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4437MA-CVE sample. The technical assistance of Mrs. L. Mansuy in the synthesis of dialkyl viologens is also gratefully acknowledged. Registry No. di-C4 viologen, 36437-30-6; di-C, viologen, 6 159-05-3; di-C8 viologen, 32449-1 8-6; di-C4 viologen radical cation, 87922-26-7; di-C, viologen radical cation, 631 19-42-6; di-C8 viologen radical cation, 49765-26-6; PSSH, 50851-57-5; MA-CVE, 26935-44-4. have tried to interpret the data on semiquantitative grounds after having developed a kinetic model which takes very satisfactorily into account the disappearance of the reduced viologens in the absence of stabilizing agent. Acknowledgment.We are indebted to Dr. E. Pefferkorn (Institut Charles Sadron, Strasbourg) for providing us with the Photoreduction of C02 to formic acid (HCO,) and a small quantity of carbon monoxide (CO) can be achieved in nonaqueous polar solvent by using oligob-phenylenes) (OPP-n) as a photocatalyst and triethylamine (TEA) as a sacrificial electron donor under >290-nm irradiation, where the photocatalysis in N,N-dimethylformamide leads to the most effective formation of HC0,-and CO. Among OPP-n, OPP-3 and OPP-4 show high photocatalytic activity for the formation of HC02-, in which the apparent quantum yields of HCOT formation for OPP-3 and OPP-4 are 0.072 and 0.084, respectively. Although photocatalyst OPP-3 itself concurrently undergoes photo-Birch reduction during the photocatalysis, the turnover number for the formation of HC02-based on the reacted OPP-3 is calculated to be 4, implying a cyclic activity of the reduction system. The laser flash photolysis and pulse radiolysis studies reveal that the photocatalysis initially starts from the reductive quenching of the singlet state of OPP-n by TEA followed by the formation of the radical anion of OPP-n, OPP-n'-, resulting in direct electron transfer from OPP-n'-to C 0 2 molecules.

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In many animals, germline progenitors are kept undifferentiated to give rise to germline stem cells (GSCs), enabling continuous production of gametes throughout animal life. In the Drosophila ovary, GSCs arise from a subset of primordial germ cells (PGCs) that stay undifferentiated even after gametogenesis has started. How a certain population of PGCs is protected against differentiation, and the significance of its regulatory mechanisms on GSC establishment remain elusive. Here we show that epidermal growth factor receptor (Egfr) signaling in somatic stromal intermingled cells (ICs), activated by its ligand produced in germ cells, controls the size of the PGC pool at the onset of gametogenesis. Egfr signaling in ICs limits the number of cells that express the heparan sulfate proteoglycan Dally, which is required for the movement and stability of the locally-produced stromal morphogen, Decapentaplegic (Dpp, a BMP2/4 homologue). Dpp is received by PGCs and maintains them in an undifferentiated state. Altering Egfr signaling levels changes the size of the PGC pool and affects the number of GSCs established during development. While excess GSC formation is compensated by the adult stage, insufficient GSC formation can lead to adult ovarioles that completely lack GSCs, suggesting that ensuring an absolute size of the PGC pool is crucial for the GSC system.

Nutrients affect adult stem cells through complex mechanisms involving multiple organs. Adipocytes are highly sensitive to diet and have key metabolic roles, and obesity increases the risk for many cancers. How diet-regulated adipocyte metabolic pathways influence normal stem cell lineages, however, remains unclear. has highly conserved adipocyte metabolism and a well-characterized female germline stem cell (GSC) lineage response to diet. Here, we conducted an isobaric tags for relative and absolute quantification (iTRAQ) proteomic analysis to identify diet-regulated adipocyte metabolic pathways that control the female GSC lineage. On a rich (relative to poor) diet, adipocyte Hexokinase-C and metabolic enzymes involved in pyruvate/acetyl-CoA production are upregulated, promoting a shift of glucose metabolism toward macromolecule biosynthesis. Adipocyte-specific knockdown shows that these enzymes support early GSC progeny survival. Further, enzymes catalyzing fatty acid oxidation and phosphatidylethanolamine synthesis in adipocytes promote GSC maintenance, whereas lipid and iron transport from adipocytes controls vitellogenesis and GSC number, respectively. These results show a functional relationship between specific metabolic pathways in adipocytes and distinct processes in the GSC lineage, suggesting the adipocyte metabolism-stem cell link as an important area of investigation in other stem cell systems.