Transfer of a human chromosomal vector from a hamster cell line to a mouse embryonic stem cell line.

Two transchromosomic mouse embryonic stem (ES) sublines (ESMClox1.5 and ESMClox2.1) containing a human minichromosome (MC) were established from a sample of hybrid colonies isolated in fusion experiments between a normal diploid mouse ES line and a Chinese hamster ovary line carrying the MC. DNA cytometric and chromosome analyses of ESMClox1.5 and ESMClox2.1 indicated a mouse chromosome complement with a heteroploid constitution in a subtetraploid range; the karyotypes showed various degrees of polysomy for different chromosomes. A single copy of the MC was found in the majority of cells in all the isolated hybrid colonies and was stably maintained in the established sublines for more than 100 cell generations either with or without the selective agent. No significant differences from the ES parental cells were observed in growth characteristics of the transchromosomic ES sublines. ESMClox1.5 cells were unable to grow in soft agar; when cultured in hanging drops, they formed embryoid bodies, and when inoculated in nude mice, they produced teratomas. They were able to express the early development markers Oct4 and Nanog, as demonstrated by reverse transcription-polymerase chain reaction assay. All these features are in common with the ES parental line. Further research using the transchromosomic ES sublines described here may allow gene expression studies on transferred human minichromosomes and could shed light on the relationships among ploidy, pluripotency, cell transformation, and tumorigenesis. Disclosure of potential conflicts of interest is found at the end of this article.

A set of duplicons on human chromosome 9 is involved in the origin of a supernumerary marker chromosome.

Human chromosome 9 is involved in a number of recurrent structural rearrangements; moreover, its pericentromeric region exhibits a remarkable evolutionary plasticity. In this study we present the molecular characterization of a constitutional rearrangement, involving the 9p21.1q13 region, which led to the formation of a supernumerary marker chromosome (SMC). We defined the sequence of the breakpoints and identified a new set of duplicons on human chromosome 9, named LCR9s (chromosome 9 low-copy repeats). Two of these duplicons were shown to be involved in a somatic exchange leading to the formation of the SMC. High-resolution FISH coupled to database search demonstrated that a total number of 35 LCR9 paralogs are present in the human genome. These newly described chromosome 9 duplicons have features that may be crucial in driving structural chromosome rearrangements in germinal and somatic cells.

Isolation from the horse genome of a new DNA transposon belonging to the Tigger family.

Tigger elements are human DNA transposons homologous to the pogo element of Drosophila melanogaster. They contain an open reading frame for a transposase very similar to the major mammalian centromere protein CENP-B. We found in the horse genome a DNA element ( Ecatig3) sharing 88% homology with human Tigger3. The presence of Tigger elements in the horse genome confirms previous data that date these elements before the divergence between Perissodactyla and Primates (80-90 Myr ago). Copy number evaluation indicates that the horse element is much more abundant than its human counterpart. Southern blot analysis demonstrates that Ecatig3 elements are extremely homogeneous; this may indicate that the evolution of this DNA transposon has been driven by some kind of selection and has not been neutral.

Human chromosomes 9, 12, and 15 contain the nucleation sites of stress-induced nuclear bodies.

We previously reported the identification of a novel nuclear compartment detectable in heat-shocked HeLa cells that we termed stress-induced Src-activated during mitosis nuclear body (SNB). This structure is the recruitment center for heat shock factor 1 and for a number of RNA processing factors, among a subset of Serine-Arginine splicing factors. In this article, we show that stress-induced SNBs are detectable in human but not in hamster cells. By means of hamster>human cell hybrids, we have identified three human chromosomes (9, 12, and 15) that are individually able to direct the formation of stress bodies in hamster cells. Similarly to stress-induced SNB, these bodies are sites of accumulation of hnRNP A1-interacting protein and heat shock factor 1, are usually associated to nucleoli, and consist of clusters of perichromatin granules. We show that the p13-q13 region of human chromosome 9 is sufficient to direct the formation of stress bodies in hamster>human cell hybrids. Fluorescence in situ hybridization experiments demonstrate that the pericentromeric heterochromatic q12 band of chromosome 9 and the centromeric regions of chromosomes 12 and 15 colocalize with stress-induced SNBs in human cells. Our data indicate that human chromosomes 9, 12, and 15 contain the nucleation sites of stress bodies in heat-shocked HeLa cells.