Centric Fusion Research Articles

Comparative cytogenetics of hamsters of the genus Calomyscus

Karyotypes of Calomyscus from different regions of Turkmenistan, Iran, and Azerbaijan were studied using chromosome banding (G- and C-banding) and analyses of meiosis in laboratory hybrids. Extensive variation in the diploid number and the number of autosomal arms (FNa) was revealed (2n = 30, FNa = 44; 2n = 32, FNa = 42; 2n = 44, FNa = 46; 2n = 44, FNa = 58; 2n = 37, FNa = 44; 2n = 50, FNa = 50; 2n = 52, FNa = 56). Centric and tandem fusions and heterochromatin changes were identified as the major modes of karyotype evolution in this group. Natural hybrids between individuals with different karyotypes were recorded, and regular chromosome pairing in meiosis was observed in laboratory hybrids. Fluorescence in situ hybridization with a 353-bp BspRI complex tandem repeat indicated that chromosomal repatterning occurred recently within the genus. There is no unequivocal evidence suggesting the role of chromosomal change in the speciation of the populations of Calomyscus examined.

(T2AG3)n telomeric sequence hybridization suggestive of centric fusion in karyotype marsupials evolution.

It has been suggested that the karyotype of the marsupials derived from a low diploid number (2n = 14) which originated, through fissions of biarmed chromosomes, the karyotypes with a higher 2n. The telomeric sequence (T2AG3)n was in situ hybridized to the chromosomes of Gracilinanus microtarsus and G. emiliae, Micoureus demerarae and Marmosa murina, species with 2n = 14, in Monodelphis sp., M. domestica, M. kunsi and M. brevicaudata with 2n = 18, and in Lutreolina crassicaudata, Didelphis albiventris, Chironectes minimus, Philander opossum and P. frenata, all of them with 2n = 22. The probe hybridization occurred in the telomeric regions of both arms, short and long, of all chromosomes of the complement of all individuals of all species analysed. However, in some pairs of the karyotypes of Gracilinanus microtarsus and Micoureus demerarae (with 2n = 14), and in Monodelphis sp., M. domestica, M. kunsi and M. brevicaudata (2n = 18) ectopic signs of hybridization were detected proximal to the centromeres, suggesting the retention of this telomeric sequence in the centromeric regions of some chromosomes of these species. Based on these results, it is proposed that the karyotype of marsupials evolved from a 2n = 22 to a 2n = 14, by means of chromosomal fusions.

Chromosomal characterization of three centric fusion translocations in cattle using G-, R- and C-banding and FISH technique

Abstract Five cattle, two of the Podolian breed, two Grey Alpine, and one Chianina,all of which were heterozygous carriers of three centric fusion translocations(rob-l;29, rob-4;8, rob-25;27), underwent cytogenetic investigation. The use of G-, R- and C-banding patterns, combined with the FISH technique by using both type I molecular markers and some human chromosome painting probes, allowed the precise identification of chromosomes involved in the chromosomal abnormalities,compared to previous reports. While the chromosomes involved in the well known rob (1;29) were confirmed, BTA6 (not BTA4) was involved in the second translocation. Furthermore, BTA26 and BTA29 (not BTA25 and BTA27) were involved in the third translocation. C-banding patterns confirmed the mono-centric nature of rob (1;29) and revealed the dicentric nature of both rob(6;8) and rob(26;29). The importance of these marker chromosomes in bovid chromosome nomenclatures is also discussed.

Is chromosomal speciation occurring in house mice in Tunisia?

Two chromosomal races of house mice are present in Tunisia, one represented by mice carrying the 40-acrocentric standard karyotype and the other by a Robertsonian race (2 n=22) homozygous for nine centric fusions (Rb). A comparative summary on allozyme divergence, geographical distribution and level of reproductive isolation in the Tunisian and European Rb races is presented, to which new data on mitochondrial DNA and morphological divergence are added. The Tunisian 22Rb race revealed unique features not matched by the European chromosomal races, such as a decrease in allozymic variability, a higher level of genetic and morphological differentiation and a mosaic geographical distribution. The mtDNA analysis argued in favour of a local origin of the chromosomal divergence suggesting that the higher level of differentiation between the Tunisian races resulted from the older age of the 22Rb race and/or from a severe bottleneck. The decrease in fertility of chromosomal hybrids between the Tunisian races was compatible with the limited genetic introgression between them. Furthermore, data on the restricted distribution of hybrid populations suggested that premating reproductive barriers may be evolving. The Tunisian 22Rb race is thus an appropriate model to investigate a chromosomally-mediated speciation event.

