This video shows the dynamics of dorsal closure in an embryo expressing the caspase marker Apoliner5. At the onset of the process, the GFP fluorescent signal is transferred from the cytoplasm to the nucleus indicating the activation of caspases and apoptosis. At that moment, cells will start to shrink and to pull on the epidermis. The process takes approximately 2h 30min. [Laure Saias, CRG]
Understanding the contractile mechanisms of epithelial cells during embryogenesis is not only an important basic developmental biology concept, as cells and tissues must generate forces for proper development and the shaping of organs, it also has critical implications for wound healing.
Researchers at the Centre for Genomic Regulation (CRG) in Barcelona have released data from a new study describing a mechanism that shapes cells and generates contractile forces during development and organogenesis. The investigators were particularly focused on the dorsal closure of developing Drosophila embryos—a heavily studied area of developmental biology due to its many similarities with wound healing in mammals.
Dorsal closure is a developmental process by which embryonic skin cells are stretched over a gap in order to close it. The edges of the gap form a zipper that pulls the skin cells of the embryo together, thereby shaping them and leading them into the next development stage.
“Mechanisms shaping cells and tissues described until now are based on forces generated by the remodelling of the cell cytoskeletal meshwork and structures that pull, push, or shrink cells. What we have now described is that cells can also generate forces simply by modulating their volume,” explained Jérôme Solon, Ph.D., group leader of Biomechanics of Morphogenesis at the CRG in Barcelona and senior author on the current study.
The findings from this study were published recently in Developmental Cell through an article entitled “Decrease in Cell Volume Generates Contractile Forces Driving Dorsal Closure.”
Dr. Solon and his colleagues took quantitative measurements of the dorsal closure and built a 3D model to improve their understanding of mechanisms that were taking place at a single cell level.
“Surprisingly, we found that cells were not elongating or changing their shape in the manner that was previously thought, but that the cells were actually changing their volume and shrinking,” stated Dr. Solon.
Interestingly, the researchers found that contrary to most of the mechanisms underlying tissue contraction during development, where cells can typically be observed to turn flat and pear-like when changing their shape, they noticed cells that retained their thickness, but decreased their volume, getting much smaller.
“The most curious thing is that the mechanisms driving these volume changes are the same as those that have been found during programmed cell death or apoptosis,” Dr. Solon said. “So, it is important for us to highlight the dual role of apoptosis in this particular developmental process. We feel that these mechanisms are likely to play important roles in other morphogenetic processes shaping tissues and organs, such as wound healing and limb or brain development.”