Research

Research

We study the systems morphogenesis of embryonic development at the molecular, cell, and tissue level. More specifically, we seek to uncover how molecular interactions drive cell behavior, how cell behavior shapes tissue properties, and ultimately, how the tissue properties guide embryo development. To answer these questions, we quantitatively study the process of early spinal column development in zebrafish by combining in vivo biophysics, embryology, genetics, and live imaging. Our experimental approach is driven by the idea that quantitative in vivo analysis will lead to fundamental insights into the emergence of biological organization from the collective interaction of its constituent parts.

Cell Motion in the Tailbud

The tailbud is the posterior tip of the elongating vertebrate embryo. The zebrafish tailbud is very dynamic and cells undergo successive cell state transitions from solid to fluid to solid. Picture a cell in the starting in the dorsal medial zone (DM) (see figure above). This cell moves rapidly towards the posterior in coordinated motion with its neighboring cells. If this cell is fated to become mesoderm, it will exit the DM ventrally and enter the mesodermal progenitor zone (PZ) where its motion becomes disordered relative to neighboring cells without a reduction in cell speed. This disordered cell motion underlies the fluid-like behavior of the PZ domain. Eventually, the PZ cell will join the posterior PSM, where it will reduce its speed as the PSM solidifies.

The cell state transitions in the tailbud offer many opportunities to explore cell motion. For instance, we discovered that rapid, disordered cell motion in the PZ  is required for symmetrical body elongation. The PZ also serves as a morphogen signaling center. Our lab has found that  morphogen signaling in the PZ is capable of altering cell motion outside the range of  morphogen diffusion via mechanical propagation of information.

Relevant paper from the lab:

Automated time-lapse data segmentation reveals in vivo cell state dynamics

Organization of embryonic morphogenesis via mechanical information

Patterned Disordered Cell Motion Ensures Vertebral Column Symmetry


 

Extracellular Matrix and Integrin activation

During spinal column development, the Neural Tube and PSM adhere to each other (see figure above). This inter-tissue adhesion is mediated by an extracellular matrix (ECM). Both the PSM and NT bind to a shared ECM via integrins, a class of transmembrane receptors on the cell surface. Assembly of the ECM is regulated via integrin activation. The NT/PSM interface is an excellent system for in vivo ECM function, such as understanding ECM assembly and elucidating how cells balance cell-cell and cell-ECM connections. Using living imaging, FLIM-FRET, and FCS, the lab has begun to answer these questions. We have used FCCS to measure the affinities of adhesion proteins in living embryos and FLIM-FRET to measure Integrin conformational changes and activation in vivo. 

One important component of the ECM is Fibronectin (FN) (see figure above). Fibronectin is a ligand for Integrins, and the Fibronectin matrix along the NT/PSM interface acts as a smart adhesive within an adhesive lap joint. Adhesive lap joints are used in engineering and woodworking to adhere two objects. The area of contact in the joint exhibits a stress profile, with higher stress on the outer edges of the overlap. We have created transgenic zebrafish with fluorescently tagged Fibronectin to quantify ECM dynamics in live embryos. During spinal column development, Fibronectin is continually remodeled to regions of higher stress creating a medial-lateral gradient of Fibronectin. Thus, Fibronectin acts as a smart adhesive that remodels to where it is most needed.

Relevant papers from the lab:

Integrin intra-heterodimer affinity inversely correlates with integrin activatability

Fibronectin is a smart adhesive that both influences and responds to the mechanics of early spinal column development

Cross-Scale Integrin Regulation Organizes ECM and Tissue Topology