Is chromosomal speciation occurring in house mice in Tunisia?

Two chromosomal races of house mice are present in Tunisia, one represented by mice carrying the 40-acrocentric standard karyotype and the other by a Robertsonian race (2re = 22) homozygous for nine centric fusions (Rb). A comparative summary on allozyme divergence, geographical distribution and level of reproductive isolation in the Tunisian and European Rb races is presented, to which new data on mitochondrial DNA and morphological divergence are added. The Tunisian 22Rb race revealed unique features not matched by the European chromosomal races, such as a decrease in allozymic variability, a higher level of genetic and morphological differentiation and a mosaic geographical distribution. The mtDNA analysis argued in favour of a local origin of the chromosomal divergence suggesting that the higher level of differentiation between the Tunisian races resulted from the older age of the 22Rb race and/or from a severe botdeneck. The decrease in fertility of chromosomal hybrids between the Tunisian races was compatible with the limited genetic introgression between diem. Furthermore, data on the restricted distribution of hybrid populations suggested that premating reproductive barriers may be evolving. The Tunisian 22Rb race is thus an appropriate model to investigate a chromosomally-mediated speciation event.

Cytogenetic analysis of three oropharyngeal malignant melanomas in dogs

Three cases of histologically confirmed oropharyngeal malignant melanomas in dogs are presented including clinical examinations and cytogenetic analysis. Case one showed a hyperdiploid karyotype. Case two, a recurrent tumour, had a highly hypodiploid karyotype with supernumerary meta- and submetacentric chromosomes in all metaphases analysed. In the third case, a clonal fusion of chromosome 1 and 25 was observed. Comparing these results with another case of canine cutaneous melanoma as well as with human malignant melanomas reported in the literature, these tumours obviously often show cytogenetic aberrations like aneuploidy and centric fusions.

Chromosomal Relationships among Spiny Pocket Mice, Liomys (Heteromyidae), from Mexico

This study focused on differentially stained karyotypes of the heteromyids Liomys pictus pictus, L. p. plantinarensis, L. spectabilis, and L. irroratus, and described their banding patterns of euchromatin and constitutive heterochromatin to decide if results fit expectations of chromosomal rearrangements leading to karyotypic evolution of the L. irroratus, L. spectabilis, and L. pictus lineage. Results confirmed most previous findings on diploid numbers of chromosomes and fundamental numbers (except for L. irroratus). Homologous G-banding patterns allowed identification of chromosome rearrangements such as centric fusions, pericentric inversions, and addition and deletion of euchromatin. Moreover, C-banding patterns showed that amounts and distribution of constitutive heterochromatin were different among species. Differentially stained karyotypes confirmed previous reports and contributed details on chromosomal morphology. Chromosomal rearrangements found mostly support hypotheses on karyotypic changes that led to chromosomal evolution of the Liomys lineage examined, although the lineage sequence may be different.

Chromosome polymorphisms and natural selection inLeptysma argentina (Orthoptera): external phenotype affected by a centric fusion predicts adult survival

The relationship between fitness variation associated with a quantitative trait and a Mendelian factor affecting that trait was examined in a natural population of the South American grasshopperLeptysma argentina. Previous studies have shown that a centric fusion between chromosomes 3 and 6 (fusion 3/6) increases adult survival and body size in this grasshopper. Here we examined the possible relationships among fusion 3/6, a size-related trait (prothorax height) and adult survival in a natural population. The study was based on two generations, comparing samples taken at the beginning and at the end of the adult life span. All individuals were karyotyped and scored for prothorax height (PH). A nonparametric regression analysis revealed that adult survival monotonically increased with PH in both generations. Moreover, fusion 3/6 was found to have an additive effect on this trait. Within generations, fusion frequency increased with adult survival in males (but not significantly so), as expected if phenotypic selection on PH influences the fusion polymorphism. Using regression analyses, we show that the correlation between PH and adult survival is not a purely environmental correlation genetically independent from the fusion polymorphism. A simple model is proposed for testing similar hypotheses in studies of selection on a trait influenced by a known genetic polymorphism.

Synteny assignment of four genes and two microsatellite markers in river buffalo (Bubalus bubalis L.)

Synteny assignment of four genes and two microsatellite markers in river buffalo (<i>Bubalus bubalis</i> L.)

