Recurrence of Down syndrome associated with microchromosome

Summary We report a family with five members presenting an extra bisatellited microchromosome. Two of them also present trisomy 21. We discuss the relationship between trisomy and the extra chromosome.     

A microchromosome derived from chromosome 11 in a patient with the CREST syndrome of scleroderma.

A patient with the CREST syndrome of scleroderma was found to carry a mosaicism for a supernumerary microchromosome. The microchromosome was approximately 1 micron in size and present in over half of the lymphocyte metaphases examined. It bound centromeric proteins specifically recognized by CREST autoimmune sera (including the patient's serum). In situ hybridization with a panel of chromosome-specific alpha-satellite probes showed that the microchromosome was derived from chromosome 11, most or all of its chromatin consisting of the chromosome 11 subset of alpha-satellite DNA. It had no detectable telomeric sequences. Microchromosomes observed by electron microscopy had no visible free ends. The chromatin looked exactly the same as it did in normal chromosomes. Although we have no direct evidence for a circular structure, we conclude that the microchromosome originated by an interstitial deletion including the alpha-satellite DNA sequences and subsequent ring formation. The newly formed chromosomal element proved to be relatively stable somatically and was transmitted through meiosis. Since it possesses at least some structural and functional features of a centromeric region, the microchromosome can be thought of as an isolated centromere.     

Centromeric association of a microchromosome

Summary A supernumerary microchromosome measuring 0.5–1 m found in over half of the metaphases of a CREST scleroderma patient and his daughter has been characterized by various cytogenetic techniques. The microchromosome consisted of constitutive heterochromatin and contained nuclear antigens reacting with specific anti-kinetochore antibodies. The most remarkable property of the microchromosome was its non-random position: it was closely associated with the centromere of any of the normal chromosomes in the majority of the metaphases. Furthermore, an inordinately high rate of Y chromosome aneuploidy was found in the CREST scleroderma patient. The origin and structure of the microchromosome, its possible connection with the CREST variant of scleroderma, and the phenomenon of centromeric association are discussed.     

挂榜山小鲵的核型(有尾目:小鲵科)

本文首次报道了挂榜山小鲵Hynobius guabangshanensis 的核型.其2n=56,分为4组,其中9对大型染色体,4对双臂中型染色体,5对双臂小型染色体和10对单臂小型染色体.挂榜山小鲵具有池塘类型小鲵的特征,即2n=56以及缺少中端着丝粒染色体,这与挂榜山小鲵的生态和形态特征也属池塘类型相符.     

FISH mapping of 57 BAC clones reveals strong conservation of synteny between Galliformes and Anseriformes

Karyotypes of chicken (Gallus gallus domesticus; 2n = 78) and mallard duck (Anas platyrhynchos; 2n = 80) share the typical organization of avian karyotypes including a few macrochromosome pairs, numerous indistinguishable microchromosomes, and Z and W sex chromosomes. Previous banding studies revealed great similarities between chickens and ducks, but it was not possible to use comparative banding for the microchromosomes. In order to establish precise chromosome correspondences between these two species, particularly for microchromosomes, we hybridized 57 BAC clones previously assigned to the chicken genome to duck metaphase spreads. Although most of the clones showed similar localizations, we found a few intrachromosomal rearrangements of the macrochromosomes and an additional microchromosome pair in ducks. BAC clones specific for chicken microchromosomes were localized to separate duck microchromosomes and clones mapping to the same chicken microchromosome hybridized to the same duck microchromosome, demonstrating a high conservation of synteny. These results demonstrate that the evolution of karyotypes in avian species is the result of fusion and/or fission processes and not translocations.     

