Polar Bearings

We’re often taught that mitosis, a form of cell division, is symmetrical: daughter cells are the same as each other, and their parent cell aren’t they? Well, there are some exceptions. In these early embryonic cells (from a mouse), researchers find some cells get their bearings earlier than others. Early in the timeline on the top row, some cells reveal a glowing part of their cell membrane – a fluorescent stain highlighting a sort of compass needle for the cell (although ~1000 times smaller). Most cells eventually become ‘polarised’ – finding their inner compasses. But researchers following these early polar pioneers find they go on to develop into a distinct part of the embryo called the outer trophectoderm. Investigating asymmetry in early development will help researchers understand how the embryo defines different tissues and organs in mice and humans alike.

Image made using Leica Microsystems microscopy

Written by John Ankers

John Ankers

Writer

A former researcher in systems biology, John is now an online biology tutor and professional coach supporting the wellbeing of scientists and NHS professionals. He's writing, too, of course.

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• Image from work by Adiyant Lamba and Meng Zhu, and colleagues
• Mammalian Embryo and Stem Cell Group, Department of Physiology, Development and Neuroscience, University of Cambridge, Cambridge, UK
• Image originally published with a Creative Commons Attribution 4.0 International (CC BY 4.0)
• Published in eLife (reviewed preprint), August 2025