Summary The ability of cells to count and remember their divisions could underlie many alterations that occur during development, aging, and disease. We tracked the cumulative divisional history of slow-cycling hematopoietic stem cells (HSCs) throughout adult life. This revealed a fraction of rarely dividing HSCs that contained all the long-term HSC (LT-HSC) activity within the aging HSC compartment. During adult life, this population asynchronously completes four traceable symmetric self-renewal divisions to expand its size before entering a state of dormancy. We show that the mechanism of expansion involves progressively lengthening periods between cell divisions, with long-term regenerative potential lost upon a fifth division. Our data also show that age-related phenotypic changes within the HSC compartment are divisional history dependent. These results suggest that HSCs accumulate discrete memory stages over their divisional history and provide evidence for the role of cellular memory in HSC aging.

SUMMARY In vitro modeling of human disease has recently become feasible with induced pluripotent stem cell (iPSC) technology. Here, we established patient-derived iPSCs from a Li-Fraumeni Syndrome (LFS) family and investigated the role of mutant p53 in the development of osteosarcoma (OS). LFS iPSC-derived osteoblasts (OBs) recapitulated OS features including defective osteoblastic differentiation as well as tumorigenic ability. Systematic analyses revealed that the expression of genes enriched in LFS-derived OBs strongly correlated with decreased time to tumor recurrence and poor patient survival. Furthermore, LFS OBs exhibited impaired upregulation of the imprinted gene H19 during osteogenesis. Restoration of H19 expression in LFS OBs facilitated osteoblastic differentiation and repressed tumorigenic potential. By integrating human imprinted gene network (IGN) into functional genomic analyses, we found that H19 mediates suppression of LFS-associated OS through the IGN component DECORIN (DCN). In summary, these findings demonstrate the feasibility of studying inherited human cancer syndromes with iPSCs.

Interactions between WD40 repeat domain protein 5 (WDR5) and its various partners such as mixed lineage leukemia (MLL) and c-MYC are essential for sustaining oncogenesis in human cancers. However, inhibitors that block protein-protein interactions (PPIs) between WDR5 and its binding partners exhibit modest cancer cell killing effects and lack in vivo efficacy. Here, we present pharmacological degradation of WDR5 as a promising therapeutic strategy for treating WDR5-dependent tumors and report two high-resolution crystal structures of WDR5degrader-E3 ligase ternary complexes. We identified an effective WDR5 degrader via structure-based design and demonstrated its in vitro and in vivo antitumor activities. On the basis of the crystal structure of an initial WDR5 degrader in complex with WDR5 and the E3 ligase von Hippel-Lindau (VHL), we designed a WDR5 degrader, MS67, and demonstrated the high cooperativity of MS67 binding to WDR5 and VHL by another ternary complex structure and biophysical characterization. MS67 potently and selectively depleted WDR5 and was more effective than WDR5 PPI inhibitors in suppressing transcription of WDR5-regulated genes, decreasing the chromatin-bound fraction of MLL complex components and c-MYC, and inhibiting the proliferation of cancer cells. In addition, MS67 suppressed malignant growth of MLL-rearranged acute myeloid leukemia patient cells in vitro and in vivo and was well tolerated in vivo. Collectively, our results demonstrate that structure-based design can be an effective strategy to identify highly active degraders and suggest that pharmacological degradation of WDR5 might be a promising treatment for WDR5-dependent cancers.

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The present study was undertaken to evaluate two activation methods for somatic cell nuclear transfer (SCNT), namely, fusion and simultaneous activation (FSA, fusion medium contains calcium), versus fusion followed by chemical activation (F+CA, fusion medium does not contain calcium), and to evaluate the effects of parity of recipient dogs on the success of SCNT. Oocytes retrieved from outbred dogs were reconstructed with adult somatic cells collected from an 11-year-old female dog named Missy. In the FSA method, oocytes were fused and activated at the same time using two DC pulses of 1.75 kV/cm for 15 microsec. In the F+CA method, oocytes were fused with two DC pulses of 1.75 kV/cm for 15 microsec, and then activated 1 h after fusion by 10 microM calcium ionophore for 4 m and cultured for 4 h in 1.9 mM 6-dimethylaminopurine for postactivation. Activation method had a significant impact on the production efficiency of cloned dogs. There was a significant difference in full-term pregnancy rate and percentage of live puppies between the two methods (6.3% and 38.5% for FSA and F+CA, respectively). In our study, four out of five live offspring produced by F+CA survived versus FSA, which did not result in any surviving puppies. Overall, as few as 14 dogs and 54 reconstructed embryos were needed to produce a cloned puppy. In addition, the parity of recipient bitches had no effect on the success of SCNT in canine species. Both the nullipara and multipara bitches produced live puppies following SCNT-ET.

