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A work published in the journal 'Science': "Scream or whisper, the dilemma of embryonic cells".

Highlighting the research of Emmanuel Faure of the ICAR team published in the journal Science, also published in CNRSinfo.

“Shouting or whispering: the embryonic cell dilemma.”

During embryonic development, as cells divide, they take on increasingly precise roles in the body. Epidermal cells, muscular or neuronal, the different cell types that make up the embryo gradually emerge from a very fine orchestration of the positions of the cells, coordinated by the signals they exchange between them. Like us, the cells “talk” to each other to make decisions.

In vertebrate embryos, the cells have a very dynamic behavior with numerous migrations and exchanges of neighbors. The signals they exchange, which could be characterized as “screams”, have a long range. The study of the embryonic development of a small marine animal of the ascidian family, whose transparency of embryos facilitates the study, has enabled scientists from several CNRS and INRIA teams in France, in collaboration with a team from the European Molecular Biology Laboratory (EMBL, Germany), to capture and describe in detail another mode of communication.

They recorded every two minutes the development of living embryos with a new generation microscope and then created software to automatically detect each cell and analyze its position, shape and neighbors up to an advanced stage of development. This work revealed a very particular and reproducible mode of development, in which the cells move very little in relation to each other. The authors of the study then annotated the resulting films with information about the cell type and the molecular signals emitted by each cell. By integrating by mathematical modeling the quantitative description of the embryonic geometry with these two new pieces of information, they showed that the signals exchanged by the cells have a very short range. Moreover, the interpretation of these signals is modulated by the surface of the contacts between cells, as if they were whispering instructions to each other, a mechanism facilitated by the small movements of the cells relative to each other. Unlike vertebrates, the cells of ascidian embryos thus have a static and fixed behavior and the range of their “whispered” signals is very small.

This study indicates that the dynamics of cell movements vary greatly between animals and that this could be strongly related to the useful range of signals that cells exchange between themselves. By extending the repertoire of cellular communication mechanisms, this work opens new perspectives on the understanding of self-organization strategies of living forms.

Article : L. Guignard*, U.-M. Fiuza*, B. Leggio, J. Laussu, E. Faure, G. Michelin, K. Biasuz, L. Hufnagel, G. Malandain#, C. Godin#, P. Lemaire# (2020) Contact-area dependent cell communications and the morphological invariance of ascidian embryogenesis (Science, July 10 2020 issue,



© Léo Guignard

Legend of the figure: embryonic development of an ascidian from egg to tadpole. The part framed in white is the part of embryogenesis that we have imaged and then segmented (below, segmented cells coloured according to their cellular fate). The lower part of the figure illustrates that the light green cells “whisper” instructions to their immediate neighbors by short-range signals.