Intraspecific variation in the distribution of the interstitial telomeric (TTAGGG)n sequences in Micoureus demerarae (Marsupialia: Didelphidae)

The distribution of the telomeric sequence (TTAGGG)_n was studied in chromosomes of Micoureus demerarae (2n=14), a South American marsupial, by fluorescence in-situ hybridization (FISH). The telomeric repeat sequence was present at both ends of all chromosomes, but also various interstitial telomeric sequences (ITS) were detected in the pericentromeric heterochromatic regions. Intraspecific differences in the number of ITS (2 to 8) were observed without intraindividual variation. The presence of telomere-like sequences in the same regions of constitutive heterochromatin suggest that these segments are not necessarily remnants of true telomeres resulting from chromosome rearrangements but could be part of the satellite DNA.     

Telomeric (TTAGGG)n Sequences Are Associated With Nucleolus Organizer Regions (NORs) in the Wood Lemming

The distribution of the (TTAGGG)_n telomeric sequence was studied in chromosomes of the wood lemming, Myopus schisticolor, by fluorescence in-situ hybridization. As expected, the hybridization signals were observed at telomeres of all chromosomes. However, quite a number of interstitial telomeric sites were present in the pericentric heterochromatic regions. Consistent strong hybridization signals were also seen at one terminus of chromosomes 5, 7 and 12–15. By post-hybridization G-banding and silver-staining, the large blocks of the telomeric sequences on chromosomes 5 and 12 were localized to nucleolus organizer regions (NORs). This revised version was published online in August 2006 with corrections to the Cover Date.     

Cytogenetic analyses of chromosomal rearrangements in Mus minutoides/musculoides from North-West Zambia through mapping of the telomeric sequence (TTAGGG)n and banding techniques

Three specimens of M. minutoides/musculoides from Zambia were cytogenetically studied through G- and C-banding, DAPI staining and fluorescence in-situ hybridization (FISH) with a (TTAGGG)_n telomeric sequence. Biarmed chromosomes were identified according to the current nomenclature as follows: Rb(2.7), Rb(3.12), Rb(4.5), Rb(6.8), Rb(9.16), and the sex chromosomes Rb(1.X), Rb(1.Y) and Rb(1.X_d), originated from the deleted X chromosome. One female showed the diploid number 2n=24; in the two other individuals, the Rb(9.16) occurred in a heteromorphic condition, and, accordingly, the diploid number was 2n=25. FISH showed the sites of telomeric sequences at telomeres of all the chromosomes, and in an interstitial position at the centromeres of all Robertsonian metacentrics, except one – the Rb(6.8), though the patterns of hybridization varied between chromosomes. Sex chromosome pairs, in the male and females, showed a similar C-banding pattern, but revealed clear differences after FISH. Traces of telomeric sequences were found dispersed in the whole-heterochromatic arm of the Rb(1.X_d). No visible bond between C-positive heterochromatin and telomeric sequences were detected in the other either bi- or uniarmed chromosomes, indicating that they may actually represent retained telomeres in the Robertsonian metacentrics. This revised version was published online in July 2006 with corrections to the Cover Date.     

Non-telomeric chromosome localization of (TTAGGG) n repeats in the genus Eulemur

The chromosomal distribution of the (TTAGGG)_n telomeric repetitive sequences was studied in the Malagasy species Eulemur fulvus fulvus (2n = 60), Eulemur rubriventer (2n = 50), Eulemur coronatus (2n = 46) and Eulemur macaco (2n = 44). These sequences hybridize to the telomeres of all chromosomes of the four species and also to the pericentromeres of all chromosomes of E. fulvus, E. coronatus and E. macaco, with the exception of the pericentromeres of E. coronatus and E. macaco chromosomes 9, the homeologous E. fulvus chromosomes 2 and E. macaco chromosomes 1. In E. rubriventer only a very weak signal was detected at the pericentromeres of a few chromosomes. In E. fulvus, E. coronatus and E. macaco, non-telomeric (TTAGGG)_n sequences collocalize with constitutive heterochromatin. The interspecific differences of the hybridization pattern of (TTAGGG)_n sequences at the pericentromeres suggest that E. rubriventer branched off the common trunk before amplification of endogenous (TTAGGG)_n sequences occurred in pericentromeric regions.This revised version was published online in November 2005 with corrections to the Cover Date.     

Ring chromosome 20 with loss of telomeric sequences detected by multicolour PRINS

Brandt CA, Kierkegaard O, Hindkjær J, Jensen PKA, Pedersen S. Ring chromosome 20 with loss of telomeric sequences detected by multicolour PRINS.
Clin Genet 1993: 44: 26–31. © Munksgaard, 1993
A ring chromosome 20 in a male infant with epileptic seizures, mental and somatic growth retardation, and behavioural disturbances is described. Conventional cytogenetics revealed the karyotype to be 46,XY,r(20)(pter→qter) and no signs of mosaicism were found. Fluorescence in situ hybridisation using the clone p20Z1 identified the ring to be derived from chromosome 20. By counting 111 metaphases, only 7% were found to be missing the ring. The absence of telomeric sequences in the ring chromosome was demonstrated by multicolour PRINS: a three-step PRimed IN Situ labelling technique, using unlabelled primers. A terminal deletion of both arms thus seems to be the cause of the ring formation in the proband. Bivariate flow-analysis of chromosomes verified a deletion of the ring chromosome. The clinical and cytogenetic findings are compared with previous cases. A specific ring 20 syndrome seems justified.     

