Developmental switch from morphological replication to compensatory growth for salamander lung regeneration.

Salamanders possess a pair of lungs for active air breathing, but the lung respiration is fully operational only during the late stage of development, particularly after metamorphosis. Larval salamanders mainly exchange air through the gills and skin, thus sparing the developing lungs. Salamanders can repair their lungs after injury, but a comparative analysis of regenerative responses between the lungs of young and adult animals is lacking. In this study, lung resections were performed in both larval and adult newts (Pleurodeles waltl). The cellular dynamics, tissue morphology and organ function during lung regeneration were examined and the Yap mutants were produced with CRISPR tools. We found that salamander switches the regenerative strategies from morphological replication through the blastema formation to compensatory growth via resident epithelial cells proliferation upon pulmonary resection injury as it transitions beyond metamorphosis. The larval animals achieve lung regeneration by forming a transient blastema-like structure and regrowing full-sized developing lungs, albeit unventilated. The adults repair injured lungs via massive proliferating epithelial cells and by expanding the existing alveolar epithelium without neo-alveolarization. Yap signalling promotes epithelial cell proliferation and prevents epithelial-to-mesenchymal transition to restore functional respiration. The salamanders have evolved distinct regenerative strategies for lung repair during different phases of life. Our results demonstrate a novel strategy for functional lung recovery by inducing epithelial cell proliferation to strengthen the remaining alveoli without rebuilding new alveoli.

High-resolution single-cell analysis paves the cellular path for brain regeneration in salamanders.

Salamanders are excellent models for studying vertebrate brain regeneration, with the promise of developing novel therapies for human brain lesions. Yet the molecular and cellular mechanism of salamander brain regeneration remains largely elusive. The insight into the evolution of complex brain structures that lead to advanced functions in the mammalian brain is also inadequate. With high-resolution single-cell RNA sequencing and spatial transcriptomics, three recent studies have reported the differentiation paths of cells in the salamander telencephalon in the journal Science, bringing both old and new cell types into the focus and shedding light on vertebrate brain evolution, development, and regeneration.

Oct4 dependent chromatin activation is required for chicken primordial germ cell migration.

Primordial germ cells (PGCs) are the undifferentiated progenitors of the gametes. Unlike the poor maintenance of cultured mammalian PGCs, the avian PGCs can be expanded in vitro indefinitely while preserving pluripotency and germline competence. In mammals, the Oct4 is the master transcription factor that ensures the stemness of pluripotent cells such as PGCs, but the specific function of Oct4 in chicken PGCs remains unclear. As expected, the loss of Oct4 in chicken PGCs reduced the expression of key pluripotency factors and promoted the genes involved in endoderm and ectoderm differentiation. Furthermore, the global active chromatin was reduced as shown by the depletion of the H3K27ac upon Oct4 suppression. Interestingly, the de-activated chromatin caused the down-regulation of adjacent genes which are mostly known regulators of cell junction, chemotaxis and cell migration. Consequently, the Oct4-deficient PGCs show impaired cell migration and could not colonize the gonads when re-introduced into the bloodstream of the embryo. We propose that, in addition to maintaining pluripotency, the Oct4 mediated chromatin activation is dictating chicken PGC migration.

Altered metabolic state impedes limb regeneration in salamanders.

Salamanders are unique among tetrapods in their ability to regenerate their limbs throughout life. Like other poikilothermic amphibians, salamanders also show a remarkable capacity to survive long periods of starvation. Whether the physiological reserves necessary for tissue regeneration are preserved or sacrificed in starved salamanders is unknown. In the current study, we maintained Iberian ribbed newts ( Pleurodeles waltl) under extreme physiological stress to assess the extent of regeneration and identify the molecular and cellular changes that may occur under such conditions. After 19 months of complete food deprivation, the animals exhibited extensive morphological and physiological adaptations but remained behaviorally active and vigilant. Autophagy was elevated in different tissues and the transformed gut microbiota indicated remodeling of the intestinal tract related to autophagy. Upon limb amputation in animals starved for 21 months, regeneration proceeded with progenitor cell proliferation and migration, leading to limb blastema formation. However, limb outgrowth and patterning were substantially attenuated. Blockage of autophagy inhibited cell proliferation and blastema formation in starved animals, but not in fed animals. Hence, tissue autophagy and the regenerative response were tightly coupled only when animals were under stress. Our results demonstrate that under adverse conditions, salamanders can exploit alternative strategies to secure blastema formation for limb regeneration.

Dynamics of cardiomyocyte and muscle stem cell proliferation in pig.

The cardiac and skeletal muscle tissues are both striated and contractile but their intrinsic cellular properties are distinct. The minimal cardiomyocyte proliferation and the lack of cardiac stem cells directly leads to poor heart repair in adult mammals. But in skeletal muscle, the robust proliferation of widespread muscle stem cells support efficient muscle regeneration. The endogenous cardiomyocyte and muscle stem cell proliferation has been analyzed in common laboratory animals but not in large mammals including pigs, which are more comparable to human. In this study, we rigorously examined the cell cycle dynamics of porcine cardiomyocytes and muscle stem cells through different developmental stages. Proliferative cardiomyocytes and muscle stem cells were broadly observed in the embryonic heart and limb muscle respectively. Muscle stem cells continue to proliferate postnatally but cardiomyocyte proliferation was drastically reduced after birth. However, robust cardiomyocyte cell cycle activity was detected around postnatal day 20, which could be attributed to the binucleation but not cell division. Increased proliferating cells were detected in maternal heart during early pregnancy but they represent non-cardiomyocyte cell types. The islet1 expressing cells were only identified in the embryonic and new born porcine hearts. Furthermore, the accumulated oxidative DNA damage in the cardiac but not skeletal muscle during development could be responsible for the diminished cardiomyocyte proliferation in adult pig. Similarities and differences in the proliferation of heart and skeletal muscle cells are identified in pigs across different developmental stages. Such cellular proliferative features must be taken into account when using porcine models for cardiovascular and muscular research.

Synergistic effects of TGFß2, WNT9a, and FGFR4 signals attenuate satellite cell differentiation during skeletal muscle development.

Satellite cells play a key role in the aging, generation, and damage repair of skeletal muscle. The molecular mechanism of satellite cells in these processes remains largely unknown. This study systematically investigated for the first time the characteristics of mouse satellite cells at ten different ages. Results indicated that the number and differentiation capacity of satellite cells decreased with age during skeletal muscle development. Transcriptome analysis revealed that 2,907 genes were differentially expressed at six time points at postnatal stage. WGCNA and GO analysis indicated that 1,739 of the 2,907 DEGs were mainly involved in skeletal muscle development processes. Moreover, the results of WGCNA and protein interaction analysis demonstrated that Tgfß2, Wnt9a, and Fgfr4 were the key genes responsible for the differentiation of satellite cells. Functional analysis showed that TGFß2 and WNT9a inhibited, whereas FGFR4 promoted the differentiation of satellite cells. Furthermore, each two of them had a regulatory relationship at the protein level. In vivo study also confirmed that TGFß2 could regulate the regeneration of skeletal muscle, as well as the expression of WNT9a and FGFR4. Therefore, we concluded that the synergistic effects of TGFß2, WNT9a, and FGFR4 were responsible for attenuating of the differentiation of aging satellite cells during skeletal muscle development. This study provided new insights into the molecular mechanism of satellite cell development. The target genes and signaling pathways investigated in this study would be useful for improving the muscle growth of livestock or treating muscle diseases in clinical settings.