Cell size and ploidy: from single cells to the physiology of vertebrate embryos

Speaker: Clotilde Cadart, Institut Cochin, Paris, France

Genome copy increase (i.e. polyploidization) correlates cell size increase and is frequent in development, cancer, and throughout evolution. However, the ways ploidy and cell size impact cellular functions and animal physiology remain poorly understood.
To make progress, we are combining quantitative approaches in single-cells and Xenopus embryos. We generated triploid embryos and showed that triploid tadpoles are made of fewer, larger cells than diploids and consume oxygen at a lower rate. To understand the underlying basis of such decrease, we developed a mathematical framework to quantify the energy budget of tadpoles and combined it with quantitative measurements of the energy allocated to proliferation, growth, and maintenance. Results suggest that the increase in cell size in triploids causes a decrease in total cell surface area and a reduction of costs associated with activity at the plasma membrane which explains the overall lower metabolic rate. Crucially, comparison of three Xenopus species that evolved through polyploidization reveals that metabolic differences emerge in development only once cell size scales with genome size.
Ongoing efforts are focusing on understanding how cellular energetics vary with ploidy/cell size at the singlecell level and translate across scales to affect animal physiology across frog species.