4D quantification of animal appendage morphogenesis and diversification in the crustacean model Parhyale hawaiensis
We have established the crustacean amphipod Parhyale hawaiensis as an attractive model for developmental genetic and molecular cell biology studies. Parhyale offers a unique capacity among animal models for microscopic live imaging and tracking of all cells of developing appendages continuously from early specification up to late differentiation stages. Parhyale embryos are direct developers, they are amenable to all sorts of embryological and functional genetic manipulations, and they exhibit a striking morphological gradation along the anterior-posterior body axis. Each embryo develops a variety of specialized appendages that differ in size, shape and pattern, offering exceptional material to study the cellular and molecular basis of tissue morphogenesis. Using multi-view fluorescence light-sheet microscopy, we are able to image developing appendages at single-cell resolution over several days of embryogenesis. In parallel, we are developing image processing and analysis platforms that allow navigation through these terabyte-range data sets, as well as cell tracking and cell lineage reconstruction from multiple views of the same embryo. Using these tools, we are analyzing systematically the cell behaviors underlying the morphological diversification of Parhyale serially homologous appendages. In addition, we are making the link between developmental gene activity and morphogenetic cell behaviors by combining live imaging with functional genetic approaches for visualization and manipulation of gene expression in vivo.
Cell and tissue dynamics driving Tribolium embryo morphogenesis
We have also combined fluorescence live imaging with functional genetic approaches in the beetle Tribolium castaneum to associate early embryonic patterning with embryonic tissue morphogenesis. During these stages, the uniform single-layered Tribolium blastoderm undergoes a remarkable transformation into the condensed multi-layered embryo covered by two extraembryonic epithelia, the amnion and serosa. Our model postulates that condensation of the embryonic rudiment is an autonomous process effected by cell contraction and intercalation; that embryonic condensation drives initiation of amnion folding; and that contractile forces exerted by an actomyosin cable at the leading edge of the serosa drive expansion of the amniotic fold and closure of the amniotic cavity. These are all testable hypotheses that will be addressed with integrated developmental genetic, cell biology, biophysical and quantitative modeling approaches.
Hox control of gene regulatory networks during Drosophila appendage morphogenesis
We have employed Drosophila melanogaster, the premier model for genetic and genomic research, to study the temporal dynamics of Hox-controlled transcriptional networks. The Hox gene Ultrabithorax (Ubx) regulates hundreds of direct target genes in developing halteres in a striking stage-specific manner. This stage specificity of Ubx action may reflect extensive regulatory interactions between Hox and hormonal cues to orchestrate complex genetic programs during metamorphosis, and/or it may be associated with global changes in chromatin architecture during developmental progression.