Early ontogeny of aquarium-raised Moenkhausia sanctaefilomenae (Characiformes: Characidae)

The ontogeny of the characiform fish Moenkhausia sanctaefilomenae, from early embryogenesis through the early larval period, is presented. Fertilized eggs were slightly elliptical, measured 0.6 mm in diameter, and were surrounded by a fertilization envelope 0.8 mm in diameter. Much of the early embryogenesis is complete after 12 h, with cleavages complete after 2.5 h and gastrulation complete after 3 additional hours. The initial formation of organs needed for predatory behaviors occurs within 72 h. Growth of the cranial elements is quite dramatic and allows for the capture of relatively large prey at the onset of exogenous feeding. Elaboration of these elements continues into the early larval period.     

Karyotype analysis,nucleolus organizer regions and C-banding pattern of Eisenia foetida (oligochaeta,lumbricidae)

The diploid number 2n=22 and haploid number n=11 found for Eisenia foetida from Palermo, Italy, confirm earlier data for this species from other localities. Analyses of silver-stained and C-banded mitotic and meiotic chromosomes suggest that a single chromosome pair has active NORs which correspond with C-positive regions. The occurrence of nucleolus activity during spermatogenesis of E. foetida is ascertained.     

Uncovering the Ancestry of B Chromosomes in Moenkhausia sanctaefilomenae (Teleostei,Characidae)

B chromosomes constitute a heterogeneous mixture of genomic parasites that are sometimes derived intraspecifically from the standard genome of the host species, but result from interspecific hybridization in other cases. The mode of origin determines the DNA content, with the B chromosomes showing high similarity with the A genome in the first case, but presenting higher similarity with a different species in the second. The characid fish Moenkhausia sanctaefilomenae harbours highly invasive B chromosomes, which are present in all populations analyzed to date in the Parana and Tietê rivers. To investigate the origin of these B chromosomes, we analyzed two natural populations: one carrying B chromosomes and the other lacking them, using a combination of molecular cytogenetic techniques, nucleotide sequence analysis and high-throughput sequencing (Illumina HiSeq2000). Our results showed that i) B chromosomes have not yet reached the Paranapanema River basin; ii) B chromosomes are mitotically unstable; iii) there are two types of B chromosomes, the most frequent of which is lightly C-banded (similar to euchromatin in A chromosomes) (B₁), while the other is darkly C-banded (heterochromatin-like) (B₂); iv) the two B types contain the same tandem repeat DNA sequences (18S ribosomal DNA, H3 histone genes, MS3 and MS7 satellite DNA), with a higher content of 18S rDNA in the heterochromatic variant; v) all of these repetitive DNAs are present together only in the paracentromeric region of autosome pair no. 6, suggesting that the B chromosomes are derived from this A chromosome; vi) the two B chromosome variants show MS3 sequences that are highly divergent from each other and from the 0B genome, although the B₂-derived sequences exhibit higher similarity with the 0B genome (this suggests an independent origin of the two B variants, with the less frequent, B₂ type presumably being younger); and vii) the dN/dS ratio for the H3.2 histone gene is almost 4–6 times higher for B chromosomes than for A chromosome sequences, suggesting that purifying selection is relaxed for the DNA sequences located on the B chromosomes, presumably because they are mostly inactive.     

Intrapopulational polymorphism of nucleolus organizer regions in Serrapinnus notomelas (Characidae, Cheirodontinae) from the Paraná River

Analysis of the nucleolus organizer regions by silver nitrate (AgNOR), fluorescent in situ hybridization (FISH) and C-banding of Serrapinnus notomelas from the Paraná River, PR, Brazil revealed intrapopulational polymorphisms that could be classified into six patterns (I–VI). Pattern I consisted of a single nucleolus organizer region (NOR) on chromosome pair 26 with at least one active homologue, indicating that it was a preferential NO. This NOR was also present in all the other patterns. In addition, seven other variable pairs appeared in patterns II–VI. These polymorphisms may indicate transpositions of rDNA genes, located on pair 26, to various sites in the genome. These transpositions may be due to transpose mechanisms or reinsertion into sites that have sequences homologous with the inserts. C-band analysis also reflected this variability and confirmed the various patterns described here.     

