Cell division: Embryos may occur a few hours later than expected

In order to create an embryo, the nuclei of the father and mother must merge into the egg. Now it turns out: this is probably only after the first division.

Cell division: Embryos may occur a few hours later than expected

When exactly does sperm and ovum become an embryo? A new, glaringly life? Until now, it was thought that maternal and paternal nucleus of mammals would merge directly after fertilization. According to a new study, however, two sets of chromosomes remain separated during first cell division. The study of European Molecular Biology Laboratory (EMBL) (Science: Reichmann et al., 2018) could thus redefine time of embryo formation.

Before chromosomes double in cell division, y are separated. For this, y line up with a thread-like structure in cell, a so-called spindle. According to previous view, a single spindle is responsible for separation of all chromosomes of an embryo. However, study published in Science magazine Science shows that re are two spindles in first cell division of mouse embryos, one for a parental set of chromosomes. This double spindle separates genetic information from each or during first cell division. A common nucleus is formed only after that. A video published by EMBL shows process.

The knowledge may also be legally relevant. For some countries, including Germany, as beginning of Schützenswürdigen human life, set merger of parental nuclei after fertilization. If process in humans is similar to that of examined mice embryos, it would be a few hours later than intended for emergence of new life.

Explanation for errors in first cell splits

The newly discovered double spindle could also explain part of high error rate in first cell divides of mammals. Errors in separation of chromosomes may form cells with several cell nuclei, a common reason why an embryo does not evolve. "The goal of this project was to find out why re are so many mistakes in first splits," says Jan Ellenberg, head of project at EMBL. "We already knew that with simpler animals such as insects, two spindles would be formed, but would never have suspected that this is case for mammals like mice as well." In future, it is important to find out wher process is same in humans, says Ellenberg. This could also make progress in research into human infertility.

The results could also solve an old enigma of embryology: parental chromosomes are arranged in round cell nuclei of zweizel embryos to two crescents. So far, re has been no conclusive explanation for this phenomenon. "At first we tracked movements of parental chromosomes, but we could not find a cause for this distribution," says Judith Reichmann, a scientist at EMBL and first author of article. "Only when we focused our attention on microtubules – dynamic structures that make up spindles – we were able to see double spindles for first time."

Of course, results are not entirely new, explains Michael Boiani, head of Working group "mouse Embryology" at Max Planck Institute for Molecular Biomedicine Münster to Science Media Center Deutschland: "It was already shown in year 2005 on Mice (Nature: Plusa et al. ) that chromosomes of maternal and paternal core are not mixed with each or in resulting spindle. " The study now published, however, is a mechanistic explanation with discovery of two spindles.

The discovery was made possible only by a technical innovation developed by EMBL researchers *: Light leaf microscopy. Embryos are very sensitive to light in early stages of development and are damaged by conventional light microscopy methods. Due to new method y are only illuminated very briefly and spatially, so that even hirto hidden processes can be observed.

* Note: In a previous version it was said that EMBL researchers had developed Lichblattmikroskopie. That is not correct. They have only furr developed technology that has been discovered a long time ago. We ask you to apologize for this inaccuracy.

Date Of Update: 14 July 2018, 12:02

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