Comparative analysis of karyotypes in European shrew species. I. The sibling species Sorex araneus and S. gemellus: Q-bands, G-bands, and position of NORs

The very long telomeres in Sorex granarius (Soricidae, Eulipothyphla) contain ribosomal DNA

Two closely related shrew species, Sorex granarius and Sorex araneus, in which Robertsonian rearrangements have played a primary role in karyotype evolution, present very distinct telomere length patterns. S. granarius displays hyperlong telomeres specifically associated with the short arms of acrocentrics, whereas telomere lengths in S. araneus are rather short and homogenous. Using a combined approach of chromosome and fibre FISH, modified Q-FISH, 3D-FISH, Ag-NOR staining and TRF analysis, we carried out a comparative analysis of telomeric repeats and rDNA distribution on chromosome ends of Sorex granarius. Our results show that rDNA sequences forming active nuclear organizing regions are interspersed with the long telomere tracts of all short arms of acrocentrics. These observations suggest that the major rearrangements that gave rise to today's karyotype in S. granarius were accompanied by a profound reorganization of chromosome ends, which comprised extensive amplification of telomeric and rDNA repeats on the short arms of acrocentrics and finally contributed to the stabilization of telomeres. This is the first time that such telomeric structures have been observed in any mammalian species.

Chromosome painting comparison of Leontopithecus chrysomelas (Callitrichine, Platyrrhini) with man and its phylogenetic position

Using human probes of whole chromosomes, the homoeologies between human and Leontopithecus chrysomelas (Platyrrhini) karyotypes were established. Thirty-three conserved segments were observed between the two species. Intrachromosomal rearrangements between the two species were identified using hybridization of chromosome arm probes of human chromosomes 1 and 3. We also used chromosomal data to investigate phylogenetic relationships of Callitrichines. These data were encoded using Cebus capucinus , a species which kept fairly ancestral chromosomes, as reference. Two equi-parsimonious trees, including reversion or convergence events, were obtained. The monophyly of Callitrichines is confirmed. They share nine chromosomal rearrangements at least. The Cebuella-Callithrix group forms a clade sharing five rearrangements at least. According to the tree considered, the Tamarins, Leontopithecus and Saguinus share two chromosomal rearrangements restricted to these two taxa or none. Callimico accumulated seven chromosomal rearrangements unshared with other taxa, at least. To avoid convergence and reversion events, we propose the hypothesis of a network (or populational) evolution. Six chromosomal rearrangements would have occurred during the period of this network evolution. Finally, the karyotype of the last common ancestor to all Callitrichines has been reconstructed. It possessed 48 chromosomes.

Karyotypic races of the common shrew (Sorex araneus L.) from northern Poland

Karyotypic races of the common shrew which differed with respect to the combinations of chromosome arms in certain 2-armed autosomes were distinguished in Poland. Two eastern races with the arm combination ik, and one western race with the arm combination hi in the third pair of autosomes were established. In the contact area of these chromosomal forms, the fourth karyotypic race with the arm combination hk was found.

Genome evolution in pocket gophers (genus Thomomys). III. Fluorochrome-revealed heterochromatin heterogeneity

Heterochromatin is a dominant component of the genome in the bottae group of the pocket gopher genus Thomomys, having had a major role in the karyotypic evolution of member species. Heterochromatin characteristics of two subspecies of T. bottae and one of T. umbrinus were examined with fluorochrome dyes identifying presumptive GC- and AT-rich regions. In two karyotype forms of T. b. fulvus and in T. umbrinus, chromatin that fluoresces brightly with chromomycin A3 is also C-band positive, although not all heterochromatin fluoresces. However, in T. b. bottae, only euchromatic regions fluoresce brightly with chromomycin. Fluorescence patterns produced with DAPI are the reverse of the chromomycin banding in all karyotypic forms. Heterochromatin in these taxa is thus highly differentiated, exhibiting heterogeneity in staining characteristics, and presumably in underlying DNA sequences, both across the genome within a given chromosomal complement as well as among the different karyotypic races and species of the bottae group of pocket gophers.

Evolution of the genome size in Akodon (Rodentia, Cricetidae)

Nuclear DNA contents were estimated by microdensitometry in five species of Akodon rodents: Arodon molinae, A. dolores, A. mollis, A. azarae, Bolomys obscurus) and in three chromosomal varieties of A. molinae (2n = 42; 2n = 43, 2n = 22). The data obtained showed that the species with the highest DNA content was B. obscurus, followed in order of decreasing genome size by A. molinae, A. mollis, A. dolores and A. azarae. In A. molinae the forms with 2n = 42 chromosomes had the lowest and the forms with 2n = 44 the highest amount of DNA, while the forms with 2n = 43 had intermediate DNA contents. The variation in DNA amount detected in A. molinae was interpreted as a phenomenon of amplification occurring in the chromosomal areas involved in the chromosomal rearrangement giving rise to the polymorphism exhibited by this species. The DNA contents of shared chromosomes (chromosomes with similar size, morphology and G banding pattern, which are found in two or more phylogenetically related species), were compared and correlated with values of total nuclear DNA. The information obtained indicates that: (a) shared chromosomes have variable amounts of DNA: (b) in a given species there is a correlation between the amount of nuclear and chromosomal DNA in most shared chromosomes (and perhaps in most of the chromosomal complement), e.g., the higher the amount of nuclear DNA, the higher the content of DNA in shared chromosomes; (c) some chromosomes may undergo processes of amplification or deletion restricted to certain regions and usually related with mechanisms of chromosomal rearrangements.(ABSTRACT TRUNCATED AT 250 WORDS)