#mesoderm

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Embryonic Choreography

The transformation of an embryo into a baby involves the staggeringly complex choreography of billions of cells. In the opening scenes of this show, three layers of cells must form in an embryo: the endoderm, mesoderm and ectoderm. Researchers now probe how the endoderm, which goes on to form your stomach, intestines, lungs, liver and pancreas, comes to be. Using two-photon, time-lapse microscopy of spheres of mouse embryonic stem cells called gastruloids (pictured), they tracked all cells by labelling them with a dye (left). By fluorescently tagging different proteins, they found some cells lost a protein called E-cadherin while others retained it. Next, islands of cells with E-cadherin were surrounded by cells containing a mesoderm marker, T-Brachyury (middle), and flowed towards one end of the elongating sphere before finally maturing into endoderm cells. This sheds light on some of the earliest moves in the complicated dance of development.

Written by Lux Fatimathas

Video from work by Ali Hashmi and colleagues

Aix-Marseille University, CNRS, IBDM, Turing Center for Living Systems, Marseille, France

Video originally published with a Creative Commons Attribution 4.0 International (CC BY 4.0)

Published in eLife, April 2022

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Histology Glossary: Intramembranous Ossification

**Steps of Intramembranous Ossification** * Embryologically, skeletal tissues typically derive from mesoderm: the midline (axial) skeleton derives from the somites and the appendicular (the limb) skeleton derives from the lateral plate. * Mesen

Here’s one of our Flashcards that explain Intramembranous Ossification!

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Bio Word of the Day:

Coelom

The body cavity;  Located between the body wall and the intestine, and lined with epithelium derived from mesoderm;  Present in metazoans

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Projected Growth

The protective environment of the womb supports growth from just a few cells to a human child. But it also shields those cells from the prying eyes of scientists, for whom practical and ethical limitations prevent the detailed experimentation needed to unpick the secrets of early life. Instead, researchers have tried to recreate the cells and conditions in the lab, but like copying a great work of art, replicating the subtle magic and complexity is tricky. A new study has generated a particular cell, the extraembryonic mesoderm cell, from human stem cells (precursors able to develop into any embryonic cell). In embryos these cells generate blood, help link to the placenta, and form the early umbilical tube. The new creations (pictured, red, with placental cells in green) closely replicate their natural counterparts, and may help shed light on hidden moments of growth, ultimately improving our understanding of fertility and its complications.

Written by Anthony Lewis

Image from work by Thi Xuan Ai Pham and Amitesh Panda and colleagues

Department of Development and Regeneration, Leuven Stem Cell Institute, Leuven Institute for Single-cell Omics (LISCO), KU Leuven-University of Leuven, Leuven, Belgium

Image copyright held by Amitesh Panda (KU Leuven)

Research published in Cell Stem Cell, September 2022

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Shaping Up Differently

In the earliest days of development, gastrulation separates embryonic cells into distinct layers destined to become different tissues and organs. Watching this early mouse embryo under a high-powered microscope, scientists study how the endoderm layer (highlighted in green) develops separately from the mesoderm (red). They know the mesoderm forms when epithelial cells lining the embryo reprogram themselves, switching on specific genes in a process called epithelial–mesenchymal transition. Textbooks have it that something similar happens to the endoderm. Challenging this, the scientists find that some epithelial cells can change their shape – their morphology – then migrate to become part of the endoderm, while making molecules to stop themselves from becoming part of the mesoderm. This discovery may reveal ways to help embryos during development, or perhaps block similar shapeshifting employed by migrating cancer cells.

Written by John Ankers

Image from work by Katharina Scheibner, Silvia Schirge and Ingo Burtscher, and colleagues

Institute of Diabetes and Regeneration Research, Helmholtz Diabetes Center, Helmholtz Zentrum München, Munich, Germany

Image copyright held by the original authors

Research published in Nature Cell Biology, July 2020

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Feeling a Pulse

Stem cells need some direction during gastrulation – the process that sees them grow into different tissues inside an embryo. Proteins called morphogens send guiding signals deep into each stem cell’s nucleus, where lifelong decisions are made. In this cluster of human embryonic stem cells – a sort of artificial early embryo – scientists watch for responses to morphogen molecules. While some early changes happen around the perimeter (highlighted in red), a signal called Nodal spreads inwards (green), leading some cells (blue) to begin changing, or differentiating, into the mesoderm, where muscles form in real embryos. Watching these living ‘models’ reveals that Nodal responds to rhythmic waves of chemical 'messages' – a sort of developmental pulse that may help to understand, or even assist, decisions made at the earliest stages of life.

Written by John Ankers

Image from work by Idse Heemskerk and colleagues

Department of Biosciences, Rice University, Houston, TX, USA

Image originally published under a Creative Commons Licence (BY 4.0)

Published in eLife, March 2019

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Following Fate

You may be the master of your own fate, but for your cells, destiny is predetermined. In the first stages of life, the embryo morphs from a blob of similar cells to increasingly distinct groups. One such group, known as neuromesodermal progenitors, ultimately forms the spinal cord and the paraxial mesoderm – crucial tissue along the midline of the embryo. Understanding this transformation is important, since small errors at this stage can be fatal to human development, so researchers observe the process in animals for comparison. Recent evidence had suggested significant differences between zebrafish and mice (two classic model animals), so the team tracked the precise movement of different cell groups in a zebrafish embryo (one such observation pictured). Mapping the fate of particular cells showed that although their trajectories are alike across species, the intricate timing of their behaviour varies – an important consideration when extrapolating findings from animal experiments to humans.

Written by Anthony Lewis

Video from work by Andrea Attardi and Timothy Fulton, and colleagues

Department of Genetics, University of Cambridge, Cambridge, UK

Video originally published under a Creative Commons Licence (BY 4.0)

Published in Development, November 2018

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