochromatin base composition and locate rDNA regions with respect to NOR-associated heterochromatin. Our results show that B. bison has a high amount of heterochromatin (almost 50%) and that--as revealed by rDNA FISH--major rRNA genes are spread over the heterochromatic telomeric regions of eight chromosomes, thus suggesting that only a portion, although consistent, of total heterochromatin is associated with ribosomal clusters. Moreover, DAPI-positive (AT-specific) and CMA(3)-negative (GC-specific) reactions of heterochromatic DNA confirm its AT-rich composition. Finally, possible explanations for the bright DAPI-fluorescence of both heterochromatin and rDNA sequences are discussed.

Multiple origins of tetraploid taxa in the Eurasian Bufo viridis subgroup

We used Q-banding and analyzed nucleolar organizing regions (NORs) to study the cytogenetic evolution of tetraploids within the Palearctic Bufo viridis subgroup, the only known amphibian complex comprising di-, tri- and tetraploid bisexually reproducing taxa. We examined three diploid (2n) nominal taxa (Bufo viridis viridis, B. v. turanensis, B. v. kermanensis) from five Eurasian localities and six tetraploid (4n) nominal taxa (B. oblongus, B. o. danatensis, B. pewzowi pewzowi, B. p. taxkorensis, B. p. unicolor, B. p. strauchi) from eight Central Asian localities. Homeologous chromosomes of 2n and 4n toads exhibit a similar morphology. Silver-staining and in situ hybridization revealed terminal NORs in the long arms of chromosomes 6 in all 2n but in only two out of four chromosomes 6 in all 4n taxa. Q-banding and a rapidly evolving mitochondrial marker suggest at least two origination events for Asian 4n toads: "Western Central Asian tetraploids" (B. oblongus Nikolsky, 1896) exhibit distinct differences within some chromosome quartets, which are divisible into pairs of chromosomes and may be allopolyploid. In contrast, "Central Asian tetraploids" (B. pewzowi Bedriaga, 1898) showed homogenous Q-banding patterns within each quartet, suggesting autopolyploidy. In Northeastern Iran, we discovered a zone of either common ancestry or hybridization of 2n and Western Central Asian 4n toads. This raises intriguing questions about how diploid and tetraploid taxa may evolve by exchanging genetic material.

Karyotype, banding and rDNA FISH in the scarab beetle Anoplotrupes stercorosus (Coleoptera Scarabaeoidea: Geotrupidae). Description and comparative analysis

Six specimens of Anoplotrupes stercorosus (Coleoptera Scarabaeoidea: Geotrupidae) were analysed using conventional staining, banding techniques and fluorescent in situ hybridization with a ribosomal probe (rDNA FISH). Detailed karyotype description was also joined to a comparative analysis between present data and those previously reported for Thorectes intermedius [Chromosome Res. 7 (1999) 1]. The two species, both belonging to the tribe Geotrupini, show the same modal number but different autosomal morphology which is in contrast with the high chromosome stability argued for Geotrupinae during the last three decades. Moreover, a detailed comparison reveals the occurrence of a plesiomorphic condition in A. stercorosus with respect to the apomorphic one of T. intermedius. This finding agrees with phylogenetic relationships proposed for the two genera based on morphological and anatomical characters.

Chromosome analysis using different staining techniques and fluorescent in situ hybridization in Cerithium vulgatum (Gastropoda: Cerithiidae)

In the present paper one population of the large" subtidal mollusc Cerithium vulgatum Bruguière, 1792 (Gastropoda: Cerithiidae) from the Northwestern coast of Sicily was investigated from a karyological point of view. The chromosome complement was Giemsa stained, conventionally karyotyped in 18 homomorphic chromosome pairs (10 bi-armed and 8 mono-armed), and subsequently analysed using silver, CMA3 and DAPI staining, and fluorescent in situ hybridization (FISH) with three repetitive DNA probes [ribosomal DNA (rDNA), (TTAGGG)n and (GATA)n]. FISH with the rDNA probe consistently mapped major ribosomal sites (18S-28S rDNA) in the terminal region of the short arms of one small sized mono-armed chromosome pair. Ribosomal DNA was transciptionally active as indicated by its preferential impregnation with silver nitrate (Ag-NOR) and did not contain a high amount of GC base pairs as suggested by the lack of a bright CMA3 fluorescence. The (TTAGGG)n telomeric probe was hybridized to the termini of nearly all chromosomes, thus demonstrating that, in C. tulgatum, this sequence has been conserved during the genomic evolution. The finding of the telomeric hexanucleotide in six species belonging to the three high taxa of Gastropoda supports the notion that this sequence is widespread within this class. The (GATA)n probe did not label any chromosome regions except for a minute terminal area of a single bivalent at pachytene stage.

