Tissue analysis reveals spatial and temporal dynamics of chick limb formation.
A comprehensive map of limb development in chick embryos by researchers from RIKEN and Nagoya University has uncovered tissue-level deformation patterns of organ development. The findings reveal that the main driver of early limb formation is a global pattern of tissue stretching—and not spatial changes in organ volume, as previously believed.
“Our findings clearly refute the previous dominant model for limb elongation,” says Yoshihiro Morishita, a scientist at the RIKEN Quantitative Biology Center who teamed up with Atsushi Kuroiwa and Takayuki Suzuki of Nagoya University to undertake the developmental study.
The scientists took snapshots of a developing chick hindlimb using a simple technique based on fluorescence microscopy. They injected a fluorescent dye into the embryo to create ‘landmarks’ and then measured the positions of these points over 12-hour intervals before, during and after limb extension. Combining these pictures with a statistical method recently developed by Morishita and Suzuki, the researchers constructed accurate geometric maps of tissue dynamics.
Analysis of the spatial and temporal patterns in the maps revealed three distinct growth modes. In the first growth mode, tissue growth was concentrated in the distal end of the developing hindlimb. It then moved to the posterior region, before shifting again to proximal and anterior locations during the later stages of development.
These tissue-level, macroscopic patterns were consistent with the molecular activities of cellular growth factors known to impact limb formation at a smaller scale. Furthermore, the researchers showed that directional tissue elongation, and not local cell proliferation, had the greatest impact on determining the final limb shape.
The techniques used by Morishita and his colleagues are not limited to the analysis of chick limbs. “These same methods could be used for other organisms and other organ systems,” Morishita says. “Because of the versatility of our method, we are trying to apply it to other systems.” Such systems include the developing brain and heart.
For now, these studies remain exploratory investigations into the basic rules of organ development. “However, over the long term,” Morishita says, “once the relationships among tissue-level morphogenetic processes, cellular behaviors and molecular activities have been quantitatively elucidated, we should be able to understand and predict mechanisms of malformations of organ morphologies.” This knowledge could eventually aid the treatment of organ disorders, either by revealing drug targets or by offering clues about how to build artificial organs in the laboratory.
About this genetics research
Source:RIKEN Image Credit: Image credited to Y. Morishita et al./Development Original Research:Abstract for “Quantitative analysis of tissue deformation dynamics reveals three characteristic growth modes and globally aligned anisotropic tissue deformation during chick limb development” by Yoshihiro Morishita, Atsushi Kuroiwa and Takayuki Suzuki in Development. Published online May 1 2015 doi:10.1242/dev.109728
Quantitative analysis of tissue deformation dynamics reveals three characteristic growth modes and globally aligned anisotropic tissue deformation during chick limb development
Tissue-level characterization of deformation dynamics is crucial for understanding organ morphogenetic mechanisms, especially the interhierarchical links among molecular activities, cellular behaviors and tissue/organ morphogenetic processes. Limb development is a well-studied topic in vertebrate organogenesis. Nevertheless, there is still little understanding of tissue-level deformation relative to molecular and cellular dynamics. This is mainly because live recording of detailed cell behaviors in whole tissues is technically difficult. To overcome this limitation, by applying a recently developed Bayesian approach, we here constructed tissue deformation maps for chick limb development with high precision, based on snapshot lineage tracing using dye injection. The precision of the constructed maps was validated with a clear statistical criterion. From the geometrical analysis of the map, we identified three characteristic tissue growth modes in the limb and showed that they are consistent with local growth factor activity and cell cycle length. In particular, we report that SHH signaling activity changes dynamically with developmental stage and strongly correlates with the dynamic shift in the tissue growth mode. We also found anisotropic tissue deformation along the proximal-distal axis. Morphogenetic simulation and experimental studies suggested that this directional tissue elongation, and not local growth, has the greatest impact on limb shaping. This result was supported by the novel finding that anisotropic tissue elongation along the proximal-distal axis occurs independently of cell proliferation. Our study marks a pivotal point for multi-scale system understanding in vertebrate development.
“Quantitative analysis of tissue deformation dynamics reveals three characteristic growth modes and globally aligned anisotropic tissue deformation during chick limb development” by Yoshihiro Morishita, Atsushi Kuroiwa and Takayuki Suzuki in Development. Published online May 1 2015 doi:10.1242/dev.109728