Minichromosome

The minimum constituent parts of a chromosome (centromere, telomeres, and DNA replication sequences) are assembled[4] by using molecular cloning techniques to construct the desired chromosomal contents in vitro. Next, the desired contents of the minichromosome must be transformed into a host which is capable of assembling the components (typically yeast or mammalian cells[5]) into a functional chromosome. This approach has been attempted for the introduction of minichromosomes into maize for the possibility of genetic engineering, but success has been limited and questionable.[6] In general, the de novo approach is more difficult than the top-down method due to species incompatibility issues and the heterochromatic nature of centromeric regions.[5]

This method utilizes the mechanism of telomere-mediated chromosomal truncation (TMCT). This process is the generation of truncation by selective transformation of telomeric sequences into a host genome. This insertion causes the generation of more telomeric sequences and eventual truncation.[3] The newly synthesized truncated chromosome can then be altered through the insertion of new genes for desired traits. The top-down approach is generally considered as the more plausible means of generating extra-numerary chromosomes for the use of genetic engineering of plants. In particular it is useful because their stability during cell division has been demonstrated.[7] The limitation of this approach is that it is labor-intensive.

In 2006, scientists demonstrated the successful use of telomere truncation in maize plants to produce minichromosomes that could be utilized as a platform for inserting genes into the plant genome.[10] In plants, the telomere sequence is conserved, which implies that this strategy can be utilized to successfully construct additional minichromosomes in other plant species.[1]

In 2007, scientists reported success in assembling minichromosomes in vitro using the de novo method.[6]

The use of minichromosomes as a means for generating more desirable crop traits is actively being explored. Major advantages include the ability to introduce genetic information which is highly compatible with the host genome. This eliminates the risk of disrupting various important processes such as cell division and gene expression. With continued development, the future for use of minichromosomes may make a huge impact on the productivity of major crops.[11]

Minichromosomes have also been successfully inserted into yeast and animal cells. These minichromosomes were constructed using the de novo approach.[3]