Evidence for male XO sex-chromosome system in Pentodon bidens punctatum (Coleoptera Scarabaeoidea: Scarabaeidae) with X-linked 18S-28S rDNA clusters

In scarab beetle species of the genus Pentodon, the lack of analysis of sex chromosomes in females along with the poor characterization of sex chromosomes in the males, prevented all previous investigations from conclusively stating sex determination system. In this study, somatic chromosomes from females and spermatogonial chromosomes from males of Pentodon bidens punctatum (Coleoptera: Scarabaeoidea: Scarabaeidae) from Sicily have been analyzed using non-differential Giemsa staining. Two modal numbers of chromosomes were obtained: 2n = 20 and 19 in females and males, respectively. This finding along with other karyological characteristics such as the occurrence of one unpaired, heterotypic chromosome at metaphase-I and two types of metaphase-II spreads in spermatocytes demonstrate that a XO male/XX female sex determining mechanism - quite unusual among Scarabaeoidea - operates in the species investigated here. Spermatocyte chromosomes have also been examined after a number of banding techniques and fluorescent in situ hybridization with ribosomal sequences as a probe (rDNA FISH). The results obtained showed that silver and CMA(3) staining were inadequate to localize the chromosome sites of nucleolus organizer regions (NORs) due to the over-all stainability of both constitutive heterochromatin and heterochromatin associated to the NORs. This suggests that heterochromatic DNA of P. b. punctatum is peculiar as compared with other types of heterochromatin studied so far in other invertebrate taxa. By rDNA FISH major ribosomal genes were mapped on the X chromosome.

G and C banding show structural differences between the Z and W chromosomes in the frog Buergeria buergeri

G and C banding studies were made on cultured blood cells of matured male and female Buergeria (B.) buergeri frogs. The Z is subtelocentric and the W is submetacentric. There is a satellite near the end of the long arm of the Z. Constitutive heterochromatin is seen near the proximal and distal portions of the long arms of both Z and W. A single heavily stained G band is seen in the short arm of Z, while one or two heavily stained G bands are observed in the short arm of W. The Z may have originated through a process, in the course of which parts of W have been translocated to Z.

Cytogenetic and molecular studies in a lungfish, Protopterus annectens (Osteichthyes, Dipnoi)

A neontological approach to the problem of the origin of tetrapods consists in the examination of the available cytological and molecular data on the genome of these vertebrates. Dipnoans are a group of osteichthyian fishes, the evolutionary relationships of which with tetrapods have been disputed since their discovery. In the past, they were variously considered as being related to actinistians, tetrapods, and lower actinopterygians, though nowadays they are considered a monophyletic group, the sister group of crossopterygians. Dipnoans first appeared in the geologic record in the Early Devonian with 50 extinct genera, surviving up to date, with only three genera: Lepidosiren, Neoceratodus and Protopterus, including only six recognized species. Nothing is known of the genome of the early tetrapods, except that they and the Choanoichthyes exhibited a remarkable interspecific variability of the karyotype and of DNA content. These characteristics are often found in dipnoans and in the extant lissamphibians. Very little is known about the evolutionary karyology in the four Protopterus species and in the dipnoan clade in general. In this paper, we karyotyped ten male and female specimens of P. annectens (2n=34) from Nigeria. Moreover, we localized heterochromatin and nucleolar organizer regions by using base-specific fluorochromes and detected the human telomeric (TTAGGG)(n) sequences on all the telomeric sites of P. annectens chromosomes. DNA was also extracted and digested with seven restriction enzymes, which revealed the probable presence of almost three different families of satellite DNA. Nuclear DNA content was identified from blood samples by flow cytometry. New genomic and karyological data were compared and discussed with those on closer genera and taxa available in literature.