Organization of ribosomal RNA genes in the fungus Cochliobolus heterostrophus

Summary The genes encoding the 17S, 5.8S and 25S ribosomal RNAs in the Ascomycete Cochliobolus heterostrophus were cloned and analyzed. They are arranged in tandemly repeated units (rDNA) either 9.0 or 9.15 kilobases in length, depending upon the strain. The 5S rRNA genes are not part of the tandemly repeated rDNA. Instead, many and perhaps all of the 5S genes are dispersed in the genome, as they are in the fungi Neurospora, Aspergillus and Schizosaccharomyces. Comparative restriction maps of the rDNA from C. heterostrophus and other filamentous fungi and yeasts are presented. A survey of rDNAs from twenty-three field isolates of C. heterostrophus collected worldwide demonstrated that each isolate has one or the other of two rDNA forms, which differ in length and in the presence or absence of at least three restriction enzyme sites. The differences are all located in spacer DNA outside the coding regions for the rRNA genes. Heterogeneity in the rDNA repeat was not observed within any single isolate. The copy number of the rRNA gene cluster in C. heterostrophus is approximately 130 per haploid genome.     

Cytogenetics of a new cytotype of African Mus (subgenus Nannomys) minutoides (Rodentia, Muridae) from Kenya: C- and G- banding and distribution of (TTAGGG) n telomeric sequences

We present the results of a cytogenetic study on Mus (Nannomys) minutoides from Kenya by means of C- and G- banding and in-situ fluorescence hybridization (FISH) to localize the telomeric sequences. The karyotype is characterized by the occurrence of several Rb chromosomes Rb(1.X), Rb(1.Y). Rb(2.17), Rb(3.13), Rb(4.10), Rb(5.11), Rb(6.7), Rb(8.12), not previously described for this species. This finding suggests a high level of chromosomal diversification, which means it is possible to consider this cytotype as a new, well-differentiated, chromosomal lineage within the subgenus. The C-banding of the metaphases illustrated conspicuous blocks of centromeric heterochromatin at the paracentromeric regions of all telocentric chromosomes. Centromeric heterochromatin is not visible on all biarmed chromosomes. Following hybridization with telomeric probes, bright interstitial telomeric sequence (ITS) fluorescence signals are evident at the pericentromeric area of all Rb chromosomes, with the exception of Rb(2.17). Considering the localization of the C-positive heterochromatin and of the telomeric sequences, the events leading to the Kenyan cytotype from an all-telocentric condition probably included two steps: first, fusion without loss of heterochromatin and pericentromeric telomeric sequences; second, the reduction of the C-positive satellite DNA followed by the amplification of telomeric sequences in the C-negative paracentromeric region of Rb chromosomes. The presence of a single Rb(2.17) without ITS indicates possible variations of this mechanism.     

Identification of mutations in the ribosomal protein L5 (RPL5) and ribosomal protein L11 (RPL11) genes in Czech patients with Diamond‐Blackfan anemia

Diamond‐Blackfan anemia (DBA) is a congenital red blood cell aplasia that is usually diagnosed during early infancy. Apart from defects in red blood cell maturation, the disorder is also associated with various physical anomalies in 40% of patients. Mutations in the ribosomal protein (RP) S19 are found in 25% of patients, while mutations in other proteins of the small ribosomal subunit—RPS17 and RPS24—have been found in a fraction of patients. Recently, mutations in RPL5, RPL11, and RPL35a of the large ribosomal subunit have also been reported in several DBA patients. Here, we present the identification of mutations in the RPL5 and RPL11 genes in patients from the Czech DBA Registry. Mutations in RPL5 were identified in eight patients from 6 out of 28 families (21.4%), and mutations in RPL11 in two patients from 2 out of 28 families (7.1%). Interestingly, all 10 patients with either an RPL5 or RPL11 mutation exhibited one or more physical anomalies; specifically, thumb anomalies (flat thenar) were always present, while no such anomaly was observed in seven patients with an RPS19 mutation. Moreover, 9 out of 10 patients with either an RPL5 or RPL11 mutation were born small for gestational age (SGA) compared to 3 out of 7 patients from the RPS19‐mutated group. These observations may suggest that mutations, at least in RPL5, seem to generally have more profound impact on fetal development than mutations in RPS19. Since RPL5 and RPL11, together with RPL23, are also involved in the MDM2‐mediated p53 pathway regulation, we also screened the RPL23 gene for mutations; however, no mutations were identified. Hum Mutat 0, 1–7, 2009. © 2009 Wiley‐Liss, Inc.     