Transcription factor (TF)‐based reprogramming of somatic tissues holds great promise for regenerative medicine. Previously, we demonstrated that the TFs GATA2, GFI1B, and FOS convert mouse and human fibroblasts to hemogenic endothelial‐like precursors that generate hematopoietic stem progenitor (HSPC)‐like cells over time. This conversion is lacking in robustness both in yield and biological function. Herein, we show that inclusion of GFI1 to the reprogramming cocktail significantly expands the HSPC‐like population. AFT024 coculture imparts functional potential to these cells and allows quantification of stem cell frequency. Altogether, we demonstrate an improved human hemogenic induction protocol that could provide a valuable human in vitro model of hematopoiesis for disease modeling and a platform for cell‐based therapeutics. Database Gene expression data are available in the Gene Expression Omnibus (GEO) database under the accession number http://www.ncbi.nlm.nih.gov/geo/query/acc.cgi?acc=GSE130361.

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ABSTRACT. Relaxin, a member of the insulin superfamily, has diverse functions in both reproductive and nonreproductive tissues. The aim of the present study was to evaluate the effects of recombinant relaxin on the in vitro maturation of porcine oocytes and their subsequent embryonic development following in vitro fertilization. Three concentrations of relaxin (1, 10, and 100 ng/ml) were used in the in vitro maturation (IVM) medium [TCM supplemented with 10% (v/v) porcine follicular fluid, 10 ng/ml of epidermal growth factor, 4 IU/ml of pregnant mare serum gonadotropin, and (only for the first 22 hr) 4 IU/ml of human chorionic gonadotropin]. Relaxin was used during the entire IVM period. Nuclear maturation of oocytes was examined under ultraviolet light following staining with bisbenzimide (Hoechst 33342) for 5 min and mounted on a glass slide. The glutathione (GSH) content in oocytes, an important indicator of cytoplasmic maturity, was measured using a micro-glutathione assay. Cryopreserved boar semen was used for in vitro fertilization. Embryos were cultured in modified NCSU-23 medium supplemented with 0.5 mM pyruvate and 5 mM lactate. Although nuclear maturation of oocytes did not vary, the GSH content in oocytes was significantly higher when cultured with 1 ng/ml (7.9 pmol/oocyte) and 10 ng/ml (8.47 pmol/oocyte) compared to a control group. However, no additional beneficial effect was observed when 100 ng/ml of relaxin was added to the IVM medium. A significantly higher rate of blastocyst formation was observed with 10 ng of relaxin (32.4%) compared to the control (14.4%) or 100 ng of relaxin (21.4%). No difference between 1 ng and 10 ng was observed in terms of the blastocyst production rate. The inner cell mass cell numbers in relaxin-treated groups were significantly higher than control, and trophectoderm cell number was the highest in the 10 ng relaxin group. Relaxin (10 ng/ml) can be supplemented in IVM medium to support the maturation of porcine oocytes. Intensive attempts have been made to establish a reliable in vitro maturation (IVM) system for porcine oocytes. Accordingly, higher oocyte maturation rate is well documented in pigs [19], and production of both in vitro fertilized (IVF) and somatic cell nuclear transfer (SCNT) offspring using in vitro matured oocytes has also been reported [2,14]. However, embryos produced by either IVF or SCNT using in vitro-matured oocytes have resulted in a much lower pregnancy rate compared to the in vivo system. Oocyte quality influences the developmental competence of embryos and the establishment and maintenance of pregnancy following embryo transfer to recipients [11]. During IVM, oocytes progressively acquire developmental competence, which involves both cytoplasmic and nuclear maturation. This is a highly coordinated process that includes morphological, ultrastructural, and transcriptional changes in the cytoplasmic and nuclear compartments of the oocyte. However, the media used for IVM and supplements added in the medium are known to affect both maturation a...