DNA cloning and hybridization in deer species supporting the chromosome field theory

Localization of cloned, repetitive DNA sequences in deer species and its implications for maintenance of gene territory

The deer family shows the largest variation in chromosome number known in mammals (2n = 6 to 2n = 70). The drastic rearrangement of the chromosomes allows to test the prediction, based on the chromosome field theory, according to which DNA sequences tend to occupy specific territories within the eukaryotic chromosome. Nuclear DNAs were isolated from eight Deer and two Bovidae species. These DNAs were cleaved with the restriction enzymes Eco RI and Alu I. Following Eco RI digestion highly repetitive sequences formed two bands which were common to all deer species. These bands had about 1520 and 2240 base pairs and were particularly clear in Capreolus capreolus (2n = 70, roe deer). The 1520 band DNA was cloned in plasmid pUC9, nick translated, and hybridized with the DNAs of all ten species. The Capreolus DNA showed a high homology with the DNAs of all the species including the Indian muntjac (Muntiacus muntjak, 2n = 7, male) and the Chinese muntjac (Muntiacus reevesi, 2n = 46). 3H hybridization was carried out in situ with metaphase chromosomes of Cervus elaphus (2n = 68, red deer), M. muntjak, and M. reevesi. In C. elaphus all the chromosomes are heavily labeled except the regions of the arms near the centromere. In the muntjacs all chromosomes and most regions appear to be labeled. These results were checked with a different technique that involved the use of two antibodies and biotin labeling of the DNA. The hybridization picture was essentially the same as obtained with 3H. These results disclose that the 1520 bp DNA piece maintains its main territory independently of the drastic changes in chromosome number.

Telomeric location of retroviral oncogenes in humans

The position relative to centromeres and telomeres has been investigated in 42 proto-oncogenes that have been localized in specific bands of the human chromosomes. It turned out that the 26 retroviral oncogenes had a predominant telon territory (near telomeres). The difference from the non-retrovirally transduced oncogenes is significant (p less than 0.01). Moreover, all oncogenes studied avoid the shortest and the longest arms. The results support the idea that genes with different properties tend to have different gene territories within the human chromosomes.

Characterisation of a tandem repetitive sequence cloned from the deer Capreolus capreolus and its chromosomal localisation in two muntjac species

The isolation and characterisation of a highly repetitive DNA sequence from the genome of the Roe deer Capreolus capreolus is reported. This sequence is characterised by tandem repetition and located within centric heterochromatin as demonstrated by non isotopic in situ hybridisation to the karyotypes of the Indian and Chinese muntjacs. Amplification and/or clustering of these sequences during the drastic karyotype evolution of the genus Muntiacus was noted in the large centromere of the X chromosome of the Indian muntjac. Partial sequence analysis revealed a 62% sequence homology with the sat 1A sequences of Muntiacus muntjak vaginalis.

Chromosome rearrangements and transposable elements

There has been limited corroboration to date for McClintock's vision of gene regulation by transposable elements (TEs), although her proposition on the origin of species by TE-induced complex chromosome reorganizations in combination with gene mutations, i.e., the involvement of both factors in relatively sudden formations of species in many plant and animal genera, has been more promising. Moreover, resolution is in sight for several seemingly contradictory phenomena such as the endless reshuffling of chromosome structures and gene sequences versus synteny and the constancy of living fossils (or stasis in general). Recent wide-ranging investigations have confirmed and enlarged the number of earlier cases of TE target site selection (hot spots for TE integration), implying preestablished rather than accidental chromosome rearrangements for nonhomologous recombination of host DNA. The possibility of a partly predetermined generation of biodiversity and new species is discussed. The views of several leading transposon experts on the rather abrupt origin of new species have not been synthesized into the macroevolutionary theory of the punctuated equilibrium school of paleontology inferred from thoroughly consistent features of the fossil record.

Telomere length and telomere-centromere relationships?

