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It was long thought that during an embryo's first cell division, one spindle is responsible for segregating the embryo's chromosomes into two cells. EMBL scientists now show that there are actually two spindles, one for each set of parental chromosomes, meaning that the genetic information from each parent is kept apart throughout the first division. Science publishes the results—bound to change biology textbooks—on 12 July 2018.
This dual spindle formation might explain the high error rate in the early developmental stages of mammals, spanning the first few cell divisions. "The aim of this project was to find out why so many mistakes happen in those first divisions," says Jan Ellenberg, the group leader at EMBL who led the project. "We already knew about dual spindle formation in simpler organisms like insects, but we never thought this would be the case in mammals like mice. This finding was a big surprise, showing that you should always be prepared for the unexpected."
Scientists - Chromosomes - Parts - Nucleus - Two-cell
Scientists have always seen parental chromosomes occupying two half-moon-shaped parts in the nucleus of two-cell embryos, but it wasn't clear how this could be explained. "First, we were looking at the motion of parental chromosomes only, and we couldn't make sense of the cause of the separation," says Judith Reichmann, scientist in EMBL's Ellenberg group and first author of the paper. "Only when focusing on the microtubules—the dynamic structures that spindles are made of—could we see the dual spindles for the first time. This allowed us to provide an explanation for this 20-year-old mystery."
What is mitosis?
Mitosis - Process - Cell - Division - Cell
Mitosis is the process of cell division, when one cell splits into two daughter cells. It occurs throughout the lifespan of multi-cellular organisms but is particularly important when the organism grows and develops. The key step of mitosis is to pass an identical copy of the genome...
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