Organoids made from dissociated progenitor cells undergo tissue-like organization. This in vitro self-organization process is not identical to embryonic organ formation, but it achieves a similar phenotype in vivo. This implies genetic codes do not specify morphology directly; instead, complex tissue architectures may be achieved through several intermediate layers of cross talk between genetic information and biophysical processes. Here we use newborn and adult skin organoids for analyses. Dissociated cells from newborn mouse skin form hair primordia-bearing organoids that grow hairs robustly in vivo after transplantation to nude mice. Detailed time-lapse imaging of 3D cultures revealed unexpected morphological transitions between six distinct phases: dissociated cells, cell aggregates, polarized cysts, cyst coalescence, planar skin, and hair-bearing skin. Transcriptome profiling reveals the sequential expression of adhesion molecules, growth factors, Wnts, and matrix metalloproteinases (MMPs). Functional perturbations at different times discern their roles in regulating the switch from one phase to another. In contrast, adult cells form small aggregates, but then development stalls in vitro. Comparative transcriptome analyses suggest suppressing epidermal differentiation in adult cells is critical. These results inspire a strategy that can restore morphological transitions and rescue the hair-forming ability of adult organoids: (i) continuous PKC inhibition and (ii) timely supply of growth factors (IGF, VEGF), Wnts, and MMPs. This comprehensive study demonstrates that alternating molecular events and physical processes are in action during organoid morphogenesis and that the self-organizing processes can be restored via environmental reprogramming. This tissue-level phase transition could drive self-organization behavior in organoid morphogenies beyond the skin.

A new type of polymer-assisted self-assembly of nanospheres at a water-air interface was uncovered. By adding merely 1-3 ppm of polyethylene oxide in the water, the polystyrene nanospheres, applicable to diameters ranging from 100 nm to 1 μm, were found to gradually move closer to each other and eventually form a close-packed structure confirmed from its diffraction pattern. As it turns out, polyethylene oxides are adsorbed onto the surface of polystyrene nanospheres, giving rise to the effective screening of coulomb repulsive force between nanospheres followed by the onset of polymer-bridging effect as demonstrated from the strong suppression of Brownian motion. The resulting monolayer of close-packed polymer/nanospheres hybrid at the water-air interface with area size more than 1 cm(2) are robust and can be transferred to a substrate of any kind without serious breaking due to surface tension tearing. Our finding may provide a further extension to the scope of nanosphere lithography technique.

We utilize real-time single-molecule imaging to investigate the transient response of DNA molecules on a rigidly supported lipid membrane upon their adsorptions. Following the stochastic landing onto the membrane at a nearly spherical initial state, these DNA coils gradually relax and expand their apparent size (R 2 g,xy ) in a highly anisotropic fashion. The evolution of R 2 g,xy exhibits considerable variations among individual molecules, and its time dependence can be characterized by a generic exponential relaxation, but only after a statistical averaging over a large number of events. This evolution defines the primary relaxation timescale, which varies with the lipid composition of the membrane. The statistics and time-resolved analyses of the conformation of individual DNA coils further indicate that the interaction between the absorbing molecules and the lipid elements plays an important role in the relaxation towards the final equilibrium of this polymer-membrane complex.