The quantitative fluorescence in situ hybridization (Q-FISH) technique enables an accurate estimate of individual telomere lengths, a possibility beyond the resolution of conventional techniques. So far, Q-FISH has been used for the estimate of individual telomere lengths in human, mouse and Chinese hamster chromosomes. This analysis revealed large variations in the size of individual telomeres and a specific intra-chromosomal distribution of telomere lengths; telomeres closer to centromeres appear to be shorter than their counterparts more distant from centromeres. This observation suggests that individual telomere length may be affected by centromere position, a possibility consistent with the theory of chromosome field postulated more than 40 years ago by Lima-de-Faria. The link between the theory of chromosome field and the role of telomere-centromere relationships in the regulation of telomere length is discussed in this article.

Conservation of a 31-bp bovine subrepeat in centromeric satellite DNA monomers of Cervus elaphus and other cervid species

A centromeric satellite DNA clone was isolated from the genome of the European red deer (Cervus elaphus hippelaphus) and designated Ce-Pst1. This clone was localized to the centromeric region of all red deer chromosomes with the exception of a single pair of metacentric autosomes and the Y chromosome. DNA sequence analysis of the 806-bp Ce-Pst1 clone showed 73.0-78.9% sequence homology to four previously isolated cervid centromeric satellite DNA clones, suggesting that the Ce-Pst1 clone is yet another member of the major cervid centromeric satellite DNA family. Using a DNA sequence comparison system, internal 31-bp tandem subrepeats were found in the Ce-Pst1 clone as well as in the other previously reported cervid centromeric satellite DNA monomer sequences. A 31-bp consensus sequence was constructed for each cervid monomer clone and shown to be highly homologous to the 31-bp subrepeat consensus sequence found in bovine 1.715 centromeric satellite DNA. The identification of internal subrepeats in the satellite monomers studied could suggest that amplification of an ancestral 31-bp DNA sequence may have contributed to the genesis of major cervid centromeric satellite DNA. The homology between the 31-bp subrepeats found in cervid and bovid centromeric satellite DNAs substantiates the theory that amplification of this 31-bp DNA sequence may have occurred before the evolutionary separation of these two families 20-25 million years ago.

A tandemly repetitive, centromeric DNA sequence from the Canadian woodland caribou (Rangifer tarandus caribou): its conservation and evolution in several deer species

A highly repetitive DNA clone, designated Rt-Pst3, was isolated from the PstI digest of Canadian woodland caribou (Rangifer tarandus caribou; 2n = 70) genomic DNA. It was found to be a 991 bp monomer of a tandemly repeated DNA sequence comprising about 5.7% of the genome and localized to the centromeric regions of all caribou acrocentric autosomes. Southern blot analyses revealed that this caribou satellite DNA sequence was well conserved in the genomes of five other deer species studied. In situ hybridization studies revealed Rt-Pst3-homologous DNA sequences in the centromeric regions of white-tailed deer chromosomes and Asian muntjac chromosomes, as well as at several interstitial chromosome regions in Indian muntjac chromosomes. Comparisons of the Rt-Pst3 DNA sequence to previously identified centromeric satellite DNA fragments from three other deer species revealed considerable DNA sequence similarity. The first ca. 800 bp of the Rt-Pst3 clone was found to share 73.8% similarity to the CCsatI clone of the European roe deer, 64.7% sequence similarity to the C5 DNA clone of the Chinese muntjac, and 64.8% and 65.6% sequence similarity to the 1A and B1 clones of the Indian muntjac, respectively. Moreover, the last 191 bp of the Rt-Pst3 clone was found to share about 60% DNA sequence similarity to the first 191 bp of the same clone. Amplification of one original ca. 800 bp monomer unit, along with the first 191 bp of the following juxtaposed monomer unit could have resulted in the tandemly repeated, 991 bp monomer unit now seen in the caribou genome. It is postulated that the centromeric satellite DNA found in other deer species, having repeat lengths greater than 800 bp, could also have evolved in a similar manner from a more ancestral monomeric unit of ca. 800 bp.