Chromosome characterization in Acestrorhynchinae and Cynopotaminae (Pisces, Characidae)

The karyotypes of six species of Acestrorhynchinae ( Acestrorhynchus alus, A. lacustris, Oligosarcus hepsetus, O. jenynsii, O. macrolepis and O. pinloi ) and of one species of Cynopotaminae ( Galeocharax knerii ) were studied. The six Acestrorhynchinae species have 2 n = 50, while Galeocharax knerii has 2 n = 52 chromosomes. Some chromosomal characteristics were detected which permit establishing some karyotypic relationships among the different species investigated. Thus, among the Acestrorhynchinae, the four Oligosarcus species are relatively more related to one another than the two Acestrorhynchus species, at least with respect to the cytogenetic data considered. On the basis of the methods used, no sex chromosome heteromorphism was detected in the species for which a comparative study between male and female specimens was possible.     

Accentuated polymorphism of heterochromatin and nucleolar organizer regions in Astyanax scabripinnis (Pisces, Characidae): tools for understanding karyotypic evolution

Astyanax scabripinnis has been considered a species complex because it presents high karyotypic and morphological variability among its populations. In this work, individuals of two A. scabripinnis populations from different streams in the same hydrographic basin were analyzed through C‐banding and AgNOR. Although they present distinct diploid numbers, they show meta and submetacentric chromosome groups highly conserved (numerically and morphologically). Other chromosomal characteristics are also shared by both populations, as the pattern of constitutive heterochromatin distribution (large blocks in the telomeric regions of subtelocentric and acrocentric chromosomes) and some nucleolar chromosomes. Inter‐individual variations both in the number and size of heterochromatic blocks, and in the number and localization of NORs were verified in the studied populations, characterizing them as polymorphics for these regions. The mechanisms involved in the dispersion of heterochromatin and NORs through the karyotypes, as well as the possible events related to the generation of polymorphism of those regions are discussed. Furthermore, relationships between these populations and within the context of the scabripinnis complex are also approached. This revised version was published online in July 2006 with corrections to the Cover Date.     

Analysis of nucleolus organizer regions (NORs) in mitotic and polytene chromosomes ofPhaseolus coccineus by silver staining and Giemsa C-banding

Chromosomes with active nucleolus organizer regions (NORs) were visualized in root tip metaphases ofPhaseolus coccineus using the silver staining technique. A mean number of 5.5 Ag-NORs per cell was observed in 54 cells from eight plants. In the endopolyploid nuclei of the suspensor the silver technique did not demonstrate the reported specificity for nucleolus organizer activity, because there was usually pale staining of nucleoli and preferential staining of heterochromatic regions in the polytene chromosomes including pericentromeric material, telomeres and NORs. The mean number of NORs per nucleolus as detected by this method was 5.8 (28 nucleoli analysed). Using a modified preparation technique, giant chromosomes stained pale, but nucleoli of suspensor cells displayed darkly silver staining internal domains, each of which originating from a nucleolus organizer.—Giemsa C-banding of endopolyploid suspensor nuclei revealed C-positive nucleolus organizers with darkly staining intranucleolar fibrils. The latter were frequently involved in inter-NOR associations. In 34 nucleoli analysed, the mean number of Giemsa C-positive NORs per nucleolus was 6.0.Dedicated to Professor Dr.Lothar Geitler on the occasion of his 80th birthday.     

Genetic studies on nucleolus organizer regions (NORs) in cattle

Experimentally produced monozygotic twins, natural opposite sex blood chimeras (freemartins), and several pedigrees were used to evaluate the genetic influences on the nucleolus organizer region (NOR) patterns in cattle. In monozygotic twins, the NOR patterns of both twins are extremely similar. In chimeras, NOR patterns of genetically identical, peripheral blood lymphocytes (PBL) from the two partners resemble each other. In contrast, genetically different PBL (sib organ) differ significantly in the same environment. A high heritability of the individual NOR patterns is also demonstrated in our 23 pedigrees. In conclusion, our data demonstrate that variation in NOR expression is predominantly due to genetic factors.     

