J.A. Marshall Graves

Conservation genetics of the koala (Phascolarctos cinereus) II. Limited variability in minisatellite DNA sequences

We have examined variability inTaqI andEcoRI restriction fragment sizes of DNA from the koala (Phascolarctos cinereus) using six HVR (hypervariable region) probes which reveal complex, individual-specific restriction patterns in humans and other species. Frequency of band-sharing among unrelated koalas was extremely high. This result is likely to be a consequence of the history of near-extinction and artificial recolonization of the populations we have studied, rather than a general marsupial or koala-wide phenomenon.

Localization of four human chromosome 21 genes--SOD1, ETS2, IFNAR, and CBR--to two different chromosomes in the marsupial species Macropus eugenii.

We have mapped the chromosomal location of four genes previously assigned to human chromosome 21--Cu/Zn superoxide dismutase (SOD1), the protooncogene ETS2, the interferon alpha/beta receptor gene (IFNAR), and the carbonyl reductase gene (CBR)--in the tammar, Macropus eugenii. The genes are localized on two separate autosomes: SOD1 and CBR map to chromosome 7 and ETS2 and IFNAR map to chromosome 3 or 4. These results provide the first example of asynteny between SOD1/CBR and ETS2/IFNAR in a mammalian species. The results suggest that either this synteny group has been disrupted in the marsupial lineage, or, alternatively, the genes located on human chromosome 21 may have been joined after the marsupials diverged from the eutherian mammals some 130-150 million years ago.

Genome Instability in interspecific cell hybrids II. Aminopterin resistance and gene amplification in lines arising from fusions of cells from divergent mammalian species

In order to investigate instances of genetic instability in divergent cell hybrids, we studied several RAT-resistant colonies recovered from fusions between HPRT or TK-deficient rodent cells and marsupial or monotreme cells. Most of these colonies proved to lack HPRT or TK activity and to have survived by acquiring resistance to aminopterin; such aminopterin-resistant lines were never recovered from parent cells subjected to HAT selection. Two of the aminopterin-resistant hybrids over-produced DHFR, and possessed either double minutes or an abnormally banded region, the cytological manifestations of gene amplification. Selection in higher aminopterin concentrations yielded a highly resistant line with 100X wild-type DHFR activity and a large homogeneously staining region. We suggest that interspecific cell hybrids are predisposed to gene amplification and may also show many other types of genetic and chromosomal instability, possibly thein vitro equivalent of the “genomic shock” phenomena described for interstrain or interspecies hybrids of plants or animals.

Contents Vol. 127, 2009

Jacqueline Smith Division of Genetics and Genomics Roslin Institute, Roslin Midlothian EH25 9PS (UK) Tel. (+44) 131 527 4200 Fax (+44) 131 440 0434 E-mail: jacqueline.smith@bbsrc.ac.uk Plant cytogenetics and genomics Bernd Friebe Department of Plant Pathology Th rockmorton Plant Sciences Center Kansas State University Manhattan, KS 66506-5502 (USA) Tel. (+1) 785 532 2364; Fax (+1) 785 532 5692 E-mail: friebe@ksu.edu