Self-organised symmetry breaking in zebrafish reveals feedback from morphogenesis to pattern formation

Vikas Trivedi, Timothy Fulton, Andrea Attardi, Kerim Anlas, Chaitanya Dingare, Alfonso Martinez-Arias, Benjamin Steventon

Posted on: 7 October 2019

Preprint posted on 18 September 2019

Pescoids - a new in vitro model system to study early zebrafish embryogenesis

Selected by Sundar Naganathan

Categories: developmental biology


Morphogenesis is the process by which groups of cells transform in to tissues of diverse shapes and forms through a complex interplay between gene expression patterns and mechanical processes. To understand morphogenesis, several model systems have been successfully used to document and characterize gene expression patterns spatiotemporally. Yet we are still a long way from understanding the mechanisms by which intricate patterns emerge in embryos in a robust manner. Do early embryos have an intrinsic ability to self-organize? If yes, what are the principles of this self-organization process? Are extra-embryonic tissues, such as the yolk syncytial layer in zebrafish embryos and trophectoderm in mouse embryos important in regulating spatiotemporal gene expression patterning?

Several reports have established that extra-embryonic tissues do play a role in driving morphogenetic events such as mesodermal induction and epiboly in zebrafish1 and anteroposterior and dorsoventral axes establishment in mouse embryos2. However, the advent of the gastruloid model system3, which emerges from mouse embryonic stem cells, has provided an alternative view of early symmetry breaking, where many morphogenetic events such as elongation and anteroposterior patterning emerge in the absence of extra-embryonic tissues. The authors of this preprint further stimulate this debate, by developing a gastruloid-like primary culture system using zebrafish early embryonic cells.

Key observations

The authors explanted zebrafish embryonic cells from the 256-cell stage (~2.5 hrs post fertilization) and characterized emergent morphogenesis in the explants. The explanted cells aggregated and underwent rapid rounds of cell division before elongating from one end. More than 60% of the explants exhibited this polarization suggesting that symmetry breaking can occur spontaneously in embryonic cells in the absence of signals emanating from the yolk. Interestingly, symmetry breaking was observed even when explanted cells were dissociated and re-aggregated. This experiment, in addition to the observation of homogeneous cell mixing upon explantation, suggests that symmetry breaking is likely to be an intrinsic ability of early embryonic cells and is independent of pre-patterns preserved from the embryo.

The self-organized cell aggregates were named pescoids, which exhibited the following spatial gene expression patterns, in addition to the morphological symmetry breaking event:

  1. Mesodermal marker expression in the elongating end;
  2. High BMP activity in a region opposite to the elongating end;
  3. Inhibitors of BMP signalling in the elongating end;
  4. Spatially distinct expression of anteroposterior neural patterning genes, with the posterior genes closer to the elongating end

In vivo, the yolk plays a major role in breaking initial symmetries in the embryo. Do vegetal cells then, which are spatially closer to the yolk, display an enhanced ability to self-organize in explants? To test this, the authors explanted animal and vegetal cells separately and observed that both explants were equally capable of exhibiting elongation. However, the elongation length was smaller than that observed in pescoids suggesting that both animal and vegetal regions are necessary for elongation. Interestingly, when the sizes of the animal and vegetal explants were increased by increasing the starting number of cells, the ability to elongate increased. This suggests that tissue size and large-scale mechanics of the entire aggregate could play a role in determining elongation.

What regulates elongation in the pescoids? The authors observed that spatially localized Nodal signalling precedes mesodermal marker expression and elongation, both of which were abolished upon inhibition of nodal signalling. These observations agree well with recent work where in-depth characterization of Nodal signalling during convergence extension was performed4. Furthermore, inhibition of the planar cell polarity pathway, a major regulator of convergence-extension movements in vivo, also blocked pescoid elongation and severely affected anteroposterior patterning. This suggests that a combination of self-organized Nodal signalling and convergence-extension movements drive pescoid elongation and patterning.

Why I chose this preprint?

The authors have established a new in vitro model system for analysis of early zebrafish embryo morphogenesis. This enables quantitative comparisons to analysis performed in intact embryos providing important information on the role of extra-embryonic tissues in regulating morphogenesis. Furthermore, any in vitro system brings with it an advantage of performing controlled perturbations and pescoids is no different in this respect.

The study has uncovered that early embryonic cells have an intrinsic ability to break symmetry and this discovery is likely to spur in-depth quantitative analysis of symmetry breaking processes and downstream self-organization of spatial gene expression patterns, which are not well understood in vertebrate model systems.