Gene homologs on human chromosome 15q21-q26 and a chicken microchromosome identify a new conserved segment

The genes for insulin-like growth factor 1 receptor (IGF1R), aggrecan (AGC1), β₂-microglobulin (B2M), and an H6-related gene have been mapped to a single chicken microchromosome by genetic linkage analysis. In addition, a second H6-related gene was mapped to chicken macrochromosome 3. The Igf1r and Agc1 loci are syntenic on mouse Chr 7, together with Hmx3, an H6-like locus. This suggests that the H6-related locus, which maps to the chicken microchromosome in this study, is the homolog of mouse Hmx3. The IGF1R, AGC1, and B2M loci are located on human Chr 15, probably in the same order as found for this chicken microchromosome. This conserved segment, however, is not entirely conserved in the mouse and is split between Chr 7 (Igf1r-Agc) and 2 (B2m). This comparison also predicts that the HMX3 locus may map to the short arm of human Chr 15. The conserved segment defined by the IGF1R–AGC1–HMX3—B2M loci is approximately 21–35 Mb in length and probably covers the entire chicken microchromosome. These results suggest that a segment of human Chr 15 has been conserved as a chicken microchromosome. The significance of this result is discussed with reference to the evolution of the avian and mammalian genomes. Received: 7 December 1996 / Accepted: 7 February 1997     

Isodicentric Y chromosomes and secondary microchromosomes

We report here on two mosaic patients with both an idic(Yp) and a microchromosome. FISH with the DYZ3 alphoid repeat demonstrated that the isodicentrics effectively exhibited two alphoid clusters whereas the small markers had a Y-centromere. These data, along with 4 previous observations, indicate that such microchromosomes effectively result from functional dicentricity of isodicentric Y-chromosomes and represent the excision of one centromere plus various amounts of adjacent chromatin. Other than a real infrequency of such a concurrence or a very low proportion of the cell line(s) containing the microchromosome, the paucity of observations points to a high rate of underdiagnosis as revealed by two idic(Y) instances in which the microchromosome was detected only in samples assessed by FISH.     

Karyotypic characterization of Iheringichthys labrosus (Pisces, Pimelodidae): C-, G- and restriction endonuclease banding

Various chromosomal banding techniques were utilized on the catfish, Iheringichthys labrosus, taken from the Capivara Reservoir. C-banding regions were evidenced in telomeric regions of most of the chromosomes. The B microchromosome appeared totally heterochromatic. The restriction endonuclease AluI produced a banding pattern similar to C-banding in some chromosomes; the B microchromosome, when present, was not digested by this enzyme and remained stained. G-banding was conspicuous in almost all the chromosomes, with the centromeres showing negative G-banding. When the restriction endonuclease BamHI was used, most of the telomeres remained intact, while some centromeres were weakly digested. The B chromosome was also not digested by this enzyme. The first pair of chromosomes showed a pattern of longitudinal bands, both with G-banding and BamHI; this was more evident with G-banding. This banding pattern can be considered a chromosomal marker for this population of I. labrosus.     

Segregation and transmission of chromosomes from a reciprocal translocation in Gallus domesticus cockerels

Segregation behavior of a reciprocal translocation involving the long arm of chromosome No. 1 and a microchromosome was studied in secondary spermatocytes and embryos produced by heterozygous cockerels. The types and frequencies of the various balanced and unbalanced chromosome complements were determined. Complementary products of segregation did not occur in the expected ratios of 1:1 in secondary spermatocytes. The excess of spermatocytes with deficiency of the long arm and duplication of the short arm might be the result of lagging of the long arm at meiosis I, the centromere of the long arm being derived from a microchromosome. In the samples of secondary spermatocytes and embryos 52.5% and 49.6%, respectively, contained balanced chromosome complements. A significantly higher proportion of duplications and deletions of the long arm was seen in embryos than in secondary spermatocytes. Conversely, a lower proportion of duplications and deletions of the short arm was seen in embryos than in secondary spermatocytes. Apparently, spermatogenic cells bearing different unbalanced genomic contents are not equally viable or fertile.     

Chromosomal localization of seven HSA3q13-->q23 NotI linking clones on chicken microchromosomes: orthology of GGA14 and GGA15 to a gene-rich region of HSA3