Ectopic nucleolus organizer regions (NORs) in human testicular tumors

Investigation of nucleolus organizer regions (NORs) in hematopoietic malignancies has indicated that the distribution and rearrangement of these regions may be more important in malignant tissues than is their number. In one of the few studies thus far reported on NORs in human solid tumors, we describe here Ag-NORs in a group of human testicular germ-cell tumors and the corresponding patients. Four of seven malignancies demonstrated consistent ectopic NORs; explanations could include chromosomal rearrangement (insertion?) or derepression of preexisting inactive NORs.     

Relationship between measured chromosome distribution parameters and Ag-staining of the nucleolus organizer regions

Summary Trypsin-banded metaphase plates provided by one whole blood culture of a normal adult female were analyzed as to the chromosome distribution by measuring: (1) distances between centromeres; (2) angles formed between a centromere, the gravity center of the metaphase plane, and a second centromere; and (3) the measured tendency to associate, as defined by Galperin (1969b). These data are correlated with Ag-NOR staining findings obtained from 72 cells from another culture of the same individual. In these cells, the chromosome pairs are identified using a simultaneous Ag-NOR staining and acridine orange banding technique. The silver precipitation is also correlated with the scored satellite associations in these cells. The results show a correlation between all concerned parameters, indicating that the nucleolar function of the human acrocentric chromosomes, as demonstrated by the silver precipitation technique, is probably one of the major determinants of the proximity of these chromosomes. There is a pronounced correlation of the Ag-NOR findings with those measured parameters which describe best the preferential small distances between chromosomes (angle analysis and tendency to associated data). Moreover, the association patterns of the acrocentrics with small amounts of NOR provide some evidence for the interference of other determinants cogoverning the position of the human D-and G-group chromosomes.To whom offprint requests should be sent     

Activity of nucleolus organizer regions (NORs) in embryonic livers from twin minks]

Ag-NOR patterns were studied in hepatocytes from nine mink embryo siblings, including a pair of monochorionic (presumably monozygotic, MZ) twins. Both the number and the size of Ag-NORs per cell were found to be identical in MZ twins. All the other sibs had the patterns different from each other and from the MZ ones. The conclusion is that the NORs activity is a strongly inherited character and the Ag-NOR pattern can be used as a reliable genetic marker to distinguish the twin zygosity.     

Molecular phylogeny of Moenkhausia (Characidae) inferred from mitochondrial and nuclear DNA evidence

Moenkhausia is one of the most speciose genera in Characidae, currently composed of 75 nominal species of small fishes distributed across South American hydrographic basins, primarily the Amazon and Guyanas. Despite the large number of described species, studies involving a substantial number of its species designed to better understand their relationships and putative monophyly are still lacking. In this study, we analysed a large number of species of Moenkhausia to test the monophyly of the genus based on the phylogenetic analysis of DNA sequences of two mitochondrial and three nuclear genes. The in‐group included 29 species of Moenkhausia, and the out‐group was composed of representatives of Characidae and other members of Characiformes. All species of Moenkhausia belong to the same clade (Clade C); however, they appear distributed in five monophyletic groups along with other different genera, which means that Moenkhausia is polyphyletic and indicates the necessity of an extensive revision of the group.     

Populational polymorphisms in silver staining of nucleolus organizer regions (NORs) in human acrocentric chromosomes

Summary The Ag stainability of the nucleolus organizer region (NOR) was studied in the acrocentric chromosomes identified by Q banding of cultured lymphocytes in 41 karyotypically normal persons (33 males and 8 females) originating from southeast Estonia. The data obtained are compared with those established earlier for a combined Vienna-Ulm population of 51 karyotypically normal persons (see Mikelsaar et al., 1977a). Significant differences between the two populations in the frequency and patterns of Ag-positive NORs were found. The following findings were most striking: the frequency of Ag-positive NORs in chromosome 14 and in the totals was significantly lower in the Estonian population than in the Vienna-Ulm population (P<0.01). The average modal number of Ag-positive NORs per individual was 7.8 in the Estonian population and 8.7 in the Vienna-Ulm sample (P<0.01). If the data of the two populations were combined the frequency of positive NORs was significantly (P<0.05) lower in chromosome 22 than in 13,15, and 21, but not 14.     