Cytotaxonomic studies of Encarsia Förster (Hymenoptera: Aphelinidae)

AbstractA cytotaxonomic study was carried out on 13 species of Encarsia Förster, known to parasitize aleyrodids and diaspidids. The chromosomes varied greatly both in number and morphology, with E. protransvena Viggiani having the lowest chromosome number (2n = 6) and E. asterobemisiae Viggiani &amp; Mazzone the highest (2n = 20). The most common chromosome number was 2n = 10. C-banding, G-banding and silver staining for nucleolar organizer regions (NOR) provided the possibility of distinguishing between karyotypes with the same chromosome number and morphology and to identify all the pairs of homologues in a diploid set for advanced cytogenetic studies. The karyotype of Coccophagus lycimnia (Walker) was also examined. The chromosome data suggested that in Encarsia, karyotype differentiation has mainly occurred through a series of centric fusions, although other rearrangements may also have been significant. The importance of karyological data in systematic studies and in the identification of biotypes and cryptic species of economic interest is outlined.

Translocations involving the short arm of chromosome 17 in chronic B-lymphoid disorders: frequent occurrence of dicentric rearrangements and possible association with adverse outcome.

Unbalanced translocations involving chromosome arm 17p, where the TP53 tumor suppressor gene localizes, are rarely described in chronic lymphocytic leukemia and small lymphocytic lymphoma (CLL/SLL), but recent use of molecular cytogenetic techniques have indicated a significant incidence of TP53 deletions, suggesting the involvement of chromosome 17p in these disorders. By conventional karyotype, we have identified unbalanced translocations involving 17p in 14 out of 123 (11%) CLL/SLL patients with clonal abnormalities. Cases were characterized by resistance to chemotherapy and a poor clinical outcome. The karyotypes presented a high incidence of complex rearrangements and 17p translocations were characterized by various partners. In 10 cases a centric fusion was assessed by fluorescent in situ hybridization (FISH) experiments using specific centromeric probes. The incidence of dicentric translocations in these series is therefore significantly higher than usually described, arising in up to 71% (10 out of 14 cases). In all cases, translocations led to a monosomy 17p and to a TP53 monoallelic deletion. The adverse clinical outcome confirms that structural abnormalities involving chromosome 17p are associated with disease progression in patients with chronic lymphoproliferative disorders.

Assignment of new loci to river buffalo chromosomes confirms the nature of chromosomes 4 and 5

Introduction Rapid development of the river buffalo physical map can be achieved by coupling its development to that of the cattle gene map. Syntenic conservation between cattle and buffalo has been demonstrated, mainly using somatic cell hybrids (de Hondt et al. 1991; El Nahas et al. 1993, 1996, 1998; de Hondt et al. 1997; El Nahta 1996; Oraby et al. 1977), and by using in situ hybridization as reviewed by Iannuzzi (1997).G‐ and R‐banding comparisons between cattle (2n = 60) and river buffalo (2n = 50) chromosomes have revealed a large number of banding homologies between the two species, both at early‐metaphase (Gupta and Ray‐Chaudhury 1978; Di Berardino et al. 1981) and prometaphase stages (Iannuzzi et al. 1990). Banding homology indicates that the five river buffalo biarmed pairs originate from centric fusion translocation between two of ten homologous cattle autosomes, which is very supportive of the hypothesis that both species have a common ancestor (Wurster and Benirschke 1968). Based on cytological analysis and banding homology between cattle and buffalo chromosomes, the five biarmed chromosomes of the river buffalo BBU1, BBU2, BBU3, BBU4, BBU5 were thought to originate from fusion of cattle chromosome (BTA) 1/25; 2/23; 8/19; 5/28; and 16/29 respectively (Iannuzzi et al. 1990; Report of the Committee for the Standardization of Banded Karyotopes of the River Buffalo 1994). However, the analysis of synteny between molecular markers assigned to different cattle syntenic groups demonstrated that BBU1 results from fusion of BTA 1 and 27 rather than 1 and 25 (El Nahas et al. 1977). This called for expanding the analysis of syntenic relationships between marker loci to confirm the nature of the other biarmed buffalo chromosomes.The purpose of this study is to test synteny between markers in buffalo and to confirm the nature of the biarmed buffalo chromosomes 4 and 5, using marker loci and somatic cell hybrids.