Double-color fluorescence in situ hybridization was performed on chicken chromosomes using seven unique clones from the human chromosome 3-specific NotI linking libraries. Six of them (NL1-097, NL2-092, NL2-230, NLM-007, NLM-118, and NLM-196) were located on the same chicken microchromosome and NL1-290 on another. Two chicken microchromosome GGA15-specific BAC clones, JE024F14 containing the IGVPS gene and JE020G17 containing the ALDH1A1 gene, were cytogenetically mapped to the same microchromosome that carried the six NotI linking clones, allowing identification of this chromosome as GGA15. Two GGA14-specific clones, JE027C23 and JE014E08 containing the HBA gene cluster, were co-localized on the same microchromosome as NL1-290, suggesting that this chromosome was GGA14. The results indicated that the human chromosomal region HSA3q13-->q23 is likely to be orthologous to GGA15 and GGA14. The breakpoint of evolutionary conservation of human and chicken chromosomes was detected on HSA3q13.3-->q23 between NL1-290, on the one hand, and six other NotI clones, on the other hand. Considering the available chicken-human comparative mapping data, another breakpoint appears to exist between the above NotI loci and four other genes, TFRC, EIF4A2, SKIL and DHX36 located on HSA3q24-->qter and GGA9. Based on human sequences within the NotI clones, localization of the six new chicken coding sequences orthologous to the human/rodent genes was suggested to be on GGA15 and one on GGA14. Microchromosomal location of seven NotI clones from the HSA3q21 T-band region can be considered as evidence in support of our hypothesis about the functional analogy of mammalian T-bands and avian microchromosomes.     

Microsatellites from the linkage groups E26C13 and E50C23 are located on the Gallus gallus domesticus microchromosomes 20 and 21

Using the method of dual color fluorescence in situ hybridization and a set of chromosome-specific BAC clones, localization of microsatellites LEI0345 and LEI0336 on chicken (Gallus gallus domesticus) mitotic chromosomes was performed. Microsatellite LEI0345 (TAM 32, BAC clones r49A10 and r55M23) from the linkage group E26C13 was mapped to microchromosome 20, while microsatellite LEI0336 (TAM 32, BAC clones r19E22 and r13C08) from the linkage E50C23 was assigned to microchromosome 21. Using the PCR technique, an attempt to assign the suitable markers to chromosome-specific BAC clones was made. The PCR data confirmed the microsatellite localization performed with the help of FISH technique and showed the presence of the LEI0345 microsatellite sequence on many other chicken microchromosomes, except for microchromosomes 19 and 22. Linkage groups E26C13 and E50C23 were assigned to microchromosomes 20 and 21, respectively.     

Cellular oncogenes (c-erb-A and c-erb-B) located on different chicken chromosomes can be transduced into the same retroviral genome.

Avian erythroblastosis virus has transduced two cellular genes, c-erb-A and c-erb-B. Using fractionated chicken chromosomes, we found that the two genes are located on different chromosomes in the chicken genome: c-erb-A is on a microchromosome, and c-erb-B is on a large chromosome. The locations of two other cellular oncogenes (c-fps and c-myb) were also determined: c-fps is on a microchromosome, and c-myb is on chromosome of an intermediate size. Our results suggest that avian erythroblastosis virus had transduced the two cellular genes independently, conforming to previous indications that cellular oncogenes are dispersed among multiple chromosomes in every species that has been examined.     

New evidence for nucleolar dominance in hybrids of Drosophila arizonae and Drosophila mulleri

Drosophila mulleri (MU) and D. arizonae (AR) are cryptic species of the mulleri complex, mulleri subgroup, repleta group. Earlier cytogenetic studies revealed that these species have different regulatory mechanisms of nucleolar organizing activity. In these species, nucleolar organizing regions are found in both the X chromosome and the microchromosome. In the salivary glands of hybrids between MU females and AR males, there is an interspecific dominance of the regulatory system of the D. arizonae nucleolar organizer involving, in males, amplification and activation of the nucleolar organizer from the microchromosome. The authors who reported these findings obtained hybrids only in that cross-direction. More recently, hybrids in the opposite direction, i.e., between MU males and AR females, have been obtained. The purpose of the present study was to evaluate, in these hybrids, the association of the nucleoli with the chromosomes inherited from parental species in order to cytogenetically confirm the dominance patterns previously described. Our results support the proposed dominance of the AR nucleolar organizer activity over that of MU, regardless of cross-direction.     

Microchromosomes of the Ontario Red Fox (Vulpes vulpes): Distribution of chromosome numbers and relationship with physical characteristics

Studies on the distribution of the microchromosomes of the Ontario red fox (Vulpes vulpes Linn.) were carried out on nine foxes trapped in the wild and 38 foxes maintained in captivity. The microchromosomes varied in number from zero to six resulting in variation in diploid number from 34 to 40. The most common numbers detected were 36 and 37 followed by 38, 35, 39, 40 and 34 in decreasing order of occurence. Both inter-and intra-individual variations in chromosome numbers were found.Elevated microchromosome count was noted to have a positive correlation with the body weight of captive male foxes, however no relationship was found between microchromosome number and body length of male foxes or with the weight or length of female foxes.     

