Satellite DNA sequences in the human acrocentric chromosomes: information from translocations and heteromorphisms.

Satellite III DNA has been located by in situ hybridization in chromosomes 1, 3--5, 7, 9, 10, 13--18, 20--22, and Y and ribosomal DNA (rDNA) in the acrocentric chromosomes 13--15, 21, and 22. In the acrocentric chromosomes, the satellite DNA is located in the short arm. Here we report comparisons by in situ hybridization of the amount of satellite DNA in Robertsonian translocation and "normal variant" chromosomes with that in their homologs. In almost all dicentric Robertsonian translocations, the amount of satellite DNA is less than that in the normal homologs, but it is rarely completely absent, indicating that satellite DNA is located between the centromere and the nucleolus organizer region (NOR) and that the breakpoints are within the satellite DNA. The amount of satellite DNA shows a range of variation in "normal" chromosomes, and this is still more extreme in "normal variant" chromosomes, those with large short arm (p+ or ph+) generally having more satellite DNA than those with small short arms (p- or ph-). The cytological satellites are heterogeneous in DNA content; some contain satellite DNA, others apparently do not, and the satellite DNA content is not related to the size or intensity of fluorescence of the satellites. The significance of these variations for the putative functions of satellite DNA is discussed.     

Characterization and chromosomal distribution of satellite DNA sequences of the water buffalo (Bubalus bubalis).

Satellite DNA sequences were isolated from the water buffalo (Bubalus bubalis) after digestion with two restriction endonucleases, BamHI and StuI. These satellite DNAs of the water buffalo were classified into two types by sequence analysis: one had an approximately 1,400 bp tandem repeat unit with 79% similarity to the bovine satellite I DNA; the other had an approximately 700 bp tandem repeat unit with 81% similarity to the bovine satellite II DNA. The chromosomal distribution of the satellite DNAs were examined in the river-type and the swamp-type buffaloes with direct R-banding fluorescence in situ hybridization. Both the buffalo satellite DNAs were localized to the centromeric regions of all chromosomes in the two types of buffaloes. The hybridization signals with the buffalo satellite I DNA on the acrocentric autosomes and X chromosome were much stronger than that on the biarmed autosomes and Y chromosome, which corresponded to the distribution of C-band-positive centromeric heterochromatin. This centromere-specific satellite DNA also existed in the interstitial region of the long arm of chromosome 1 of the swamp-type buffalo, which was the junction of the telomere-centromere tandem fusion that divided the karyotype in the two types of buffaloes. The intensity of the hybridization signals with buffalo satellite II DNA was almost the same over all the chromosomes, including the Y chromosome, and no additional hybridization signal was found in noncentromeric sites.     

Distribution and sequence homogeneity of an abundant satellite DNA in the beetle, Tenebrio molitor.

The mealworm beetle, Tenebrio molitor, contains an unusually abundant and homogeneous satellite DNA which constitutes up to 60% of its genome. The satellite DNA is shown to be present in all of the chromosomes by in situ hybridization. 18 dimers of the repeat unit were cloned and sequenced. The consensus sequence is 142 nt long and lacks any internal repeat structure. Monomers of the sequence are very similar, showing on average a 2% divergence from the calculated consensus. Variant nucleotides are scattered randomly throughout the sequence although some variants are more common than others. Neighboring repeat units are no more alike than randomly chosen ones. The results suggest that some mechanism, perhaps gene conversion, is acting to maintain the homogeneity of the satellite DNA despite its abundance and distribution on all of the chromosomes.     

A cloned repeated DNA sequence in human chromosome heteromorphisms

A sequence derived by ECoRI restriction of human satellite DNA III has been cloned in lambda gt WES. The cloned DNA was used as a template for in vitro synthesis of cRNA, which was hybridized in situ to preparations of human metaphase chromosomes with a range of heterochromatic polymorphisms. Most of the hybridization was found on chromosome 1, and the amount of hybridization was related to the size of the C-band on this chromosome. Hybridization to other chromosomes was not related to the C-band size, although hybridization of total satellite DNA is proportional to C-band size. Total satellite DNAs contain a mixture of sequences, some of which are predominantly located on only one pair of chromosomes. Hybridization in situ is able to discriminate between such chromosome-specific sequences and the bulk of satellite DNA. Further analysis of satellite DNAs may identify sequences specific for every chromosome pair.     

Assignment of human satellite 1 DNA as revealed by fluorescent in situ hybridization with oligonucleotides

We have used a fluorescent in situ hybridization procedure to detect human satellite 1 DNA, the simple sequence family that constitutes the non-male-specific fraction of classical satellite 1 DNA. Satellite 1 appears to be located on pericentromeric regions of chromosomes 3, 4 and 13, and on satellites of each acrocentric chromosome. These results suggest a possible relationship between quinacrine fluorescence of heterochromatin and DNA composition. Furthermore, by means of multicolour in situ hybridization, we have spatially resolved satellite 1 sequences and centromeric -satellite within heterochromatic blocks.     

Evolution of histone gene loci in chironomid midges.

In the present study we have localized the histone genes in the chromosomes of 16 different Chironomus species as well as in Prodiamesa olivacea, Glyptotendipes barbipes, and Acricotopus lucidus. In the genus of Chironomus we find four, five, or six different "major" chromosomal loci hybridizing with a histone gene cluster probe isolated from the genome of Chironomus thummi. These major histone gene loci probably contain clustered histone gene repeating units ("clustered" loci). They are located on one and the same chromosome arm in all but one of the species investigated. This shows that the histone gene clusters are rather conservative in their location over a long period of evolution. The comparison of the histone loci pattern from the chromosomes of the different chironomid species shows that there is good agreement with previously established chromosome maps and phylogenetic studies based on the chromosomal banding pattern. Stringent in situ hybridization with various histone gene containing clones suggest that the "clustered" histone gene loci are organized in a locus-specific way. In addition to the linked "clustered" histone gene loci, we found an isolated histone gene group ("orphon") present on chromosome IV in most Chironomus species. This gene group might be organized differently from the histone gene repeating unit described previously.     

The organization of the mouse satellite DNA at centromeres

The mouse genome contains a major and a minor satellite DNA family of repetitive DNA sequences. The use of 5-azacytidine has allowed us to demonstrate that these satellite DNAs are organized in two separate domains at the centromeres of mouse chromosomes. The minor satellite is closer to the short arms of the acrocentric chromosomes than the major satellite. The major satellite is farther away, flanking the minor satellite and adjacent to the euchromatic long arm of each mouse chromosome. At the level of resolution afforded by the in situ hybridization technique it would appear that the organization of the centromeric domain of the mouse is similar to that in man. That is, both contain two repetitive DNA sequence families arranged in major blocks.