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Prostaglandin E2 (PGE 2 ) and 16,16-dimethyl-PGE 2 (dmPGE 2 ) are important regulators of hematopoietic stem and progenitor cell (HSPC) fate and offer potential to enhance stem cell therapies [C. Cutler et al. Blood 122 , 3074–3081(2013); W. Goessling et al. Cell Stem Cell 8 , 445–458 (2011); W. Goessling et al. Cell 136 , 1136–1147 (2009)]. Here, we report that PGE 2 -induced changes in chromatin at enhancer regions through histone-variant H2A.Z permit acute inflammatory gene induction to promote HSPC fate. We found that dmPGE 2 -inducible enhancers retain MNase-accessible, H2A.Z-variant nucleosomes permissive of CREB transcription factor (TF) binding. CREB binding to enhancer nucleosomes following dmPGE 2 stimulation is concomitant with deposition of histone acetyltransferases p300 and Tip60 on chromatin. Subsequent H2A.Z acetylation improves chromatin accessibility at stimuli-responsive enhancers. Our findings support a model where histone-variant nucleosomes retained within inducible enhancers facilitate TF binding. Histone-variant acetylation by TF-associated nucleosome remodelers creates the accessible nucleosome landscape required for immediate enhancer activation and gene induction. Our work provides a mechanism through which inflammatory mediators, such as dmPGE 2 , lead to acute transcriptional changes and modify HSPC behavior to improve stem cell transplantation.

SummaryStem cell transplantation presents a potentially curative strategy for genetic disorders of skeletal muscle, but this approach is limited due to the deleterious effects of cell expansionin vitroand consequent poor engraftment efficiency. In an effort to overcome this limitation, we sought to identify molecular signals that enhance the myogenic activity of cultured muscle progenitors. Here, we report the development and application of a cross-species small molecule screening platform employing zebrafish and mouse, which enables rapid, direct evaluation of the effects of chemical compounds on the engraftment of transplanted muscle precursor cells. Using this system, we screened a library of bioactive lipids to identify those that could increase myogenic engraftmentin vivoin zebrafish and mice. Two lipids, lysophosphatidic acid (LPA) and niflumic acid (NFA), are linked to activation of intracellular calcium ion flux, which showed conserved, dose-dependent and synergistic effects in promoting muscle engraftment across these vertebrate species.

Prostaglandin E2 (PGE2) and 16,16-dimethyl-PGE2 (dmPGE2) are important regulators of hematopoietic stem and progenitor cell (HSPC) fate and offer potential to enhance stem cell therapies1,2. The mechanism of gene regulation in response to dmPGE2 is poorly understood. Here, we show that dmPGE2 regulates inflammatory gene induction by modulating the chromatin architecture and activity of enhancer elements in human HSPCs. We identified the specific genomic reorganization at stimuli-responsive enhancers that permits rapid transcriptional activation. We found that dmPGE2-inducible enhancers retain MNase-accessible, H2A.Z-variant nucleosomes that are permissive to binding of the transcription factor CREB. CREB binding to enhancer nucleosomes is concomitant with deposition of the histone acetyltransferases p300 and Tip60 on chromatin. Subsequent H2A.Z acetylation improves chromatin accessibility at stimuli-responsive enhancers. Our findings support a model where histone variant nucleosomes retained within inducible enhancers facilitate transcription factor (TF) binding. Acetylation of histone variant nucleosomes by TF-associated nucleosome remodelers creates the accessible nucleosome landscape required for immediate enhancer activation and gene induction. Our work provides a mechanism by which inflammatory mediators such as dmPGE2 lead to acute transcriptional changes and alter HSPC behavior.

Pseudomonas syringae pv. tabaci ATCC 11528 produces tabtoxin, a β-lactam-containing dipeptide phytotoxin. Tabtoxinine-β-lactam (TβL), one of tabtoxin's constituent amino acids, structurally mimics lysine, and many of the proteins encoded by the tabtoxin biosynthetic gene cluster are homologs of lysine biosynthetic enzymes, suggesting that the tabtoxin and lysine biosynthetic routes parallel one another. We cloned and expressed TabB and TabD, predicted homologs of tetrahydrodipicolinate (THDPA)-N-acyltransferase and N-acyl-THDPA aminotransferase, respectively, to determine their activities in vitro. We confirmed that TabB succinylates THDPA and that TabD is a PLP-dependent aminotransferase that utilizes glutamate as an amine donor. Surprisingly, we also found that though TabD could utilize the TabB product N-succinyl-THDPA as a substrate, THDPA itself was also recognized. These observations reveal that TabB functionally duplicates DapD, the THDPA-N-succinyltransferase involved in lysine biosynthesis, and reinforce the close relationship between the metabolic logics underpinning the respective biosynthetic pathways.