Karyotypes of two rare species of hynobiid salamanders from Taiwan,Hynobius sonani (Maki) and Hynobius formosanus Maki (Urodela)

Two salamanders endemic to Taiwan, Hynobius sonani and Hynobius formosanus, are similar to Japanese hynobiids in having 2n = 58 chromosomes and by the absence of a medium-sized telocentric pair. H. sonani has 6 metacentric and 10 telocentric microchromosome pairs, while H. formosanus has 5 metacentric and 11 telocentric microchromosome pairs. The karyotype of H. sonani is nearly identical to that of the Japanese hynobiid salamander H. boulengeri. Karyophylogenetic relationships among forms of mountain-stream type hynobiids of Taiwan and Japan are discussed.This paper is dedicated to late Mr. Tadao Yamamoto who died on November 2, 1985.     

组织相容性复合体在实验鸡中的应用

鸡主要组织相容性复合体（MHC）基因位于鸡16号染色体上,具有高度的多态性。现已发现,不同MHC-B单倍体对各种疾病的抗性不同。本文主要介绍了鸡MHC的结构特点、鸡MHC与抗病性的关系、鸡MHC检测方法的研究进展以及其在鸡抗病育种中的应用前景。     

Characterization of a new repetitive sequence that is enriched on microchromosomes of turkey

We cloned and characterized a new highly repetitive, species-specific DNA sequence from turkey (Meleagris gallopavo). This repeat family, which accounts for approximately 5% of the turkey genome, consists of a 41 bp repeated element that is present in tandem arrays longer than 23 kb. In situ hybridization to turkey metaphase chromosomes (2n=80) demonstrated that this sequence was located primarily on certain microchromosomes: approximately one-third of the 66 microchromosomes showed a positive signal. With respect to the macrochromosomes, hybridization was seen only in a pericentric position on nos. 2 and 3. The turkey microchromosome (TM) sequence shares motifs (alternating A_3–5 and T_3–5 clusters separated by 6–8 bp) that have been found previously in other avian tandemly repeated elements, e.g. a chicken microchromosome sequence, and W (female) chromosome-specific sequences of chicken and turkey. However, the TM sequence does not cross-hybridize under moderately stringent conditions with these other sequence. The spread and amplification of related repetitive sequence elements on microchromosomes and W chromosomes is discussed.by E.R. Schmidt     

Heterochromatin and karyotypic differentiation of some neotropical cactus-breeding species of the Drosophila repleta species group

Metaphase chromosomes from neuroblasts of strains from both laboratory stocks and natural populations of D. serido, D. meridionalis, D. borborema and D. buzzatii have been studied using colcemid pretreatment, and air-drying followed by Giemsa staining. The two latter species both show a uniform ‘basic’ metaphase karyotype. D. serido and D. meridionalis, on the other hand, both include a number of different, geographically distinct, metaphase karyotypes involving differences in the major blocks of constitutive heterochromatin present on the sex chromosomes and/or the 6th chromosome (microchromosome). These chromosomal differences are largely due to the acquisition of extra heterochromatin though pericentric inversions appear to be responsible for some of the Y-chromosome variants in D. serido. Moreover, the cytological evidence demonstrates that populations of both species are far from continuous in distribution. The extent to which such cytological differences reflect the existence of subspecific or specific complexes with minimal morphological differentiation is under investigation.     

Somatic chromosomes of Bubulcus ibis (L.) (Cattle-Egret): A case of reciprocal translocation

The somatic chromosome complement of Bubulcus ibis consists of six pairs of macrochromosomes, twenty-three pairs of microchromosomes and a pair of sex chromosomes. The Z-chromosome is comparable in size to autosome pairs 3 and 4, from which it is difficult to distinguish, and the W-chromosome is indistinguishable from the larger microchromosomes. The chromosome complement of one individual was found to deviate from the normal because of structural heterozygosity involving a member of chromosome pair 1 and a microchromosome.