Stable integration of an optimized inducible promoter system enables spatiotemporal control of gene expression throughout avian development.

Precisely altering gene expression is critical for understanding molecular processes of embryogenesis. Although some tools exist for transgene misexpression in developing chick embryos, we have refined and advanced them by simplifying and optimizing constructs for spatiotemporal control. To maintain expression over the entire course of embryonic development we use an enhanced piggyBac transposon system that efficiently integrates sequences into the host genome. We also incorporate a DNA targeting sequence to direct plasmid translocation into the nucleus and a D4Z4 insulator sequence to prevent epigenetic silencing. We designed these constructs to minimize their size and maximize cellular uptake, and to simplify usage by placing all of the integrating sequences on a single plasmid. Following electroporation of stage HH8.5 embryos, our tetracycline-inducible promoter construct produces robust transgene expression in the presence of doxycycline at any point during embryonic development in ovo or in culture. Moreover, expression levels can be modulated by titrating doxycycline concentrations and spatial control can be achieved using beads or gels. Thus, we have generated a novel, sensitive, tunable, and stable inducible-promoter system for high-resolution gene manipulation in vivo.

Deciphering the Neural Crest Contribution to Cephalic Development with Avian Embryos.

For decades, the quail-chick system has been a gold standard approach to track cells and their progenies over complex morphogenetic movements and long-range migrations as well as to unravel their dialogue and interplays in varied processes of cell induction. More specifically, this model became decisive for the systematic explorations of the neural crest and its lineages and allowed a tremendous stride in understanding the wealth and complexity of this fascinating cell population. Much of our knowledge on craniofacial morphogenesis and vertebrate organogenesis was first gained in avian chimeras and later extended to mammalian models and humans. In addition, this system permits tissue and gene manipulations to be performed at once in the same cell population. Through the use of in ovo electroporation, this model became tractable for functional genomics, hence being even more resourceful for functional studies. Due to the ease of access and the possibility to combine micromanipulation of tissue anlagen and gene expression, this model offers the prospect of decrypting instructive versus permissive tissue interactions, to identify and crack the molecular codes underlying cell positioning and differentiation, with an unparalleled spatiotemporal accuracy.

Engineered Tissue Folding by Mechanical Compaction of the Mesenchyme.

Many tissues fold into complex shapes during development. Controlling this process in vitro would represent an important advance for tissue engineering. We use embryonic tissue explants, finite element modeling, and 3D cell-patterning techniques to show that mechanical compaction of the extracellular matrix during mesenchymal condensation is sufficient to drive tissue folding along programmed trajectories. The process requires cell contractility, generates strains at tissue interfaces, and causes patterns of collagen alignment around and between condensates. Aligned collagen fibers support elevated tensions that promote the folding of interfaces along paths that can be predicted by modeling. We demonstrate the robustness and versatility of this strategy for sculpting tissue interfaces by directing the morphogenesis of a variety of folded tissue forms from patterns of mesenchymal condensates. These studies provide insight into the active mechanical properties of the embryonic mesenchyme and establish engineering strategies for more robustly directing tissue morphogenesis ex vivo.