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Hippo signaling controls cell cycle and restricts cell plasticity in planarians

Constant cell renewal is required to maintain healthy organs during adult homeostasis. The highly conserved Hippo signaling pathway is essential for the regulation of basic cell behaviors that underlie tissue renewal, including cell proliferation, cell differentiation, and cell death. This study by de Sousa et al. explores the role of Hippo in planarians, flatworms that continuously alter their size depending on nutrient availability, and therefore have a high rate of cellular turnover. The researchers present evidence that the main role of Hippo in planarians is not to promote proliferation but rather to control the cell cycle and maintain a stable differentiated cell fate. The image shows overgrowth generated in the planarian Schmidtea mediterranea after inhibition of Hippo signaling. The tissue was immunostained using antibodies against actin (green) and β-catenin-2 (red), which allow visualization of the epidermal cells, and nuclei are stained with DAPI (blue).

Image Credit: Nidia de Sousa