Evolutionary aspects of the ZZ/ZW sex chromosome system in the Characidae fish, genus Triportheus. A monophyletic state and NOR location on the W chromosome

Four species/populations of Triportheus, T. guentheri, T. cf. elongatus and T. paranense from different Brazilian hydrographic basins, were studied cytogenetically. All the species showed a similar karyotypic macrostructure, with a diploid chromosome number 2n = 52 and a ZZ/ZW sex chromosome system. Besides silver- and fluorochrome-staining, the chromosome mapping of 18S rDNA was also investigated using a biotinylated probe. In spite of some variation in the number of the NORs, a major chromosome site was always present on the short arm of an autosomal pair. In addition, a characteristic rDNA site was also observed on the telomeric region of the W chromosome in the four species/populations. In Triportheus differential reduction in size and heterochromatin accumulation appear to be the main processes associated with the evolution of the sex W chromosome. The location of rRNA genes on this chromosome may correspond to a plesiomorphic condition in the genus and, if so, predates to the sex chromosome system differentiation, with a possible influence in the initial steps of this process.

Organometallic complexes with biological molecules. XVII. Triorganotin(IV) complexes with amoxicillin and ampicillin

Novel triorganotin(IV) complexes of two beta-lactamic antibiotics, 6-[D-(-)-beta-amino-p-hydroxyphenyl-acetamido]penicillin (=amoxicillin) and 6-[D-(-)-alpha-aminobenzyl]penicillin (=ampicillin), have been synthesized and investigated both in solid and solution states. The complexes corresponded to the general formula R(3)Sn(IV)antib*H(2)O (R=Me, n-Bu, Ph; antib=amox=amoxicillinate or amp=ampicillinate). Structural investigations about configuration in the solid state have been carried out by interpreting experimental IR and 119Sn Mössbauer data. In particular, IR results suggested polymeric structures both for R(3)Sn(IV)amox.H(2)O and R(3)Sn(IV)amp*H(2)O. Moreover, both antibiotics appear to behave as monoanionic bidentate ligands coordinating the tin(IV) atom through ester-type carboxylate, as well as through the beta-lactamic carbonyl. Evidence that in none of these compounds water molecules were involved in coordination, was provided by thermogravimetric investigations. On the basis of 119Sn Mössbauer spectroscopy it can be inferred that tin(IV) was pentacoordinate in all of the complexes in the solid state, showing an equatorial R(3)Sn(IV) trigonal bipyramidal (tbp) configuration. The nature of the complexes in solution state was investigated by using 1H and 13C nuclear magnetic resonance (NMR) spectroscopy, while an 119Sn spectrum was obtained for n-Bu(3)Sn(IV)amp*H(2)O. Although 1H- and 13C-NMR measurements suggested that in dimethyl sulfoxide (DMSO)-d(6) solution the polymeric structure collapsed, due to a solvolysis process of the beta-lactamic carbonyl bonding to the organometallic moiety, the complexes have been shown to maintain the same trigonal bipyramidal configuration at tin(IV) atom by the coordination of a DMSO molecule. Cytotoxic activity of these novel semisynthetic antibiotic derivatives has been tested towards spermatocyte chromosomes of the mussel Brachidontes pharaonis (Mollusca: Bivalvia) using two different chromosome-staining techniques such as Giemsa and CMA(3). The occurrence of typical colchicinized-like (c-like) mitoses on slides obtained from animals exposed to organotin compounds, directly confirmed the high mitotic spindle-inhibiting potency of these chemicals. In addition, by comparative analysis of spermatocyte chromosomes from untreated specimens (negative controls) and specimens treated with the triorganotin(IV) complexes, structural damages such as 'achromatic lesions' and 'chromosome breakages' have been identified.

Chromosome analysis and rDNA FISH in the stag beetle Dorcus parallelipipedus L. (Coleoptera: Scarabaeoidea: Lucanidae)

In the present work the chromosome complement (2n = 18; 8AA + XY) of the stag beetle Dorcus parallelipipedus L. (Scarabaeoidea: Lucanidae) is analyzed using conventional Giemsa staining, banding techniques and ribosomal fluorescent in situ hybridization (rDNA FISH). rDNA FISH remains the unique tool for providing a clear-cut identification of Nucleolar Organizer Regions (NORs) when conventional banding methods such as silver- and CMA3-staining proved to be inadequate. The dull, homogeneous CMA3 fluorescence of all chromosomes indicates the absence of markedly GC rich compartmentalized regions in D. parallelipipedus genome. Silver impregnation inadequacy in detecting NOR regions is to be sought in the unusual extensive silver stainability of heterochromatic material which, on the contrary of what stated for vertebrates, seems to be a common feature in Scarabaeoidea species.

