Tissue regenerative potential displays striking divergence across phylogeny and ontogeny, but the underlying mechanisms remain enigmatic. Loss of mammalian cardiac regenerative potential correlates with cardiomyocyte cell-cycle arrest and polyploidization, as well as the development of postnatal endothermy. We reveal that diploid cardiomyocyte abundance across 41 species conforms to Kleiber’s law−the ¾-power law scaling of metabolism with bodyweight−and inversely correlates with standard metabolic rate, body temperature, and serum thyroxine level. Inactivation of thyroid hormone signaling reduces mouse cardiomyocyte polyploidization, delays cell-cycle exit, and retains cardiac regenerative potential in adults. Conversely, exogenous thyroid hormones inhibit zebrafish heart regeneration. Thus, our findings suggest that loss of heart regenerative capacity in adult mammals is triggered by increasing thyroid hormones and may be a tradeoff for the acquisition of endothermy.

Direct reprogramming of human somatic cells into pluripotency has broad implications in generating patient-specific induced pluripotent stem (iPS) cells for disease modeling and cellular replacement therapies. However, the low efficiency and safety issues associated with generation of human iPS cells have limited their usage in clinical settings. Cell types can significantly influence reprogramming efficiency and kinetics. To date, human iPS cells have been obtained only from a few cell types. Here, we report for the first time rapid and efficient generation of iPS cells from human amniotic fluid-derived cells (hAFDCs) via ectopic expression of four human factors: OCT4/SOX2/KLF4/C-MYC. Significantly, typical single iPS cell colonies can be picked up 6 days after viral infection with high efficiency. Eight iPS cell lines have been derived. They can be continuously propagated in vitro and express pluripotency markers such as AKP, OCT4, SOX2, SSEA4, TRA-1-60 and TRA-1-81, maintaining the normal karyotype. Transgenes are completely inactivated and the endogenous OCT4 promoter is adequately demethylated in the established iPS cell lines. Moreover, various cells and tissues from all three germ layers are found in embryoid bodies and teratomas, respectively. In addition, microarray analysis demonstrates a high correlation coefficient between hAFDC-iPS cells and human embryonic stem cells, but a low correlation coefficient between hAFDCs and hAFDC-iPS cells. Taken together, these data identify an ideal human somatic cell resource for rapid and efficient generation of iPS cells, allowing us to establish human iPS cells using more advanced approaches and possibly to establish disease- or patient-specific iPS cells.

POU transcription factor OCT4 not only plays an essential role in maintaining the pluripotent and self-renewing state of embryonic stem (ES) cells but also acts as a cell fate determinant through a gene dosage effect. However, the molecular mechanisms that control the intracellular OCT4 protein level remain elusive. Here, we report that human WWP2, an E3 ubiquitin (Ub)-protein ligase, interacts with OCT4 specifically through its WW domain and enhances Ub modification of OCT4 both in vitro and in vivo. We first demonstrated that endogenous OCT4 in human ES cells can be post-translationally modified by Ub. Furthermore, we found that WWP2 promoted degradation of OCT4 through the 26S proteasome in a dosage-dependent manner, and the active site cysteine residue of WWP2 was required for both its enzymatic activity and proteolytic effect on OCT4. Remarkably, our data show that the endogenous OCT4 protein level was significantly elevated when WWP2 expression was downregulated by specific RNA interference (RNAi), suggesting that WWP2 is an important regulator for maintaining a proper OCT4 protein level in human ES cells. Moreover, northern blot analysis showed that the WWP2 transcript was widely present in diverse human tissues/organs and highly expressed in undifferentiated human ES cells. However, its expression level was quickly decreased after human ES cells differentiated, indicating that WWP2 expression might be developmentally regulated. Our findings demonstrate that WWP2 is an important regulator of the OCT4 protein level in human ES cells.

Relatives of cancer patients are at an increased risk of the same (concordant) cancer but whether they are at a risk for different (discordant) cancers is largely unknown - beyond well characterized hereditary cancer syndromes - but would be of major scientific and clinical interest. We therefore decided to resolve the issue by analyzing familial risks when family members were diagnosed with any discordant cancers. We compared the population impact of concordant to discordant familial cancer. The Swedish Family-Cancer Database (FCD) was used to calculate familial relative risks (RRs) for family members of cancer patients, for the 27 most common cancers. Population attributable fractions (PAFs) were estimated for concordant and discordant family histories. Discordant cancers in the family were detected as significant risk factors for the majority of cancers, although the corresponding RRs were modest compared to RRs for concordant cancers. Risks increased with the number of affected family members with the highest RRs for pancreatic (2.31), lung (1.69), kidney (1.98), nervous system (1.79) and thyroid cancers (3.28), when 5 or more family members were diagnosed with discordant cancers. For most cancers, the PAF for discordant family history exceeded that for concordant family history. Our findings suggest that there is an unspecific genetic predisposition to cancer with clinical consequences. We consider it unlikely that shared environmental risk factors could essentially contribute to the risks for diverse discordant cancers, which are likely driven by genetic predisposition. The identification of genes that moderately increase the risk for many cancers will be a challenge.

SOX2 is a key regulator of multiple types of stem cells, especially embryonic stem cells (ESCs) and neural progenitor cells (NPCs).Understanding the mechanism underlying the function of SOX2 is of great importance for realizing the full potential of ESCs and NPCs. Here, through genome-wide comparative studies, we show that SOX2 executes its distinct functions in human ESCs (hESCs) and hESC-derived NPCs (hNPCs) through cell type-and stage-dependent transcription programs. Importantly, SOX2 suppresses non-neural lineages in hESCs and regulates neurogenesis from hNPCs by inhibiting canonical Wnt signaling. In hESCs, SOX2 achieves such inhibition by direct transcriptional regulation of important Wnt signaling modulators, WLS and SFRP2. Moreover, SOX2 ensures pluripotent epigenetic landscapes via interacting with histone variant H2A.Z and recruiting polycomb repressor complex 2 to poise developmental genes in hESCs. Together, our results advance our understanding of the mechanism by which cell type-specific transcription factors control lineage-specific gene expression programs and specify cell fate.

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The INO80 chromatin remodeler is involved in many chromatin-dependent cellular functions. However, its role in pluripotency and cell fate transition is not fully defined. We examined the impact of Ino80 deletion in the naïve and primed pluripotent stem cells. We found that Ino80 deletion had minimal effect on self-renewal and gene expression in the naïve state, but led to cellular differentiation and de-repression of developmental genes in the transition toward and maintenance of the primed state. In the naïve state, INO80 pre-marked gene promoters that would adopt bivalent histone modifications by H3K4me3 and H3K27me3 upon transition into the primed state. In the primed state, in contrast to its known role in H2A.Z exchange, INO80 promoted H2A.Z occupancy at these bivalent promoters and facilitated H3K27me3 installation and maintenance as well as downstream gene repression. Together, our results identified an unexpected function of INO80 in H2A.Z deposition and gene regulation. We showed that INO80-dependent H2A.Z occupancy is a critical licensing step for the bivalent domains, and thereby uncovered an epigenetic mechanism by which chromatin remodeling, histone variant deposition and histone modification coordinately control cell fate.

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