Open questions

  1. The same culture dish seems to have many pescoids at the same time. If a pescoid is cultured in isolation, do the authors expect any change in the quantified parameters? In other words, do pescoids influence each other through long-range signalling?
  2. 3% FBS has been used to culture the pescoids. FBS has a range of different growth factors such as FGF and TGF-b1, which may affect the observed morphogenesis. It is therefore tricky to interpret the observed dynamics and necessitates further control experiments to test the impact of FBS on pescoid morphogenesis.
  3. Even with an aggregate size similar to that of the pescoids, a similar elongation length was not observed in the animal and vegetal explants. This argues that aggregate size may not be the major determining factor in pescoid elongation in contrast to the interpretation in the preprint. Further experiments are required to clearly understand the importance of tissue size in regulating elongation.
  4. In Fig. 3c left image, it appears that the orientation of cell divisions in the periphery of the pescoid seem to align with local curvature of the pescoid. Could the authors test if the material properties of the pescoid in the periphery are different from the interior, where cell division orientations seem to be more random?
  5. Any ideas on why explants generated from embryos that are younger than the 256-cell stage fail to elongate efficiently?


  1. Carvalho L. and Heisenberg C. P., The yolk syncytial layer in early zebrafish development, Trends Cell Biol., 2010
  2. Rivera-Péréz J. A. and Hadjantonakis A-K., The dynamics of morphogenesis in the early mouse embryo, Cold Spr. Har. Persp. Biol., 2015
  3. van den Brink S. C. et al., Symmetry breaking, germ layer specification and axial organisation in aggregates of mouse embryonic stem cells, Dev., 2014
  4. Williams M. L. K. and Solnica-Krezel L., A mesoderm-independent role for Nodal signaling in convergence & extension gastrulation movements, bioRxiv, 2019

Tags: convergence extension, pattern formation, symmetry breaking


Read preprint (No Ratings Yet)

Author's response

Benjamin Steventon shared

  1. We have not done this specifically, although we could note that we culture in large volumes (and that this is important for their survival), this suggests that any secreted signals would rapidly diffuse in the medium.
  2. Fig. S5 and S6 in the Supp Info show that with a varying degree of media composition (L15, DMEM, PBS) and FBS % (1%, 3%, 10%), all conditions allow elongation.
  3. The animal and vegetal explants are always smaller than complete pescoids, so this doesn’t rule out a role for explant size being important. However, it would indeed be interesting to do more animal cap fusion experiments to further confirm the importance of aggregate size. In particular, the effect of having extra tissue has not be fully explored.
  4. It is certainly true that the outer part of the explant takes on different gene expression from the inside, in particular Krt8 expression. Exactly when and how inner vs. outer layers formed will be an important thing to explore in the future.
  5. Most likely this is due to the proper aggregation of the cells. The reason could also be due to the fact that till 32 cell stage, all cells are contiguous with the yolk, so we cannot make explants at this stage. As division starts we get more cells to make explants but the error in manually removing cells with eyelash tool is higher at earlier stages (64-stage and 128-stage) as compared to later stages. So it is likely that we start with less number of cells (critical number) if we harvest them from earlier embryos.


Have your say

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.

Sign up to customise the site to your preferences and to receive alerts

Register here

Also in the developmental biology category:

Gestational exposure to high heat-humidity conditions impairs mouse embryonic development

Avinchal Manhas, Amritesh Sarkar, Srimonta Gayen

Selected by 08 July 2024

Girish Kale, preLights peer support

Developmental Biology

Modular control of time and space during vertebrate axis segmentation

Ali Seleit, Ian Brettell, Tomas Fitzgerald, et al.


Natural genetic variation quantitatively regulates heart rate and dimension

Jakob Gierten, Bettina Welz, Tomas Fitzgerald, et al.

Selected by 24 June 2024

Girish Kale, Jennifer Ann Black

Developmental Biology

Notch3 is a genetic modifier of NODAL signalling for patterning asymmetry during mouse heart looping

Tobias Holm Bønnelykke, Marie-Amandine Chabry, Emeline Perthame, et al.

Selected by 06 June 2024

Bhaval Parmar

Developmental Biology

preLists in the developmental biology category:

BSDB/GenSoc Spring Meeting 2024

A list of preprints highlighted at the British Society for Developmental Biology and Genetics Society joint Spring meeting 2024 at Warwick, UK.


List by Joyce Yu, Katherine Brown

GfE/ DSDB meeting 2024

This preList highlights the preprints discussed at the 2024 joint German and Dutch developmental biology societies meeting that took place in March 2024 in Osnabrück, Germany.


List by Joyce Yu

‘In preprints’ from Development 2022-2023

A list of the preprints featured in Development's 'In preprints' articles between 2022-2023


List by Alex Eve, Katherine Brown

preLights peer support – preprints of interest

This is a preprint repository to organise the preprints and preLights covered through the 'preLights peer support' initiative.


List by preLights peer support

The Society for Developmental Biology 82nd Annual Meeting

This preList is made up of the preprints discussed during the Society for Developmental Biology 82nd Annual Meeting that took place in Chicago in July 2023.


