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Genomes without contact issues

How parental chromosomes are distributed in the cell nucleus

Munich, 02/10/2009

Half mom and half dad: In all of our body cells, we have two complete sets of genes – one inherited from the mother and one from the father. These gene sets, which are organized into chromosomes, largely determine the biological processes in our organism. When, where and how a gene will be active is influenced by so-called epigenetic factors, which regulate the genetic material. In this context, also the three-dimensional arrangement of chromosomes is important, which leads to the question as to whether the genetic material from both parents is arranged spatially separated or blended together in the cell nucleus. A group of LMU researchers lead by Steffen Dietzel, in cooperation with an American colleague, has now shown that the two chromosome sets which mammals inherit from their parents mix in body cells. “This epigenetically interesting result, however, opens up a bunch of new questions,” reports Dietzel. “For example, it is known that maternal and paternal chromosomes in a certain mouse cell type are spatially separated. Why this is the case, and how this is achieved, is still unclear.”

For more than 100 years, researchers have wondered whether the genetic material inherited from mother and father is spatially separated or not in the offspring’s body cells. “This puzzle is almost as old as the discovery of chromosomes itself,” says Dietzel. “For just as long, there has been the suspicion that there is a separation, as was in fact observed later in certain plant hybrids. In the fruit fly, on the other hand, the respective maternal and paternal chromosomes pair with each other – which rules out spatial separation.”

In vertebrates, such as certain mice, a separation of the parental chromosomes has been previously observed just after merging of the gametes, in the very early stages of embryonic development, but this separation is lost at later stages. There have also been hints, however, that certain cell types may retain this condition, or restore it at later stages of development.

Investigation of chromosome sets in adult mammalian cells has so far been precluded by technical difficulties. Paternal and maternal chromosomes are so similar that usually they cannot be distinguished. Mules provided a solution to this problem. These hybrids are bred from a female horse and a male donkey, whose chromosomes can be distinguished with the approach developed by Dietzel’s team.

“We investigated blood cells and, for comparison, connective tissue cells, so called fibroblasts, of the mule,” the biologist reports. “In both of these, we found no evidence of spatial separation. Quite the opposite: Our results clearly show a mixing of the parental genetic material. So we can rule out a separation of chromosomes as a general phenomenon. Results from one human blood cell type, on which certain aspects of chromosome distribution can be investigated, point in the same direction. This result is important for understanding the three-dimensional arrangement of chromosomes in the nucleus and the epigenetic regulation of the genes.”

The project was carried out in the scope of a collaborative research center funded by the German Research Foundation (Deutsche Forschungsgemeinschaft) and focusing on “Molecular Mechanisms of Normal and Malignant Hematopoiesis”. Dietzel’s group also belongs to the “Bioimaging Network Munich”, part of the “LMUinnovativ Process”. (suwe)

“Parental genomes mix in mule and human cell nuclei”,
Claudia Hepperger, Andreas Mayer, Julia Merz, Dirk K. Vanderwall, Steffen Dietzel
Chromosoma, online February 2009. DOI 10.1007/s00412-008-0200-6.

Images are available through the following contact.

PD Dr. Steffen Dietzel
Department Biologie II and Walter-Brendel Zentrum für Experimentelle Medizin, LMU Munich
Tel.: ++49 (0) 89 / 2180 – 76509
Fax: ++49 (0) 89 / 2180 – 9976509

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