Cytogenetics of nine species of mediterranean blennies and additional evidence for an unusual multiple sex-chromosome system in Parablennius tentacularis (Perciformes, Blenniidae)

The chromosomal complements of nine species of Blenniidae (Aidablennius sphylnx, Blennius ocellaris, Lypophris adriaticus, L. pavo, L. trigloides, Parcablennius gattorugine, P. ponticus, P. sanguinolentus, P. tentacularis) from the Adriatic Sea were analysed with several banding methods and in-situ hybridization. In all species, the diploid set consists of 48 mostly acrocentric chromosomes and has a similar location (terminal centromeric) of NORs, except for L. pavo (interstitial pericentric) and P. ponticus (terminal on the long arm). There are major differences in karyotype with regard to the amount and distribution of heterochromatin. Parablennius tentacularis shows a distinctive sex-chromosome system involving 2n = 48 males with a large totally heterochromatic Y chromosome, and males with 2n = 47. This difference is likely to be the consequence of a translocation of an autosome on the original Y. This finding constitutes an additional instance of the great variability in origins of multiple sex chromosome systems in vertebrates.

Sex chromosomes, sex-linked genes, and sex determination in the vertebrate class amphibia

In this chapter the different categories of homomorphic and heteromorphic sex chromosomes, types of sex-determining mechanisms, known sex-linked genes, and data about sex-determining genes in the Amphibia have been compiled. Thorough cytogenetic analyses have shown that both XY/XX and ZW/ZZ sex chromosomes exist in the order Anura and Urodela. In some species quite unusual systems of sex determination have evolved (e.g. 0W-females/00-males or the co-existence of XY/XX and ZW/ZZ sex chromosomes within the same species). In the third order of the Amphibia, the Gymnophiona (or Apoda) there is still no information regarding any aspect of sex determination. Whereas most species of Anura and Urodela present undifferentiated, homomorphic sex chromosomes, there is also a considerable number of species in which an increasing structural complexity of the Y and W chromosomes exists. In various cases, the morphological differentiation of the sex chromosomes occurred as a result of quantitative and/or qualitative changes to the repetitive DNA sequences in the constitutive heterochromatin of the Y and W chromosomes. The greater the structural differences between the sex chromosomes, the lesser the extent of pairing in meiosis. No dosage compensation of the sex-linked genes in the somatic cells of the homogametic (XX or ZZ) individuals have been detected. The genes located to date on the amphibian sex chromosomes lead to the conclusion that there is no common ancestral or conserved sex-linkage group. In all amphibians, genetic sex determination (GSD) seems to operate, although environmental factors may influence sex determination and differentiation. Despite the accumulated evidence that GSD is operating in Anura and Urodela, there is little substantial information about how it functions. Although several DNA sequences homologous to the mammalian ZFY, SRY and SOX genes have been detected in the Anura or Urodela, none of these genes is an appropriate candidate to explain sex determination in these vertebrates.

Sex chromosome evolution in fish. II. Second occurrence of an X1X2Y sex chromosome system in Gymnotiformes

A multiple sex chromosome system of the X1X1X2X2:X1X2Y type is reported to occur in the fish species Brachyhypopomus pinnicaudatus (Gymnotiformes, Hypopomidae), being the second occurrence of this sex chromosome system in Gymnotiformes and the fifth among Neotropical freshwater fish. The possible origin of this system was hypothesized to be a centric fusion, which occurred in an ancestral form, of two medium-sized acrocentrics, giving origin to the metacentric neo-Y. Heterochromatic DAPI-positive regions were visualized in the pericentromeric region of all the chromosomes, including the Y-chromosome. In-situ hybridization with (TTAGGG)n (all-human-telomeres probe) did not detect any telomeric interstitial regions (ITS), indicating a possible loss of terminal segments of the chromosomes involved in the neo-Y formation.

