Self-organized tissue mechanics underlie embryonic regulation

Early amniote development is a highly regulative and self-organized process, capable to adapt to interference through cell-cell interactions, which are widely believed to be mediated by molecules. Analyzing intact and mechanically perturbed avian embryos, we show that the mechanical forces that drive embryogenesis self-organize in an analog of Turing's molecular reaction-diffusion model, with contractility locally self-activating and the ensuing tension acting as a long-range inhibitor. This mechanical feedback governs the persistent pattern of tissue flows that shape the embryo and steers the concomitant emergence of embryonic territories by modulating gene expression, ensuring the formation of a single embryo under normal conditions, yet allowing the emergence of multiple, well-proportioned embryos upon perturbations. Thus, mechanical forces are a central signal in embryonic self-organization, feeding back onto gene expression to canalize both patterning and morphogenesis.

Embryonic Regulation of the Mouse Hematopoietic Niche

Hematopoietic stem cells (HSCs) can differentiate into several types of hematopoietic cells (HCs) (such as erythrocytes, megakaryocytes, lymphocytes, neutrophils, or macrophages) and also undergo self-renewal to sustain hematopoiesis throughout an organism's lifetime. HSCs are currently used clinically as transplantation therapy in regenerative medicine and are typically obtained from healthy donors or cord blood. However, problems remain in HSC transplantation, such as shortage of cells, donor risks, rejection, and graft-versus-host disease (GVHD). Thus, increased understanding of HSC regulation should enable us to improve HSC therapy and develop novel regenerative medicine techniques. HSC regulation is governed by two types of activity: intrinsic regulation, programmed primarily by cell autonomous gene expression, and extrinsic factors, which originate from so-called “niche cells” surrounding HSCs. Here, we focus on the latter and discuss HSC regulation with special emphasis on the role played by niche cells.