Intrachromosomal distribution of telomeric repeats in Eumops glaucinus and Eumops perotis (Molossidae, Chiroptera)

The location of chromosomal telomeric repeats (TTAGGG)_n was investigated in two species of the Molossidae family, Eumops glaucinus and Eumops perotis. The diploid chromosome number (2n) is 40 in E. glaucinus and 48 in E. perotis and the fundamental numbers (FN) are 64 and 58, respectively. It has been suggested that the E. glaucinus karyotype has evolved from the E. perotis karyotype through Robertsonian fusion events. In the present study, the telomeric sequences were detected at the termini of chromosomes in both species. In addition, E. glaucinus also displayed telomeric repeats in centromeric and pericentromeric regions in almost all biarmed chromosomes. Conversely, in E. perotis pericentromeric signals were only observed in two biarmed chromosomes. In both E. glaucinus and E. perotis, such telomeric sequences were observed as part of the heterochromatin. The interstitial sites of telomeric sequences suggest that they are remnants of telomeres of ancestral chromosomes that participated in the fusion event.     

Unusually high amount of inactive ribosomal DNA in the grasshopper Stauroderus scalaris

Fluorescence in-situ hybridization (FISH) was employed to determine the chromosomal location of the ribosomal DNA cistrons in spermatocytes of two populations of the grasshopper Stauroderus scalaris. The results showed that paracentromeric C-bands, which in this species constitute about 50% of the total chromatin, contain substantial amounts of rDNA in all chromosomes. However, silver impregnation showed the presence of a single active nucleolus organizing region (NOR) in chromosome 3 of primary spermatocytes, indicating an extremely high amount of silent rDNA across the whole genome of this species in the two geographically distant populations analysed. The significance of such an unusual phenomenon is discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Incidence of SUC-RTM telomeric repeated genes in brewing and wild wine strains of Saccharomyces

When over-expressed, RTM yeast genes confer resistance to the toxicity of molasses. They are found in distiller's and baker's industrial yeasts in multiple copies, scattered on the telomeres and physically linked to the telomeric SUC genes. Because these genes are absent from some laboratory strains, we explored the genomes of other industrial yeasts (brewing strains) and wine wild strains. A collection of 47 wine yeast strains (S. cerevisiae and S. bayanus) and 15 brewing strains, lager, ale and possible ancestors (S. monacensis, S. paradoxus and S. carlsbergensis) were screened for the presence of RTM genes. Only three wine strains and all brewing strains proved to contain RTM sequences in different copy numbers. PCR and chromosome blotting confirm the presence of SUC sequences in tandem with RTM. Moreover, analysis of the entire S. cerevisiae genome sequence shows that three other, non-telomeric, genes related to RTM are scattered on different chromosomes. Received: 4 December 1996     

In wheat ctDNA,segments of ribosomal protein genes are dispersed repeats,probably conserved by nonreciprocal recombination

Summary Some dispersed repeated sequences and their flanking regions from wheat and maize ctDNAs have been characterized. Two sets of wheat ctDNA repeats were found to be the chloroplast ribosomal protein genesrpl2 andrpl23, plus nonfunctional segments of them, designatedrpl2 andrpl23. Pairwise comparisons were made between the wheatrp123 andrpl23, and the maizerp123 sequences. The precise patterns of homology suggest that the divergence of the wheat and maize nonfunctional (rpl23) sequences is being retarded by nonreciprocal recombination, biased by selection for individuals with functional (rpl23) sequences. The implied involvement of these sequences in mechanisms of homologous recombination, and therefore in the creation and spread of new ctDNA variants, is discussed.     

Centromere-telomere (12;8p) fusion, telomeric 12q translocation, and i(12p) trisomy

The concurrence of a short arm isochromosome and a translocation of the entire long arm of the same chromosome to a telomere of another chromosome, implying trisomy for 4p, 5p, 7p, 9p, 10p or 12p, has been described in 13 patients. We have now used fluorescence in situ hybrization (FISH) to better characterize one of these rearrangements in which 12q was translocated to 8pter, whereas 12p was converted into an isochromosome. An alphoid centromere-12 repeat gave a strong signal on the i( 2p) and a weak but distinct signal at the breakpoint junction of the der(8), whereas the pantelomeric probe revealed three clear hybridization sites on the der(8): one at each end and another at the breakpoint junction. These findings suggest that the prime event was a post-fertilization centric fission of chromosome 12 leading to the 12q translocation via a real centromere telomere fusion and the i(12p). Alternatively, the crucial event may have been a centromere telomere recombination. An interstitial telomere has been documented by means of FISH at the breakpoint junction of the sole derivative usually present in 20 constitutional translocations including eight with a jumping behavior. In addition, six other telomeric translocations defined by banding methods, including another case of 12q translocation/i(12p), have also been jumping ones. These telomeric translocations have been de noro events and their proneness to exhibit a jumping behavior appears to be independent of the involved chromosomes, size of the translocated segments, and concomitant abnormalities.