List by Joyce Yu, Katherine Brown

CSHL 87th Symposium: Stem Cells

Preprints mentioned by speakers at the #CSHLsymp23


List by Alex Eve

Journal of Cell Science meeting ‘Imaging Cell Dynamics’

This preList highlights the preprints discussed at the JCS meeting 'Imaging Cell Dynamics'. The meeting was held from 14 - 17 May 2023 in Lisbon, Portugal and was organised by Erika Holzbaur, Jennifer Lippincott-Schwartz, Rob Parton and Michael Way.


List by Helen Zenner

9th International Symposium on the Biology of Vertebrate Sex Determination

This preList contains preprints discussed during the 9th International Symposium on the Biology of Vertebrate Sex Determination. This conference was held in Kona, Hawaii from April 17th to 21st 2023.


List by Martin Estermann

Alumni picks – preLights 5th Birthday

This preList contains preprints that were picked and highlighted by preLights Alumni - an initiative that was set up to mark preLights 5th birthday. More entries will follow throughout February and March 2023.


List by Sergio Menchero et al.

CellBio 2022 – An ASCB/EMBO Meeting

This preLists features preprints that were discussed and presented during the CellBio 2022 meeting in Washington, DC in December 2022.


List by Nadja Hümpfer et al.

2nd Conference of the Visegrád Group Society for Developmental Biology

Preprints from the 2nd Conference of the Visegrád Group Society for Developmental Biology (2-5 September, 2021, Szeged, Hungary)


List by Nándor Lipták


The advances in fibroblast biology preList explores the recent discoveries and preprints of the fibroblast world. Get ready to immerse yourself with this list created for fibroblasts aficionados and lovers, and beyond. Here, my goal is to include preprints of fibroblast biology, heterogeneity, fate, extracellular matrix, behavior, topography, single-cell atlases, spatial transcriptomics, and their matrix!


List by Osvaldo Contreras

EMBL Synthetic Morphogenesis: From Gene Circuits to Tissue Architecture (2021)

A list of preprints mentioned at the #EESmorphoG virtual meeting in 2021.


List by Alex Eve

EMBL Conference: From functional genomics to systems biology

Preprints presented at the virtual EMBL conference "from functional genomics and systems biology", 16-19 November 2020


List by Jesus Victorino

Single Cell Biology 2020

A list of preprints mentioned at the Wellcome Genome Campus Single Cell Biology 2020 meeting.


List by Alex Eve

Society for Developmental Biology 79th Annual Meeting

Preprints at SDB 2020


List by Irepan Salvador-Martinez, Martin Estermann

FENS 2020

A collection of preprints presented during the virtual meeting of the Federation of European Neuroscience Societies (FENS) in 2020


List by Ana Dorrego-Rivas

Planar Cell Polarity – PCP

This preList contains preprints about the latest findings on Planar Cell Polarity (PCP) in various model organisms at the molecular, cellular and tissue levels.


List by Ana Dorrego-Rivas

Cell Polarity

Recent research from the field of cell polarity is summarized in this list of preprints. It comprises of studies focusing on various forms of cell polarity ranging from epithelial polarity, planar cell polarity to front-to-rear polarity.


List by Yamini Ravichandran

TAGC 2020

Preprints recently presented at the virtual Allied Genetics Conference, April 22-26, 2020. #TAGC20


List by Maiko Kitaoka et al.

3D Gastruloids

A curated list of preprints related to Gastruloids (in vitro models of early development obtained by 3D aggregation of embryonic cells). Updated until July 2021.


List by Paul Gerald L. Sanchez and Stefano Vianello

ASCB EMBO Annual Meeting 2019

A collection of preprints presented at the 2019 ASCB EMBO Meeting in Washington, DC (December 7-11)


List by Madhuja Samaddar et al.

EDBC Alicante 2019

Preprints presented at the European Developmental Biology Congress (EDBC) in Alicante, October 23-26 2019.


List by Sergio Menchero et al.

EMBL Seeing is Believing – Imaging the Molecular Processes of Life

Preprints discussed at the 2019 edition of Seeing is Believing, at EMBL Heidelberg from the 9th-12th October 2019


List by Dey Lab

SDB 78th Annual Meeting 2019

A curation of the preprints presented at the SDB meeting in Boston, July 26-30 2019. The preList will be updated throughout the duration of the meeting.


List by Alex Eve

Lung Disease and Regeneration

This preprint list compiles highlights from the field of lung biology.


List by Rob Hynds

Young Embryologist Network Conference 2019

Preprints presented at the Young Embryologist Network 2019 conference, 13 May, The Francis Crick Institute, London


List by Alex Eve

Pattern formation during development

The aim of this preList is to integrate results about the mechanisms that govern patterning during development, from genes implicated in the processes to theoritical models of pattern formation in nature.


List by Alexa Sadier

BSCB/BSDB Annual Meeting 2019

Preprints presented at the BSCB/BSDB Annual Meeting 2019


List by Dey Lab

Zebrafish immunology

A compilation of cutting-edge research that uses the zebrafish as a model system to elucidate novel immunological mechanisms in health and disease.


List by Shikha Nayar