The kinetics of mercuric ion (Hg 2+ ) binding with heterogeneous naturally dissolved organic matter (DOM) has been hypothesized to result from competitive interactions among different organic ligands and functional groups of DOM for Hg 2+ . However, an experimental protocol is lacking to determine Hg 2+ binding with various competitive ligands and DOM, their binding strengths, and their dynamic exchange reactions. In this study, a stepwise reduction approach using ascorbic acid (AA) and stannous tin [Sn(II)] was devised to differentiate Hg(II) species in the presence of two major functional groups in DOM: the carboxylate-bound Hg(II) is reducible by both AA and Sn(II), whereas the thiolate-bound Hg(II) is reducible only by Sn(II). Using this operational approach, the relative binding strength of Hg 2+ with selected organic ligands was found in the order dimercaptopropanesulfonate (DMPS) > glutathione (GSH) > penicillamine (PEN) > cysteine (CYS) > ethylenediaminetetraacetate > citrate, acetate, and glycine at the ligand-to-Hg molar ratio < 2. Dynamic, competitive ligand exchanges for Hg 2+ from weak carboxylate to strong thiolate functional groups were observed among these ligands and within DOM, and the reaction depended on the relative binding strength and abundance of thiols and carboxylates, as well as reaction time. These results provide additional insights into dynamic exchange reactions of Hg 2+ within multicompositional DOM in controlling the transformation and bioavailability of Hg(II) in natural aquatic environments.

Cyclin-dependent kinase 5 (Cdk5) and its activator p35 are critical for radial migration and lamination of cortical neurons. However, how this kinase is regulated by extracellular and intracellular signals during cortical morphogenesis remains unclear. Here, we show that PKC␦, a member of novel PKC expressing in cortical neurons, could stabilize p35 by direct phosphorylation. PKC␦ attenuated the degradation of p35 but not its mutant derivative, which could not be phosphorylated by PKC␦. Down-regulation of PKC␦ by in utero electroporation of specific small interference RNA (siRNA) severely impaired the radial migration of cortical neurons. This migration defect was similar to that caused by down-regulation of p35 and could be prevented by cotransfection with the wild-type but not the mutant p35. Furthermore, PKC␦ could be activated by the promigratory factor brain-derived neurotrophic factor (BDNF) and was required for the activation of Cdk5 by BDNF. Both PKC␦ and p35 were required for the promigratory effect of BDNF on cultured newborn neurons. Thus, PKC␦ may promote cortical radial migration through maintaining the proper level of p35 in newborn neurons.BDNF ͉ neuronal migration ͉ phosphorylation ͉ protein stability ͉ ubiquitin

Chronic wounds caused by diabetic or venous diseases remain a social and healthcare burden. In this work, a new strategy is proposed in which injectable thermosensitive chitosan/collagen/β-glycerophosphate (β-GP) hydrogels were combined with three-dimensional mesenchymal stem cell (3D MSC) spheroids to accelerate chronic wound healing by enhanced vascularization and paracrine effects. Chitosan/collagen/β-GP solution mixed with 3D MSC spheroids was rapidly transformed to a gel at body temperature by physical cross-linking, then overlapped the wounds fully and fitted to any shape of the wound. The results showed that the combination therapy exhibited a markedly therapeutic effect than the hydrogel-loaded two-dimensional (2D) MSCs or 2D MSCs alone. The hydrogel could provide an environment conductive to the attachment and proliferation of encapsulated MSCs, especially accelerating the proliferation and paracrine factor secretion of 3D MSC spheroids. These results supplied a novel alternative approach to treat chronic wounds caused by diabetic or venous diseases.