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Max F. Perutz Laboratories: key mechanisms in germ cells explained

(Vienna, 05th August 2011) During the development of germ cells in humans, sperm and ova, chromosomes are often broken and then spliced back together. A team of researchers led by Franz Klein, Professor of Genetics at the Max F. Perutz Laboratories at the Medical University of Vienna, has now investigated this process using state-of-the-art technology able to reveal detail in the nanometre range. The surprising results from the mechanisms of meiosis have been published in the latest edition of the renowned specialist journal "Cell".

A little bit of background: there is no sexual reproduction without meiosis, since germ cells are only formed by this special form of cell division. In this process, a cell divides so that daughter cells are produced with single sets of chromosomes instead of the usual double set. If a sperm fuses with an egg cell during fertilisation, the result is an embryo. Its cells then have the double set of chromosomes. Every human cell contains 46 chromosomes, 23 of which come from the mother and 23 from the father. When germ cells are produced, this number is halved by a single daughter chromosome being formed from one maternal and one paternal chromosome, a process known as recombination.

“Meiosis is a puzzling process. It’s incredible that paternal and maternal chromosomes meet each other at all”, explained Klein from the Department of Chromosome Biology at the University of Vienna on Friday in a broadcast. Only the meeting of parental chromosomes guarantees that the resulting germ cells contain the right number of chromosomes. Klein and his team have investigated this tiny, DNA-breaking protein machine that triggers this recombination process. To help them do this, they drew up a high-resolution map of the chromosomes and marked the “landing places” of these proteins. “Thanks to ‘DNA microchip technology’, we are able to achieve a resolution in the nanometre range, giving us completely new perspectives", said the scientist.

The researchers have learned, for example, that the DNA-breaking complexes required for the recombination of chromosomes do not float around from chromosome to chromosome like other “protein machines”, but instead are anchored in the chromosomes themselves. This in turn ensures that breaks only occur at the right place. Once this is done, the mechanisms cease to function. Moreover, the results of the research also show that there needs to be very precise localisation of the proteins that separate the chromosomal substance during meiosis.