Instead, Preuss and colleagues have constructed MMCs that contain DNA sequences found in maize centromeres, the chromosomal regions needed for inheritance. Rather than inserting the new genes randomly into a plant's natural chromosomes, these mini-chromosomes remain separate.
As a result, the new genes can be arranged in a defined sequence, with each gene surrounded by the desired regulatory mechanisms. This results in more consistent and controlled expression. The whole cassette of genes is passed on as a group during cell division as well as to the next generation.
In their PLoS paper, the researchers characterized the behavior of the maize mini-chromosome through four generations. Using a gene for red color as a marker, they showed that the added genes are expressed "in nearly every leaf cell, indicating stability through mitosis" -- the process in which a cell duplicates its chromosomes to generate two identical daughter cells.
They also show that the MMC is efficiently passed on through meiosis, the creation of gametes, to the next generation, at ratios "approaching Mendelian inheritance."
Taken together, the authors conclude, the maize mini-chromosome, once introduced, behaves much like an ordinary chromosome. It remains distinct from the other chromosomes. Its gene cassette is structurally stable from generation to generation. The genes it carries are expressed and it is transmitted through mitosis and meiosis.
This development has not gone unnoticed. Six years ago, Preuss and two of her post-doctoral students at the University, Gregory Copenhaver and Kevin Keith, started Chromatin to refine and apply this technology. On Octobe
|Contact: John Easton|
University of Chicago Medical Center