Centric fusion differences among Oryx dammah, O. gazella, and O. leucoryx (Artiodactyla, Bovidae)

G- and C-banded karyotypes of the genus Oryx were compared using the standard karyotype of Bos taurus. Chromosomal complements were 2n = 56 in O. gazella gazella, 2n = 58 in O. g. beisa and O. g. callotis, 2n = 56–58 in O. dammah, and 2n = 57–58 in O. leucoryx. The number of autosomal arms in all karyotypes was 58. Nearly all variation in diploid number was the result of three independent centric fusions, but one 2n = 57 specimen of O. g. gazella deviated from the normal complement of 2n = 56 due to XXY aneuploidy. A 2;17 centric fusion was fixed in O. g. gazella, whereas O. g. beisa and O. g. callotis lacked this fusion and had indistinguishable karyotypes. Oryx dammah was polymorphic for a 2;15 centric fusion, and O. leucoryx was polymorphic for an 18;19 centric fusion. The five Oryx taxa shared a fixed 1;25 centric fusion; the small acrocentric element involved in the 1;25 fusion was identified by fluorescence in situ hybridization using a cosmid specific to Bos chromosome 25. The X and Y chromosomes were also conserved among the five taxa. Oryx g. gazella differed from the other Oryx species because of the fixed 2;17 centric fusion. This difference reflects an apparently longer period of geographic isolation between O. g. gazella and other populations of Oryx, and it is consistent with the classification of O. gazella and O. beisa as distinct species (see Kingdon, 1997). The lack of monobrachial relationships among the Oryx taxa indicates that sterility barriers between species have not developed. Viability of hybrid offspring constitutes a threat to captive breeding programs designed for endangered species conservation; in the case of Oryx, the 2;15, 2;17, and 18;19 metacentrics could serve as marker chromosomes for assessing hybridization between certain Oryx taxa.

Nature and distribution of constitutive heterochromatin in fishes, genus Hypostomus (Loricariidae).

Some Hypostomus species were studied concerning the features of the karyotype structure and the constitutive heterochromatin. The karyotype of Hypostomus sp. F from the São Francisco river (Minas Gerais state, Brazil) is now described for the first time. A diversity in the diploid number, ranging from 2n = 68 to 2n = 80, as well as in the karyotype formulae, is evident in this fish group. Two types of heterochromatin, GC- and AT-rich, could be identified with the use of base-specific fluorochromes. In some species heterochromatic bands are mainly located on the centromeric and telomeric chromosomal regions, while in other species they are also observed at interstitial locations. Hypotheses concerning this heterochromatic distribution in Hypostomus karyotypes are discussed. A case of supernumerary heterochromatic segment and a centric fusion appear to be related with two variant karyotypic formulae observed among specimens from the Mogi-Guaçu and São Francisco rivers, respectively. The available data permit us to characterize a divergent karyotypic evolution among the Hypostomus species already analyzed, both at the macro- and microstructural levels, that is, their general karyotype organization and particular features related to chromosomal banding or staining, respectively.

Nonrandom segregation in multiple Robertsonian heterozygotes in the house mouse (Mus musculus domesticus): Analysis of metaphases of spermatocytes II of mice from a hybrid zone between a Robertsonian population and a population with the standard karyotype

Meiotic metaphases II from archival slides were studied in male house mice caught near Rome in a hybrid zone between a population with nine monomorphic centric fusions‐ (CD: 2n = 22) and one with the standard karyotype (2n = 40). The segregation pattern was investigated: it was found that chromosomes of the same form tended to cosegregate.

Studies of synaptonemal complexes in farm mammals--a review.

For the last 10 years extensive studies of synaptonemal complexes in farm mammals were carried out. In this article a survey of the obtained results is presented. Studies on synaptic behavior of chromosomes at pachytene substage of meiotic prophase I in carriers of centric fusions (cattle, sheep, goat, pig, and blue fox) showed that the trivalent is rarely involved in an association with the sex bivalent. In carriers of reciprocal translocations (pig and cattle) a wide range of synaptic configurations were found. Besides the expected cross-shaped quadrivalent, the following configurations were observed: open quadrivalent, trivalent plus univalent, and two heteromorphic bivalents. The latter configurations were quite frequently involved in the association with XY bivalent. Studies of synaptonemal complexes in interspecies hybrids (cattle x zebu, river x swamp buffalo, blue fox x silver fox) revealed a wide range of synaptic disturbances. Cases of pericentric inversions, aneuploidy, and chromosomal polymorphisms are also reviewed. This survey shows that synaptonemal complex analysis is a very useful tool in studies on causes of altered fertility in carriers of abnormal chromosome complement.

Telomeres and mechanisms of Robertsonian fusion.

