The developmental signaling functions of cell surface heparan sulfate proteoglycans (HSPGs) are dependent on their sulfation states. Here, we report the identification of QSulf1, the avian ortholog of an evolutionarily conserved protein family related to heparan-specific N-acetyl glucosamine sulfatases. QSulf1 expression is induced by Sonic hedgehog in myogenic somite progenitors in quail embryos and is required for the activation of MyoD, a Wnt-induced regulator of muscle specification. QSulf1 is localized on the cell surface and regulates heparan-dependent Wnt signaling in C2C12 myogenic progenitor cells through a mechanism that requires its catalytic activity, providing evidence that QSulf1 regulates Wnt signaling through desulfation of cell surface HSPGs.
SUMMARYSpermidine (Spd) has been correlated with various physiological and developmental processes in plants, including pollen tube growth. In this work, we show that Spd induces an increase in the cytosolic Ca 2+ concentration that accompanies pollen tube growth. Using the whole-cell patch clamp and outside-out singlechannel patch clamp configurations, we show that exogenous Spd induces a hyperpolarization-activated Ca This messenger is hydrogen peroxide (H 2 O 2 ), and is generated during Spd oxidation, a reaction mediated by polyamine oxidase (PAO). These reactive oxygen species trigger the opening of the hyperpolarizationactivated Ca 2+ -permeable channels in pollen. To provide further evidence that PAO is in fact responsible for the effect of Spd on the Ca 2+ -permeable channels, two Arabidopsis mutants lacking expression of the peroxisomalencoding AtPAO3 gene, were isolated and characterized. Pollen from these mutants was unable to induce the opening of the Ca 2+ -permeable channels in the presence of Spd, resulting in reduced pollen tube growth and seed number. However, a high Spd concentration triggers a Ca 2+ influx beyond the optimal, which has a deleterious effect. These findings strongly suggest that the Spd-derived H 2 O 2 signals Ca 2+ influx, thereby regulating pollen tube growth.
Mechanosensitive (MS) channels are universal cellular membrane pores. Bacterial MS channels, as typified by MS channel of small conductance (MscS) from Escherichia coli (EcMscS), release osmolytes under hypoosmotic conditions. MS channels are known to be ion selective to different extents, but the underlying mechanism remains poorly understood. Here we identify an anion-selective MscS channel from Thermoanaerobacter tengcongensis (TtMscS). The structure of TtMscS closely resembles that of EcMscS, but it lacks the large cytoplasmic equatorial portals found in EcMscS. In contrast, the cytoplasmic pore formed by the C-terminal β-barrel of TtMscS is larger than that of EcMscS and has a strikingly different pattern of electrostatic surface potential. Swapping the β-barrel region between TtMscS and EcMscS partially switches the ion selectivity. Our study defines the role of the β-barrel in the ion selection of an anion-selective MscS channel and provides a structural basis for understanding the ion selectivity of MscS channels.crystal structure | anion selection | cytoplasmic region | electrophysiology | single channel recording
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