#blastocyst

Keeping Options Open

Within a few days of fertilisation, the cells of an embryo can take either of two paths; form the embryo itself, or be in the group that becomes the placenta and yolk sac. As a cell journeys further down a particular path, its options become more limited. Usually, it’s particularly difficult to cross between paths, but the early embryo has a group of ‘backup’ cells that for only a small window could join either path and compensate for any changes. We know very little about these intermediate cells, but now researchers have found a way to grow them in the lab. These intermediate cells assemble into ‘artificial blastocysts’, spheres called blastoids (top row enlarging over 4 days, and ‘sliced’ through, bottom row) providing a new way to study in detail this mysterious stage of how embryos' options are kept open for as long as possible.

This study was in collaboration with the MRC London Institute of Medical Sciences' Developmental Epigenomics group

Written by Sophie Arthur

Image adapted from work by Anusha Sathyanarayanan and colleagues

Embryonic Self-Organization Research Group, Max Planck Institute for Molecular Biomedicine, Münster, Germany

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

Published in Science Advances, November 2022

Our day 6/final update is finally here! I slept so terrible last night stressing that none would make it to freeze. The scariest thing about IVF is there is no guarantee. There is a very real possibility that there is no success and another egg retrieval would have to be done right away. And many more thousands of dollars. We officially have two embabies on ice!  We were true to the 40% rate and we are pleased with that. I know Jordan and I are so lucky to have these embryos. I know others have gotten far better results but I also know many have prayed for numbers like ours. Plus, it's quite evident we have a tendency do things in pairs (two dogs, two cats, it's like noah's ark up in here). We have two beautiful chances at a rainbow Also, shoutout to my husband for trying three different places to get me a bag of mini eggs. I wanted to visually represent and celebrate our Easter embryos the only appropriate way!

So we had an anxious wait until today, when we were back in the clinic to see if they had continued to develop, and they had!

Two of the embryos scored the best quality they could on the 3 categories they assess them on. And the other one wasn’t quite as good, but was still good enough that they were happy to use it in future. That means we had one to transfer, and two to freeze, which is so amazing given PCOS eggs are often worse quality!

We went ahead with embryo transfer this afternoon as planned, so now we just have to wait 9 days until we can test! Trying to not get our hopes up, and to remain as stress free as possible for the next week or so.

Here’s our little blastocyst before transfer. We’re calling it our ‘maybe baby’ :)

scribbled womb peeps now, wew

A defining feature of multi-cellular living systems is the capacity to break symmetry and generate well-defined forms and patterns through self-organisation. The Hiiragi group studies early mammalian development at the molecular, cellular and systems levels to elucidate how an intricate embryo emerges from a spherical mass of cells. (source)

Unlocking Early Life

The first few days after sperm meets egg are crucial. One delicate cell division after another leads to a structure called a blastocyst, which will eventually become an embryo. These vital and earliest stages of pregnancy could be considered a well kept secret as they are particularly difficult to study. Shedding more light on them could offer many answers on how to improve in vitro fertilisation (IVF) success rates and the causes of miscarriage. ‘Artificial blastocysts’ called blastoids have already been grown to study early development, but the process of creating them was very inefficient. Researchers have now developed a method for larger scale production. With the new method, more blastoids can be generated with fewer starting resources. But most importantly, they still retain the ability to form embryo-like structures (pictured), with genes key to helping a developing blastocyst penetrate the womb lining switched on (highlighted in pink and cyan), and therefore making them useful for studying implantation.

Written by Sophie Arthur

Image from work by Leqian Yu, Toshihiko Ezashi, Yulei Wei, Jialei Duan and Deirdre Logsdon, and colleagues

Colorado Center for Reproductive Medicine, Lone Tree, CO and Cecil H. and Ida Green Center for Reproductive Biology Sciences, University of Texas Southwestern Medical Center, Dallas, TX, USA

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

Published in bioRxiv, September 2022 (not peer reviewed)

Getting Attached

The blastocyst is a structure that develops around the early embryo before it implants into the wall of the womb. It's essential for implantation and is formed through a series of cell divisions. This involves cell machinery that controls contractility, including proteins such as actin and myosin. Researchers now investigate subunits of myosin called non-muscle myosin II heavy chains (NHMC). Using mouse embryos they created mutants lacking NMHC II-A or NMHC II-B or both. They find NMHC II-A caused major defects in cell division, reduced maturation of cells and other morphological defects in the embryo. NHMC II-B mutants had less severe defects. Double mutants had the most severe defects with cell division failing completely in most cases. However, all mutants were still able to create fluid-filled vacuoles, which is part of the normal process of readying the blastocyst for implantation. This reveals that some events involved in pre-implantation are unaffected by defects in contractility but also that NMHC II-A is the major player in regulating contractility in preparation for implantation.

Written by Lux Fatimathas

Image from work by Markus Frederik Schliffka and Anna Francesca Tortorelli, and colleagues

Genetics and developmental biology unit, Institut Curie, Paris, France

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

Published in eLife, April 2021