“How many different cell types are generated from a single egg cell?” is one of the most fundamental questions posed by biologists. Now researchers from EMBL Heidelberg and the University of Padua School of Medicine have published in the journal Cell, the first complete description of early embryo development, looking at every cell in the first seven cell divisions of an embryo. This breakthrough research was achieved by constructing a “virtual embryo” of the Phallusia mammillata – a type of marine organism known as a sea squirt, which is found in the Mediterranean Sea and the Atlantic Ocean.

Studying cellular diversification has always been challenging to scientists. Studies, to date, have focused on either researching a limited number of gene markers or by selecting a few cell lineages. This has meant that scientists have not have a good understanding of the gene expression programmes that command individual cells to acquire the cell fates necessary to develop an embryo. Despite recent progress in the field, a comprehensive representation of embryonic development, accounting for every single cell in space and time had not, until now, been achieved.

The construction a ‘virtual embryo’ of Phallusia mammillata, by the EMBL researchers has helped solve this problem. Phallusia mammillata has the advantage of being related to vertebrates and that each specimen has the same number of cells, making it easier for researchers to combine observations.

Digital embyro

The EMBL ‘virtual embryo” described the gene expression and morphology of every cell of an embryo for its first seven cell divisions – from the single cell to the 64-cell stage. This is significant, because, by this point, the fates of the nerve cord, brain, germ cells, blood cell precursors and muscles have all been defined. Descriptions of the gene expression and spatial position of every cell are now possible. This portrayal was achieved through the use of high-resolution single-cell transcriptomics and light-sheet imaging. Click here for 4D digital visualisation of single cell expression patterns (digitalembryo.org). (The 4D visualisation of single-cell expression patterns above. Credit: Hanna Sladitschek/EMBL).

This important breakthrough in developmental genomics will give scientists the ability to track genome-wide changes of gene expression of every cell at each cell division in an embryo. Whilst this research was based on an organism with a small number of cells, the next step would be to extend the work to organisms with a greater number of cells, such as mammals.

For further information:-
Virtual Embryo Allows Single-cell Studies in Unprecedented Detail
Technology Networks

MorphoSeq: Full Single-Cell Transcriptome Dynamics Up to Gastrulation in a Chordate
Authors Hanna L. Sladitschek, Ulla-Maj Fiuza, Dinko Pavlinic, Vladimir Benes,
Lars Hufnagel, Pierre A. Neveu

Gene expression atlas of the Phallusia mammillata early embryo
Digital Embryo

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