When we cut our fingernails every so often, using a nail clipper, for convenience or in a cosmetic procedure, they grow back. Made of the protein keratin, nails offer us protection from damage. When an infant’s fingertip is amputated, but only the part beyond the last joint, it grows back to its original shape. A 2013 study by Takeo et al. (Nature, 499, 228-232, 2013) found that there are stem cells, which are cells that can develop into different cell types, in the nail bed that don’t only continuously differentiate into cells that go on to form the hard, keratinised nail plate, they also send signals that orchestrate digit regeneration. These cells activate the Wnt signaling pathway, a process that attracts the nerves needed for regeneration.
The lizard is an unwanted guest at our homes. We often try to kill it using a broomstick but often succeed in only hitting its tail. The fugitive soon regenerates its tail, just like the injured fingertip mentioned above. The molecular biology of the process was summarised by Hutchins et al. in 2014 (PLoS ONE 9(8): e105004). More than 300 genes are involved in the response process, and developmental and wound -response pathways are activated to heal the wound and put the tail back.
While wound repair in both animals and plants has traditionally focused on gene-regulated pathways, recent research is shedding light on the critical role of physical cues in developmental plant biology. A study published recently in Current Biology (vol. 35, issue 16, P3851-3868.E7) by Mabel Maria Mathew and Kalika Prasad at IISER Pune highlights an understudied but critical factor in development and regeneration: cell geometry.
The researchers investigated how the root tip organ with tapered shape reclaimed its shape when amputated. They discovered that the existing cells changed their geometry to guide the alignment of rows of new regenerating cells along an inclined path. These inclined rows of cells finally rebuild the tapered shape of the root. In technical terms, this process is called morphogenesis, the biological process that causes an organism to develop its shape and structure. It involves the coordinated growth, division, differentiation, and organisation of cells to form tissues, organs, and even a complete organism.
Experiments described in this study used root tip regeneration in Arabidopsis thaliana of mustard family as an experimental system to demonstrate how changes in cell geometry contribute to and facilitate morphogenesis.
Using advanced microscopy and experimental tools, the team observed that normal cubelike root cells changed their size and shape into rhomboid shapes, where the altered cells divided diagonally, producing triangular prism-like cells. The diagonal divisions redirected the growth of neighbouring cells along a slanted path, collectively recreating the lost tapered tip.
Mathematical and physical analysis done by the group and their collaborators revealed that the actual force behind these changes is internal mechanical tension — a kind of hidden stress guiding cells to change shape and divide strategically.
Thus, while stem cells and genetic pathways have long been central to understanding morphogenesis, this study highlights an equally important but often overlooked aspect: how cells adapt their shape under stress. It shows that cell size and geometry can play a decisive role in guiding morphogenesis during tissue regeneration. These principles may even hold true across other biological systems, pointing to a more universal role for cell physical cues, in particular cell geometry in shaping life.
dbala@lvpei.org
