#fertilisation

Eggsplosion!

One of life’s most delicate processes starts with an explosion. This mouse’s ovarian follicle prepares to launch an egg at high speed – the black circle here (~100 times smaller than a cannonball). Like a lot of dramatic biological events, ovulation is usually hidden from view, so scientists find innovative ways to examine its steps. Bathing this mouse follicle in nurturing chemicals under a microscope, scientists use fluorescent dyes to highlight its membrane (green) and the liquid inside (red). They find that first, the follicle expands, filling up with chemicals rushing in from its surroundings. Fit to burst, muscle cells on the outside squeeze the follicle, which ruptures at a thin part of its wall, propelling the egg on its way. Perhaps starting from a similar blast, the journey from human ovulation to fertilisation to pregnancy is still full of mystery, relying on experiments like these for clues.

Written by John Ankers

Video from work by Christopher Thomas and Tabea Lilian Marx, and colleagues

Max Planck Institute for Multidisciplinary Sciences, Göttingen, Germany

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

Published in Nature Cell Biology, October 2024

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Park Ji-Young collapsed while waiting for 'Liver transformation'

Further Developments

Exposing lab-grown models of early human development called gastruloids to retinoic acid makes them more faithful mimics of embryos that have implanted into the uterus [womb]

Read the published research article here

Image from work by Nobuhiko Hamazaki and Wei Yang, and colleagues

Department of Genome Sciences, University of Washington, Seattle, WA, USA

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

Published in Nature Cell Biology, August 2024

That’ll Do Now

Enzyme called MARC3 blocks further sperm entering eggs within seconds after fertilisation in the model organism C.elegans – insight for fertilisation studies in humans

Read the published research article here

Image from work by Ichiro Kawasaki, Kenta Sugiura and Miyuki Sato, and colleagues

Institute for Molecular and Cellular Regulation, Gunma University, Maebashi, Gunma, Japan

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

Published in Nature Communications, January 2024

The Eggs Factor

Fertilised eggs contain hundreds of molecular ‘protein-building’ instructions called mRNAs. They need to be followed precisely in the right place, at the right time to create embryos. As egg cells, or oocytes, mature, they produce these mRNAs in preparation, but here’s the problem: accumulating these mRNAs before they're needed can hinder development. Quite a conundrum, but researchers have identified a protein that can balance being ready to spring into action with successful embryo development. Nanog is known to amplify mRNA messages in the early embryo. Now researchers have found that it helps silence pre-made mRNAs in eggs and how that impacts development. By injecting a dye (red) into fertilised oocytes, they followed how cells move during normal development (pictured). In oocytes without Nanog, this movement was more sluggish so embryos don’t develop properly. While the full extent of Nanog’s hidden talent needs to be uncovered, it’s clear that it is important for successful development.

Written by Sophie Arthur

Video from work by Mudan He and Shengbo Jiao, and colleagues

State Key Laboratory of Freshwater Ecology and Biotechnology, Institute of Hydrobiology, Innovation Academy for Seed Design, Chinese Academy of Sciences, Wuhan, China

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

Published in Development, December 2022

Placental Invasion

The ability of a fertilised egg to not only create a whole life form, but also the placenta, an organ vital to its survival, is mesmerising. For a successful pregnancy, the placenta has many crucial jobs including invading and attaching to the uterus so nutrients can be passed to the embryo. This is called extravillous trophoblast invasion and is done by cells called extravillous trophoblasts (EVTs). If this isn’t done correctly, it can result in miscarriage, early-onset pre-eclampsia or even foetal growth restriction, but what might be controlling this important step was unclear. Researchers have now revealed that a protein called TGF-β plays a key role. By preventing TGF-β signalling (bottom with and without fluorescent markers), EVTs can form structures called lamellipodia, long spindles that are indicative of cell’s moving. EVTs thus become invasive and able to support placental function. Such detailed understanding of this process may inform future treatments for complications of pregnancy.

Written by Sophie Arthur

Image adapted from work by Sandra Haider and colleagues

Placental Development Group, Reproductive Biology Unit, Department of Obstetrics and Gynaecology, Medical University of Vienna, Vienna, Austria

Image originally published with a Creative Commons Attribution – NonCommercial – NoDerivs (CC BY-NC-ND 4.0)

Published in Proceedings of the National Academy of Science (PNAS), July 2022