Conventional karyotype, nucleolar organizer regions and genome size in five Mediterranean species of Syngnathidae (Pisces, Syngnathiformes)

Conventional karyotypes, NOR-bearing chromosomes by means of silver impregnation and genome size were investigated in five Mediterranean species in three genera of the Syngnathidae. A karyotype of 48 subtelocentric-acrocentric chromosomes was found in the seahorse Hippocampus hippocampus (FN=48) while a diploid value of 44 occurred in H. guttulatus (2 sm-m+42 a; FN=46) and the pipefish Syngnathus abaster (44 a; FN=44) and S. typhle (44 a; FN=44). The pipefish Nerophis ophidion , possessing a diploid chromosomal set of 58 made up of 50 meta-submetacentric and eight subteloacrocentric elements (FN=108) and a genome size three to four times larger than those known to date, differs cytogenetically from all other Syngnathids studied so far. A single pair of active NOR-bearing chromosomes was found in both species of the genus Hippocampus while in Syngnathus and Nerophis species more than two silver positive chromosomes were found to be involved in nucleolus organization giving rise to NOR-bearing chromosome polymorphism. The possible evolutionary routes of quantitative and qualitative changes in chromosome and DNA are discussed. The resulting phylogenetic scheme is shown to coincide with that constructed from morphological characters.     

Supernumerary chromosomes in a Rhamdia hilarii population (Pisces,Pimelodidae)

A study was conducted on the chromosomes of a Rhamdia hilarii (Pisces, Pimelodidae) population. The results suggest that the basic chromosome number is 2n=58, with numerical variation up to a limit of 2n=63, due to the presence of supernumerary chromosomes which seem to be mitotically stable. These chromosomes are metacentrics and can be different in size. The C-banding pattern, showing heterochromatin especially in both telomeric regions, permits their identification in the karyotype. The NORs are located on secondary terminal constrictions on the short arm of a pair of subtelocentric chromosomes. However, there may be heteromorphism in the size of the secondary constrictions and, consequently, in the size of the NORs.     

Molecular cytogenetics and characterization of a ZZ/ZW sex chromosome system in Triportheus nematurus (Characiformes, Characidae)

Chromosomes of Triportheus nematurus, a fish species from family Characidae, were analyzed in order to establish the conventional karyotype, location of C-band positive heterochromatin, Ag-NORs, GC- and AT-rich sites, and mapping of 18S and 5S rDNA with fluorescence in situ hybridization (FISH). The diploid number found was 2n = 52 chromosomes in both males and females. However, the females presented a pair of differentiated heteromorphic chromosomes, characterizing a ZZ/ZW sex chromosome system. The Z chromosome was metacentric and the largest one in the karyotype, bearing C-positive heterochromatin at pericentromeric and telomeric regions. The W chromosome was middle-sized submetacentric, appearing mostly heterochromatic after C-banding and presenting heterogeneous heterochromatin composed of GC- and AT-rich regions revealed by fluorochrome staining. Ag-NORs were also GC-rich and surrounded by heterochromatic regions, being located at the secondary constriction on the short arms of the second chromosome pair, in agreement with 18S rDNA sites detected with FISH. The 18S and 5S rDNA were aligned in tandem, representing an uncommon situation in fishes. The results obtained reinforce the basal condition of the ZZ/ZW sex system in the genus Triportheus, probably arisen prior to speciation in the group.     

Chromosome mechanisms of sex determination,G- and C-band patterns and nucleolus organizer regions in Tropidurus torquatus (Sauria,Iguanidae)

The mitotic and meiotic chromosomes of two groups of the iguanid lizard Tropidurus torquatus were studied after conventional staining, G- and C-banding and silver staining of nucleolar-organizer regions. Karyotypic variations involving the microchromosomes were observed in both groups and are, probably, related to the mechanisms of sex determination of the X₁X₂Y/X₁X₁X₂X₂ type in the one group, and of the XY/XX type in the other.