Physical mapping of rDNA genes, (TTAGGG)n telomeric sequence and other karyological features in two earthworms of the family Lumbricidae (Annelida: Oligochaeta)

A cytogenetical study was carried out on the chromosomes and nuclear DNA amounts of the terrestrial earthworms Octodrilus complanatus and Eisenia foetida (Annelida: Oligochaeta: Lumbricidae). Chromosomes were studied using Giemsa staining, banding methods and fluorescent in situ hybridization (FISH) with two repetitive DNA probes [rDNA and (TTAGGG)n]. rDNA FISH and silver staining consistently identified one chromosome pair per spread in both species. The telomeric sequence (TTAGGG)n hybridized with termini of all the chromosomes in both earthworms. Flow cytometry DNA assays showed that O. complanatus and E. foetida had different nuclear DNA contents (2C value=1.72 and=1.40 pg, respectively) but very similar base composition in their genomes.

An XX/XY sex chromosome system in a fish species, Hoplias malabaricus, with a polymorphic NOR-bearing X chromosome

Cytogenetic studies were carried out in the fish, Hoplias malabaricus, from the Parque Florestal do Rio Doce (Brazil). This population is characterized by 2n = 42 chromosomes for both males and females and an XX/XY sex chromosome system, confirmed through several banding methods. Females show 24 metacentric, 16 submetacentric and 2 subtelocentric chromosomes. Males show 24 metacentric, 17 submetacentric and 1 subtelocentric chromosomes. While the X chromosome is easily recognized (the only subtelocentric element), the Y chromosome is somewhat difficult to identify but appears to correspond to the smallest submetacentric in the male karyotype. In-situ hybridization with an 18S rDNA probe showed 10 well-labeled chromosomes, including the X chromosome. The 5S rDNA is interstitially located in a single metacentric pair independent of the 18S rDNA sites. The NOR on the X chromosome is always active and occurs adjacent to a heterochromatic distal segment on the long arm. Variations in size of the NORs and/or heterochromatic segment correspond to a polymorphic size condition observed in the X chromosome. The present results confirm the XX/XY sex chromosome system in the population analyzed as well as a new cytotype in the Hoplias malabaricus group.

Ribosomal DNA location in the scarab beetle Thorectes intermedius (Costa) (Coleoptera: Geotrupidae) using banding and fluorescent in-situ hybridization

Mitotic metaphase chromosomes of the scarab beetle Thorectes intermedius (Costa) (Coleoptera Scarabaeoidea: Geotrupidae) were analyzed using various banding methods and fluorescent in-situ hybridization (FISH) with a ribosomal probe. The results obtained indicate that silver and CMA3 staining are unable to localize the chromosome sites of nucleolar organizer regions (NORs). Such an inadequacy is a consequence of the extensive silver and CMA3 stainability of both constitutive heterochromatin and heterochromatin associated to the NORs.

Evidence for heteromorphic sex chromosomes in males of Rana tagoi and Rana sakuraii in Nishitama district of Tokyo (Anura: Ranidae)

Karyotypes of the Tago brown frog Rana tagoi and stream Tago brown frog Rana sakuraii from a mountain region in the Nishitama district in Tokyo were examined by conventional Giemsa staining, C-banding and late replication (LR)-banding. Chromosome number was 2n = 26 in all cases. The 26 chromosomes consisted of five (1-5) pairs of large chromosomes and eight (6-13) pairs of small chromosomes. Chromosome 10 had a secondary constriction on the long arm. In all frogs, on chromosome pair 8, the XX/XY type sex chromosome was present. C-banding analysis indicated that, in R. sakuraii, neither the X nor Y chromosome possessed interstitial C-bands but each had centromere staining, while in R. tagoi, an interstitial C-band was present on the long arm of the X chromosome. The Y chromosome had no interstitial C-band. LR-banding analysis demonstrated the X and Y chromosomes to have a LR-band on the short arm and two LR-bands, each on the long arm, and the bands on both species to be essentially the same. Heteromorphic sex chromosomes in males of R. sakuraii and R. tagoi were identified for the first time in this study.

Cytogenetic studies in some species of Scorpaeniformes (Teleostei: Percomorpha)

Cytogenetic studies were performed in four species of two scorpaeniform teleost families: Scorpaenidae and Triglidae. The karyotypes of Trigla lucerna, Trigloporus lastoviza (Triglidae), Scorpaena porcus and S. notata (Scorpaenidae) were analysed using various banding methods and in situ hybridization with a telomeric probe. In the two Scorpaena species, modest morphological divergence corresponded to considerable karyotype reorganization, while in the two Triglidae substantial phenotypical divergence corresponded to limited chromosomal changes. These data stress the need for a taxonomical re-evaluation of these teleosts based on characters independent of morphology.

