Cover: Light microscopy image at 40× frozen section of e18.5 mouse Col2-Cre−/−;Smad4fl/fl wild-type proximal tibial growth plate. Safranin-O (pink) demonstrates proteoglycans in the extracellular matrix. Fast Green (blue) demonstrates the chondrocyte nuclei. The Safranin-O stain demonstrates normal proteoglycan distribution in the wild-type Col2-Cre−/−;Smad4fl/fl mouse proximal tibial growth plate. On page 358, Whitaker et al. discuss the loss of proteoglycan in the Smad4 conditional knockout mouse. Image provided by Amanda T. Whitaker and licensed under a Creative Commons Attribution 4.0 International licence.