Video #1: Transition in pulsed contractions during wild-type ventral furrow formation
Movie of embryo undergoing gastrulation. Bolded white pulses are ratcheted pulses. Lighter white pulses are unconstricting or unratcheted pulses. Cells transition from unratcheted to ratcheted pulses. Video / Shicong 'Mimi' Xie
Video #2: Twist is required for proper order of different contractile pulses
Movie of embryo depleted of Twist undergoing gastrulation. Bolded pulses are ratcheted pulses. Lighter white pulses are unconstricting or unratcheted pulses. Cells do not unidirectionally transition from having unratcheted pulses to ratcheted pulses. Video / Shicong 'Mimi' Xie
Our Dev. Cell, 2016 paper shows how nonmuscle, epithelial cells are organized and contract like a muscle to fold a tissue. Read more.
Our Dev. Cell, 2015 paper shows how cells are mechanically linked to one another so that forces are stably transmitted across a tissue. Read more.
Martin Lab research summary
“It is not birth, marriage, or death, but gastrulation, which is truly the most important time in your life.”
Lewis Wolpert
To form a complex organ, simple tissues must be folded, stretched, compressed, and otherwise sculpted into a precise form in a process called tissue morphogenesis. One of the most dramatic examples of tissue morphogenesis occurs during embryonic development, when primitive planar tissues are folded to generate separate layers that will give rise to different parts of the body during gastrulation. Tissue morphogenesis requires that cytoskeletal machines generate forces that change cell shape and deform the tissue. The molecular mechanism by which the cytoskeleton generates force is not known for many of the diverse cell shape changes and tissue movements that underlie morphogenesis. Furthermore, how force generation by hundreds or thousands of cells is coordinated by biochemical and mechanical signals in a tissue is an important step to understand how cells collectively deform a tissue.
The Martin lab is interested in how tissues get their shape. Given that tissue morphogenesis fundamentally involves movement, we have developed a system to visualize and quantify the dynamics of molecules, cells, and tissues during gastrulation. We focus on mesoderm invagination in the fruit fly, Drosophila melanogaster, because cell shape changes and cytoskeletal dynamics can be readily imaged by confocal microscopy during a process that occurs on the time scale of minutes. Live imaging can be combined with genetic (mutants, RNAi), cell biological (drug injections), computational (image segmentation and analysis), biophysical (laser cutting), and biochemical (complex purification) approaches to functionally dissect cell shape change in the embryo.
Fixed and sectioned embryos showing cell and tissue shape at various stages of cell invagination during gastrulation. Pseudo-colored in style of Andy Warhol. Image / Claudia Vasquez
Radial cell polarity
Myosin staining (green) in normal (top) and twist mutant (bottom) embryo. Myosin abnormally goes to cell interfaces in the mutant. Image / Frank Mason
Integrating forces across the tissue
Cells tear apart from each other in adherens junction mutants, leaving membrane tethers; establishing the critical role of adherens junctions in transmitting contractile forces across the tissue. Image / Adam Martin
Transition in pulsed contractions during wild-type ventral furrow formation
Movie of myosin (green) and membrane (magenta) in embryo undergoing gastrulation. Pulsed contractions identified from the embryo are shown in white overlay. Bolded white pulses are ratcheted pulses. Lighter white pulses are unconstricting or unratcheted pulses. Cells start with unratcheted or unconstricting pulses and transition to having ratcheted pulses. Video / Shicong 'Mimi' Xie
Twist is required for proper order of different contractile pulse
Movie of myosin (green) and membrane (magenta) in embryo injected with twi double stranded RNA. Pulsed contractions identified from the embryo are shown in white overlay. Bolded pulses are ratcheted pulses. Lighter white pulses are unconstricting or unratcheted pulses. Note that cells abnormally switch from having a ratcheted pulse back to having unratcheted pulses. Video / Shicong 'Mimi' Xie
