Centromeric Constitutive Heterochromatin Research Articles

Single Cd band in dicentric translocations with one suppressed centromere

Six human dicentric translocations involving the presence of a suppressed centromere were studied: one case of t dic(9;22), one of t dic(13;18), one of t dic(14;15), and three of t dic(13;14). All exhibited chromatid separation at an acrocentric centromere and were demonstrated to have two regions of centromeric constitutive heterochromatin. The four that were available for retrospective study showed a single Cd band, with absence of the Cd band at the suppressed centromere.

Localization of Drosophila nasutoides satellite DNAs in metaphase chromosomes.

Metaphase chromosomes of D. nasutoides were hybridized in situ with 3H-cRNA synthesized from the four satellites which make up 50--60% of the total DNA of this species. All four satellites were localized in the large, metacentric, heterochromatic chromosome four. They did not, however, appear to hybridize to centromeric or other constitutive heterochromatin, nor did they, with the exception of satellite I, seem to hybridize in the specific regions of chromosome four which, on the basis of C, Q, and H banding and AT contents, were predicted to contain some of these satellites.--Comparison of grain patterns with the results of fluorescent staining indicated that satellite-bearing heterochromatin was not always associated with other fractions of constitutive heterochromatin in interphase nuclei and was, at least partially, decondensed in some larger nuclei.

Supernumerary small ring chromosome.

A supernumerary small ring chromosome was found in 30% of cultured peripheral leucocytes and 50% of skin fibroblasts in a 6-year-old boy with mild mental retardation and midline cleft palate....

A Robertsonian Translocation and its Effect upon Fertility in Brown Swiss Cattle

Metaphase chromosomes derived from leukocyte cultures of peripheral blood were observed in 299 head of Brown Swiss cattle. A Robertsonian translocation (centric fusion) was found in 31 of the animals. Estimated from this small sample 2.4% of animals of the Brown Swiss breed carry the translocation. Chromosome measurements and analysis of G-banded chromosomes proved inconclusive in identification of the homologue to the short arm of the translocation chromosome. The long arm was homologous to the longest acrocentric autosome. By C-banding, a single, small area of centromeric constitutive heterochromatin on the translocation chromosome indicated a single centromere. The translocation in Brown Swiss may be homologous to the 1/29 Robertsonian translocation in many other breeds of cattle. The translocation chromosome appeared to have segregated normally from its homologues. Aneuploid karyotypes were not observed. Analyses of breeding data failed to detect any decrease in fertility of translocation heterozygous females as compared to females of the normal karyotype. It would be premature to recommend a selection program against this translocation in Brown Swiss, but widespread use of sires heterozygous for the translocation should not be encouraged.

Non-histone protein associated with centromeric heterochromatin in the mouse chromosome

Distribution of protein in cytological preparations of the mouse metaphase chromosome was studied using protein-specific fluorochroming with dansyl chloride. Dansyl-fluorescence was relatively uniform along the axis of untreated chromosomes. After treatment of air-dried chromosome preparations with 0.2 N HCl, dansyl-fluorescence in chromosomes was remarkably reduced; it exhibited, however, bright fluorescent blocks at centromeric regions in almost all chromosomes. The same situation was observed in the male meiotic chromosomes at diakinesis; the Y chromosome seemed to lack bright dansyl-fluorescent block at the centromere after 0.2 N HCl extraction. The bright dansyl-fluorescent blocks in chromosomes after HCl or NaCl treatment occupied the same regions as C-bands. These observations suggested that centromeric constitutive heterochromatin in the mouse chromosome was associated with particular non-histone protein.

Constitutive heterochromatin of Indian muntjac chromosomes revealed by DNAse treatment and a C-banding technique.

A karyotype of a female Indian muntjac, Muntiacus muntjak vaginalis, was described. The karyotype was unique in that No. 1 and No. 3 homologous pairs were heteromorphic with respect to the size of their secondary constrictions. In these pairs, one of the homologs always had a longer secondary constriction than that on the corresponding homolog. Heterochromatin in the secondary constriction region was visualized with difficulty by a C-banding technique, but was demonstrated clearly by a DNase treatment followed by Giemsa staining, which also revealed the size difference of the secondary constriction. Centromeric constitutive heterochromatin of No. 1 chromosome was also found to differ in size between the homologs. On the basis of the heteromorphic character of No. 3 chromosome, or an X-autosome complex, it was possible to confirm autoradiographically that X-inactivation had occurred at random.

The chromosomal localisation of human satellite DNA I.

The major concentrations of human satellite DNA I (1.688 g/ml) have been localised on human chromosome preparations by the technique of in situ hybridisation using radioactive complementary RNA synthesised in vitro. Chromosomes were identified by prior study using quinacrine fluorescence microscopy. The satellite DNA is concentrated, mainly in centromeric constitutive heterochromatin, on many chromosomes but is especially obvious in the fluorescent distal segment of the Y chromosome.

Distribution of constitutive heterochromatin in HeLa and HEp-2 cell lines.

Despite the fact that HeLa and HEp-2 cell lines have been established respectively from a female and a male patient, the frequent loss of the Y chromosome makes it difficult to discriminate the two cell types. The technique of centromeric localization of heterochromatin, however, facilitates more definite identification of the two cell types. Giemsa positive centromeric constitutive heterochromatin blocks were induced within the intact metaphase chromosome preparations of Hela and HEp-2 cells. The Hela cell population had a single heterochromatin marker chromosome, whereas the HEp-2 cell line was found to possess two types of heterochromatin markers. The distinctive patterns of distribution of constitutive heterochromatin of these three chromosomes served as the guides in tracing the presumptive cytological pathways for their orgin.