Scientists from the University of Tohoku have for the first time provided experimental evidence that cell stickiness helps them stay sorted within the correct compartments during development. Firmly packed cells, known as cell adhesion, appear to allow a protein better known for its role in the immune system. The findings are described in detail in the journal Nature Communications.
Scientists have long noticed that as yet non-specialized cells move in a way that ensures that cell groups destined for a particular tissue stay together. American biologist Malcolm Steinberg proposed in 1964 that cells with similar stickiness move to come into contact with each other to reduce energy consumption, creating a thermodynamically stable structure. This is known as the differential adhesion hypothesis.
“Many other theoretical papers have highlighted the importance of differences in adhesion between cells and cells for separating cell populations and maintaining boundaries between them, but this has not yet been proven in living animal epithelial tissues,” says Erina Kuranaga of Tohoku University Laboratory for Histogenetic Dynamics. led investigations. “Our research showed for the first time that cell sorting is regulated by changes in adhesion.”
Kuranaga and her team conducted experiments in fruit fly pupae, discovering that a gene called Toll-1 played a major role in this adhesion process.
As fruit flies develop from an immature larval stage to a mature adult, epithelial tissue cells called histoblasts accumulate in several ‘nests’ on the abdomen. Each nest contains a front and a back compartment. Histoblasts are intended to replace larval cells to form the adult epidermis, the most distant layer covering flies. The cells in each compartment are made up of discrete cell populations, so they must be held together, creating a clear boundary between them.
Using fluorescent labels, Kuranaga and her team observed that Toll-1 protein is expressed mainly in the posterior compartment. Its fluorescence also showed a sharp boundary between the two compartments.
Further studies showed that Toll-1 performed the function of an adhesive molecule, encouraging similar cells to stick together. This procedure keeps the boundary between the two compartments flat, correcting distortions caused by cell division to increase the number.
Interestingly, toll proteins are best known for recognizing pathogen attacks, and little is known about their work outside the immune system.
Our work improves the understanding of the non-immune role of toll-paying proteins. “
Erina Kuranaga, Laboratory for Histogenetic Dynamics, University of Tohoku
She and her team next plan to study the function of other toll genes in fruit fly epithelial cells.
Iijima, N., and others. (2020) Differential cell adhesion applied by Drosophila Toll corrects local distortions of the anterior and posterior compartment boundaries. Nature Communications. doi.org/10.1038/s41467-020-20118-y.