Stem cells in organoids self-organize into tissue patterns with unknown mechanisms. Here, we use skin organoids to analyze this process. Cell behavior videos show that the morphological transformation from multiple spheroidal units with morphogenesis competence (CMU) to planar skin is characterized by two abrupt cell motility–increasing events before calming down. The self-organizing processes are controlled by a morphogenetic module composed of molecular sensors, modulators, and executers. Increasing dermal stiffness provides the initial driving force (driver) which activates Yap1 (sensor) in epidermal cysts. Notch signaling (modulator 1) in epidermal cyst tunes the threshold of Yap1 activation. Activated Yap1 induces Wnts and MMPs (epidermal executers) in basal cells to facilitate cellular flows, allowing epidermal cells to protrude out from the CMU. Dermal cell–expressed Rock (dermal executer) generates a stiff force bridge between two CMU and accelerates tissue mixing via activating Laminin and β1-integrin. Thus, this self-organizing coalescence process is controlled by a mechano-chemical circuit. Beyond skin, self-organization in organoids may use similar mechano-chemical circuit structures.

The molecular mechanism controlling regional specific skin appendage phenotypes is a fundamental question that remains unresolved. We recently identified feather and scale primordium associated genes and with functional studies, proposed five major modules are involved in scale-to-feather conversion and their integration is essential to form today’s feathers. Yet, how the molecular networks are wired and integrated at the genomic level is still unknown. Here, we combine classical recombination experiments and systems biology technology to explore the molecular mechanism controlling cell fate specification. In the chimeric explant, dermal fate is more stable, while epidermal fate is reprogrammed to be similar to the original appendage type of the mesenchyme. We analyze transcriptome changes in both scale-to-feather and feather-to-scale transition in the epidermis. We found a highly interconnected regulatory gene network controlling skin appendage types. These gene networks are organized around two molecular hubs, β-catenin and retinoic acid (RA), which can bind to regulatory elements controlling downstream gene expression, leading to scale or feather fates. ATAC sequencing analyses revealed about 1000 altered widely distributed chromatin open sites. We find that perturbation of a key gene alters the expression of many other co-expressed genes in the same module. Our findings suggest that these feather / scale fate specification genes form an interconnected network and rewiring of the gene network can lead to changes of appendage phenotypes, acting similarly to endogenous reprogramming at the tissue level. This work shows that key hub molecules, β-catenin and retinoic acid, regulate scale / feather fate specification gene networks, opening up new possibilities to understand the switches controlling organ phenotypes in a two component (epithelial and mesenchyme) system.

We compared the population dynamics of a riparian ranid frog, Rana swinhoana, before (1996–1999) and after (1999–2001) a strong earthquake. This earthquake caused little disturbance to the vegetation and landscape of the study site but the stream and ponds dried up within a week. Nearly all frogs marked (1002 of 1004) before the earthquake had disappeared after the earthquake. Smaller, unmarked frogs began to appear in stream habitats about 9 mo after the earthquake, and the frog population was much smaller than it was before the earthquake. Population dynamics and temporal and spatial distribution of frogs before and after the earthquake correlated closely with the hydrology of the stream and ponds. The movement patterns of frogs before and after the earthquake were similar, suggesting frog behavior did not change in response to drastic changes in hydrology, and frogs continued to exhibit strong site‐fidelity. Following the earthquake, stream water volume was much lower, especially in the summer, which allowed the normally winter‐breeding frogs to breed year‐round. Results demonstrate that a population of R. swinhoana can disappear suddenly as the result of a natural disturbance. We propose that anuran species that exhibit strong site‐fidelity are particularly susceptible to extirpation of local populations because frogs may lack the behavioral plasticity to respond to sudden water depletion.

The epidermal differentiation complex (EDC) encodes a group of unique proteins expressed in late epidermal differentiation. The EDC gave integuments new physicochemical properties and is critical in evolution. Recently, we showed β-keratins, members of the EDC, undergo gene cluster switching with overexpression of SATB2 (Special AT-rich binding protein-2), considered a chromatin regulator. We wondered whether this unique regulatory mechanism is specific to β-keratins or may be derived from and common to EDC members. Here we explore (1) the systematic expression patterns of non-β-keratin EDC genes and their preferential expression in different skin appendages during development, (2) whether the expression of non-β-keratin EDC sub-clusters are also regulated in clusters by SATB2. We analyzed bulk RNA-seq and ChIP-seq data and also evaluated the disrupted expression patterns caused by overexpressing SATB2. The results show that the expression of whole EDDA and EDQM sub-clusters are possibly mediated by enhancers in E14-feathers. Overexpressing SATB2 down-regulates the enriched EDCRP sub-cluster in feathers and the EDCH sub-cluster in beaks. These results reveal the potential of complex epigenetic regulation activities within the avian EDC, implying transcriptional regulation of EDC members acting at the gene and/or gene cluster level in a temporal and skin regional-specific fashion, which may contribute to the evolution of diverse avian integuments.

The integument plays a critical role in functional adaptation, with macro-regional specification forming structures like beaks, combs, feathers, and scales, while micro-regional specification modifies skin appendage shapes. However, the molecular mechanisms remain largely unknown. Craniofacial integument displays dramatic diversity, exemplified by the Polish chicken (PC) with a homeotic transformation of comb-to-crest feathers, caused by a 195–base pair (bp) duplication in HoxC10 intron. Micro-C analyses show that HoxC-containing topologically associating domain (TAD) is normally closed in the scalp but open in the dorsal and tail regions, allowing multiple long-distance contacts. In the PC scalp, the TAD is open, resulting in high HoxC expression. CRISPR-Cas9 deletion of the 195-bp duplication reduces crest feather formation, and HoxC misexpression alters feather shapes. The 195-bp sequence is found only in Archelosauria (crocodilians and birds) and not in mammals. These findings suggest that higher-order regulation of the HoxC cluster modulates gene expression, driving the evolution of adaptive integumentary appendages in birds.

In most cancers, cellular origin and the contribution of intrinsic and extrinsic factors toward transformation remain elusive. Cell specific carcinogenesis models are currently unavailable. To investigate cellular origin in carcinogenesis, we developed a tumorigenesis model based on a combination of carcinogenesis and genetically engineered mouse models. We show in organoids that treatment of any of three carcinogens, DMBA, MNU, or PhIP, with protein phosphatase 2A (PP2A) knockout induced tumorigenesis in Lgr5⁺ intestinal lineage, but not in differentiated cells. These transformed cells increased in stem cell signature, were upregulated in EMT markers, and acquired tumorigenecity. A mechanistic approach demonstrated that tumorigenesis was dependent on Wnt, PI3K, and RAS-MAPK activation. In vivo combination with carcinogen and PP2A depletion also led to tumor formation. Using whole-exome sequencing, we demonstrate that these intestinal tumors display mutation landscape and core driver pathways resembling human intestinal tumor in The Cancer Genome Atlas (TCGA). These data provide a basis for understanding the interplay between extrinsic carcinogen and intrinsic genetic modification and suggest that PP2A functions as a tumor suppressor in intestine carcinogenesis.