In a project that began with the retinal cells of nocturnal animals and has led to fundamental insights into the organization of genomic DNA, researchers from Ludwig-Maximilians-Universitaet (LMU) in Munich show how the nuclear envelope affects nuclear architecture - and gene regulation.
The double-stranded DNA molecules that make up the genetic material are wrapped around protein complexes to form compacted "chromatin". The active portion of the genome is less densely packed, and thus more easily accessible, than the inactive fraction, and is referred to as euchromatin. Euchromatin is typically located in the inner regions of the cell nucleus, while much of the inactive DNA in "heterochromatin" is associated with the inner face of the nuclear envelope. This type of chromatin organization is found in almost all higher organisms and may have been invented 500 million years ago.
But there is a curious exception to this generalization. In the retinal cells of nocturnal animals, the heterochromation is localized in the central area of the nucleus, as a research group led by LMU biologists Dr. Irina Solovei and Dr. Boris Joffe showed in a previous study. "This got us interested in the mechanisms that control the distribution of chromatin," says Professor Heinrich Leonhardt of LMU's Biozentrum. "How can the nuclear architecture in the rod cells of nocturnal animals be inverted in this way, and what determines the typical positioning of inactive chromatin on the outskirts of the nucleus in normal cells?" Leonhardt and his team have now completed an extensive study in search of the answers.
A fundamental principle unveiled
With the help of targeted genetic manipulations in the mouse, Joffe and Solovei together with their colleagues show for the first time that there are two independent mechanisms for fixing heterochromatin to the inner face of the nuclear envelope. These mechanisms make use of two different components of the inner
|Contact: Luise Dirscherl|