Tissue scale properties of the extracellular matrix regulates nuclear shape, organisation and fate in the embryonic midline sutures

Balancing self-renewal and differentiation is a key feature of every stem cell niche and one that is tuned by mechanical interactions of cells with their neighbors and surrounding extracellular matrix. The fibrous stem cell niches that develop as sutures between skull bones must balance the complex extracellular environment that emerges to define them with self-renewal and bone production. Here, we address the role for physical stimuli in suture development by probing the relationship between nuclear shape, organization and gene expression in response to a developing collagen network in embryonic midline sutures. This work complements genetic approaches used to study sutures and provides the first quantitative analyses of physical structure in these sutures. By combining multiple imaging modalities with novel shape description, in addition to network analysis methods, we find the early emergence of a complex extracellular collagen network to have an important role in regulating morphogenesis and cell fate. We show that disrupted collagen crosslinking can alter ECM organization of midline sutures as well as stimulate expression of bone differentiation markers. Further, our findings suggest that in vivo, skeletal tissues can uncouple the response of the nuclear lamina from collagen mediated tissue stiffening seen in vitro. Our findings highlight a crucial relationship between the cellular microenvironment, tissue stiffness and geometry with gene expression in normal development and maintenance of progenitor fate in embryonic sutures.