How does a tissue know if it is growing at an optimal pace? This is not an easy question to address and can be highly dependent on the specific context. Proper growth rate is essential for normal development and can be regulated at many levels, such as temperature, cell-cell signaling, metabolism and hormones.
Following our earlier discovery of the positive feedback loop coupling multiple tissues of the elongating body axis in avian embryos (Xiong et al., 2020), we now present a hypothesis of elongation speed control by the same interactions but as a negative feedback loop through cell density. In Lu et al., (available on BioRxiv) we combined modeling, mechanical perturbations and cell dynamics analysis to analyze the regulatory logic of elongation centered on the cell density in the posterior presomitic mesoderm. We found that experimentally lengthened and shortened embryos could adjust their elongation speed through changing progenitor influx to the posterior presomitic mesoderm, achieving a fast and robust recovery to normal length. This simple model where cell density relates positively to acceleration but negatively to progress provides a stable elongation speed that works cooperatively with the segmentation clock to produce a stereotypic body plan.
This work includes 3D and 2D agent-based models of the posterior body axis developed by Chris Chan (former PartIII student) and Ala Maksymiuk (former summer student), experimental work altering embryo length via pulling and compression followed by cell density and movement analysis conducted by Dr. Changqing Lu (former visiting scholar) and Joana Vidigueira.