The Robertsonian (Rb) fusion, a chromosome rearrangement involving centric fusion of two acro-(telo)centric chromosomes to form a single metacentric, is one of the most frequent events in mammalian karyotype evolution. Since one of the functions of telomeres is to preserve chromosome integrity, a prerequisite for the formation of Rb fusions should be either telomere loss or telomere inactivation. Possible mechanisms underlying the formation of various types of Rb fusion are discussed here. For example, Rb fusion in wild mice involves complete loss of p-arm telomeres by chromosome breakage within minor satellite sequences. By contrast, interstitial telomeric sites are found in the pericentromeric regions of chromosomes originating from a number of vertebrate species, suggesting the occurrence of Rb-like fusion without loss of telomeres, a possibility consistent with some form of telomere inactivation. Finally, a recent study suggests that telomere shortening induced by the deletion of the telomerase RNA gene in the mouse germ-line leads to telomere loss and high frequencies of Rb fusion in mouse somatic cells. Thus, at least three mechanisms in mammalian cells lead to the formation of Rb fusions.

Cryptic chromosomal variation in suni Neotragus moschatus (Artiodactyla, Bovidae)

AbstractThirty‐eight captive‐born suni (Neotragus moschatus) had chromosomal complements of 2n = 52–56 (fn = 60). Variation in diploid number was the result of two centric fusion polymorphisms: a 4;19 fusion and a putative 18;22 fusion. Specimens that were descendants of wild‐caught N. m. akeleyi and N. m. zuluensis were 2n = 52 and 56, respectively, but 2n = 53, 54, and 55 cytotypes were probably the result of hybridization in captivity between the two subspecies. Although populations of suni from different geographic regions are phenotypically indistinguishable, cytogenetic differences between N. m. akeleyi and N. m. zuluensis indicate that they should be recognized as distinct management units. Chromosomal variation among our panel of captive‐born specimens and evidence of higher perinatal mortality in supposed hybrid cytotypes suggest that these two subspecies be managed as separate populations, particularly with regard to captive breeding, reintroductions, and animal translocations. Insofar as our findings are restricted to the captive population, the cytogenetics of natural populations of suni should be investigated to determine if indeed N. m. akeleyi and N. m. zuluensis have fixed chromosomal differences or if the centric fusion polymorphisms found in captive animals also occur in wild suni.

Centric fusion in goats (Capra hircus): Identification of a 6/15 translocation by high resolution chromosome banding

Nine phenotypically normal Saanen goats (6 males and 3 females) belonging to the goat house of the Instituto de Biociências, UNESP, Botucatu Campus, were analyzed cytogenetically. The objective of the present study was to determine whether or not chromosomes 5 and 15 are involved in a Robertsonian translocation previously observed in a sample of a Brazilian herd using the chromosome pattern described by the ISCNDA (1989). The results suggest the involvement of chromosomes 6 and 15 in the fusion demonstrated by G-banding in prometaphase cells. The Brazilian sample of animals carrying structural rearrangements did not present any reduction in fertility, suggesting the existence of prezygotic selection against unbalanced gametes. Further investigations on the Brazilian herd are necessary to assess the real incidence of Robertsonian translocations and their effects on reproductive performance.

Centric fusion polymorphisms in waterbuck (Kobus ellipsiprymnus).

Twenty-six captive individuals of the ellipsiprymnus subspecies group of Kobus ellipsiprymnus were found to have chromosomal complements of 2n = 50-52 (FN = 61-62), and 26 of the defassa subspecies group, including three specimens from Lake Nakuru National Park, Kenya, had complements of 2n = 53-54 (FN = 62). G-banded karyotypes that were numbered according to the standard karyotype of Bos taurus revealed that variation in diploid number was the result of polymorphism for two independent centric (Robertsonian) fusions. The ellipsiprymnus group was polymorphic for a 7;11 centric fusion. Both elements of chromosome pairs 7 and 11 were fused in fusion homozygotes (2n = 50); in fusion heterozygotes (2n = 51), only one element of each pair was fused. The 7;11 fusion was lacking in specimens with 2n = 52. The defassa group was polymorphic for a 6;18 centric fusion; individuals were either heterozygous for the fusion (2n = 53) or lacking it (2n = 54). There were no defassa group individuals that were homozygous for the 6;18 fusion (2n = 52), but this may be a sampling artifact. The 6;18 fusion was fixed in the ellipsiprymnus group, whereas the 7;11 fusion was absent in the defassa group. In G- and C-banded karyotypes, all autosomal arms and the X chromosomes of the two subspecies groups appeared to be completely homologous. However, the Y chromosome was acrocentric in the ellipsiprymnus group and submetacentric in the defassa group, possibly the result of a pericentric inversion. Fixed chromosomal differences between the two subspecies groups reflect a period of supposed geographic isolation during which time they diverged genetically and phenotypically, and the centric fusion polymorphisms raise the possibility of reduced fertility in hybrids. These data, in conjunction with phenotypic and mitochondrial DNA data, suggest to us that populations of the ellipsiprymnus and defassa groups should be managed separately.