Abstract
The developing zebrafish embryo has been the subject of many studies of regional patterning, stereotypical cell movements and changes in cell shape. To better study the morphological features of cells during gastrulation, we generated mosaic embryos expressing membrane attached Dendra2 to highlight cellular boundaries. We find that intercellular bridges join a significant fraction of epiblast cells in the zebrafish embryo, reaching several cell diameters in length and spanning across different regions of the developing embryos. These intercellular bridges are distinct from the cellular protrusions previously reported as extending from hypoblast cells (1–2 cellular diameters in length) or epiblast cells (which were shorter). Most of the intercellular bridges were formed at pre-gastrula stages by the daughters of a dividing cell maintaining a membrane tether as they move apart after mitosis. These intercellular bridges persist during gastrulation and can mediate the transfer of proteins between distant cells. These findings reveal a surprising feature of the cellular landscape in zebrafish embryos and open new possibilities for cell-cell communication during gastrulation, with implications for modeling, cellular mechanics, and morphogenetic signaling.
Highlights
At gastrula stages, zebrafish embryos have a simple organization, comprised of a few cellular layers and a relatively simple cell morphology
Further imaging revealed that these protrusions were not filopodia; instead, they seemed to be intercellular bridges linking distant pairs of cells
To rule out the possibility that these protrusions were an artifact of the expression of mDendra2, we imaged un-injected embryos at the same stage of development using differential interference contrast (DIC) light microscopy, and confirmed the presence of the previously undescribed intercellular bridges (Figure 1E)
Summary
Zebrafish embryos have a simple organization, comprised of a few cellular layers and a relatively simple cell morphology. Past efforts have been mainly concentrated on the cells in the hypoblast, where blebs, filopodia and pseudopodia are notable features [1,4,5]. These cellular protrusions seem to lead the progressing hypoblast cells down the correct path of migration through the embryo [5]. Epiblast cells are less motile with simpler morphology and with less dynamic protrusions [5,6]
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