High heterochromatin content in somatic chromosomes of two unrelated species of Diplopoda (Myriapoda)

For the first time, a conventional analysis of C-banded karyotypes was carried out in two distantly related diplopod species; this revealed an impressive percentage of heterochromatin in both genomes. In Acanthopetalum sicanum (Order Callipodida) (2n = 12), heterochromatin constitutes about 60% of the total DNA in females and 56% in males, whereas in Enologus oxypygum (Order Julida) (2n = 22) it is about 67% in both sexes. Heterochromatin of the two species was found to be similar in base composition (AT rich) and heterochromatin distribution, indicating that it has accumulated in a species-specific manner. Sex-determining mechanisms of the XY type were detected in both A. sicanum and E. oxypygum. In A. sicanum, the Y presented the lowest heterochromatic content of all chromosomes in the karyotype, whereas the X presented the highest.

Polymorphism of the nucleolus organizer region (NOR) on the putative sex chromosomes of Arctic char (Salvelinus alpinus) is not sex related

Polymorphism of the nucleolus organizer region (NOR) on the putative sex chromosomes of Arctic char (Salvelinus alpinus) was examined using conventional cytogenetic and molecular techniques. Variation was observed in the number, size and position of rDNA loci on the sex pair. Fluorescence in situ hybridization (FISH) analyses showed that the sex chromosomes of Arctic char lack the repetitive DNA sequences (Mbol/BglII family) that are a prominent feature of the sex chromosomes of lake trout (S. namaycush). Southern analyses of genomic DNAs using an rDNA fragment as probe revealed extensive restriction fragment length polymorphism (RFLP) variation among individuals. Despite the presence of variation in all aspects of this rDNA locus, no sex-specific differences were detected. Repetitive DNAs (multicopy rDNA as in Arctic char or tandem repetitive DNA as in lake trout) appear to play important but different roles in the evolution of the sex chromosomes in these species.

Cytogenetics of the genus Leporinus (Pisces, Anostomidae). 1. Karyotype analysis, heterochromatin distribution and sex chromosomes

Cytogenetic analyses (Giemsa staining, C-banding, AgNO3 labelling of nucleolus organizer regions (NORs) and staining with base-specific fluorochromes) were performed on the South American fish species Leporinus friderici, L. obtusidens and L. elongatus. The overall karyotypic structure, position of NORs, as well as the amount, distribution and composition of constitutive heterochromatin were determined. Particular attention was given to the highly differentiated ZZ/ZW sex chromosome system of L. obtusidens and L. elongatus. Sharing the apparently ancient macroscopic karyotype of Anostomidae, all three species have 2n = 54 meta- or submetacentric chromosomes. NORs were found exclusively on chromosome pair 2, which may represent the ancestral NOR-bearing chromosome of the anostomid karyotype. Observed differences in the relative position of NORs along chromosome 2 and variations in the amount and distribution of constitutive heterochromatin throughout the karyotype were most probably caused by heterochromatin-mediated chromosome rearrangements. Detailed analysis of the morphologically similar heteromorphic ZZ/ZW sex chromosomes of L. obtusidens and L. elongatus allowed detection of differences in the DNA composition of the largely heterochromatic W chromosomes. However, since these and the W chromosomes of three other Leporinus species exhibit homologies with respect to their relative size, centromere position and amount and distribution of heterochromatin, it is concluded that they evolved from the same ancestral W chromosome.

Heteromorphic sex chromosomes in Eupsophus insularis (Amphibia: Anura: Leptodactylidae)

The chromosomes of the Chilean frog Eupsophus insularis are described for the first time. This species has a chromosome number of 2n = 30, and based on the karyotype it is concluded that E. insularis is closely related to E. migueli. E. insularis has an XX/XY system of sex determination, and pericentromeric constitutive heterochromatin is present in all chromosomes except in the Y chromosome. It is postulated that the Y chromosome is derived from a small ancestral metacentric chromosome that lost its heterochromatic segment.