SoxD Proteins Influence Multiple Stages of Oligodendrocyte Development and Modulate SoxE Protein Function

SummaryThe myelin-forming oligodendrocytes are an excellent model to study transcriptional regulation of specification events, lineage progression, and terminal differentiation in the central nervous system. Here, we show that the group D Sox transcription factors Sox5 and Sox6 jointly and cell-autonomously regulate several stages of oligodendrocyte development in the mouse spinal cord. They repress specification and terminal differentiation and influence migration patterns. As a consequence, oligodendrocyte precursors and terminally differentiating oligodendrocytes appear precociously in spinal cords deficient for both Sox proteins. Sox5 and Sox6 have opposite functions than the group E Sox proteins Sox9 and Sox10, which promote oligodendrocyte specification and terminal differentiation. Both genetic as well as molecular evidence suggests that Sox5 and Sox6 directly interfere with the function of group E Sox proteins. Our studies reveal a complex regulatory network between different groups of Sox proteins that is essential for proper progression of oligodendrocyte development

Substrate scope of a dehydrogenase from Sphingomonas species A1 and its potential application in the synthesis of rare sugars and sugar derivatives

Rare sugars and sugar derivatives that can be obtained from abundant sugars are of great interest to biochemical and pharmaceutical research. Here, we describe the substrate scope of a short-chain dehydrogenase/reductase from Sphingomonas species A1 (SpsADH) in the oxidation of aldonates and polyols. The resulting products are rare uronic acids and rare sugars respectively. We provide insight into the substrate recognition of SpsADH using kinetic analyses, which show that the configuration of the hydroxyl groups adjacent to the oxidized carbon is crucial for substrate recognition. Furthermore, the specificity is demonstrated by the oxidation of d-sorbitol leading to l-gulose as sole product instead of a mixture of d-glucose and l-gulose. Finally, we applied the enzyme to the synthesis of l-gulose from d-sorbitol in an in\ua0vitro system using a NADH oxidase for cofactor recycling. This study shows the usefulness of exploring the substrate scope of enzymes to find new enzymatic reaction pathways from renewable resources to value-added compounds

Enzymatic Reduction of Nicotinamide Biomimetic Cofactors Using an Engineered Glucose Dehydrogenase: Providing a Regeneration System for Artificial Cofactors

The increasing demand for chiral compounds supports the development of enzymatic processes. Dehydrogenases are often the enzymes of choice due to their high enantioselectivity combined with broad substrate acceptance. However, their requirement on costly NAD­(P)/H as cofactor has sparked interest in the development of biomimetic derivatives that are easy to synthesize and, therefore, less expensive. Until now, few reactions with biomimetics have been described and regeneration is limited to nonenzymatic means, which are not suitable for incorporation and in situ approaches. Herein, we describe a regeneration enzyme, glucose dehydrogenase from <i>Sulfolobus solfataricus</i> (<i>Ss</i>GDH), and demonstrate its activity with different biomimetics with the structure nicotinamide ring-alkyl chain-phenyl ring. Subsequent enzyme engineering resulted in the double mutant <i>Ss</i>GDH Ile192Thr/Val306Ile, which had a 10-fold higher activity with one of the biomimetics compared with the wild-type enzyme. Using this engineered variant in combination with an enoate reductase from <i>Thermus scotoductus</i> resulted in the first enzyme-coupled regeneration process for biomimetic cofactor without ribonucleotide or ribonucleotide analogue and full conversion of 10 mM 2-methylbut-2-enal with 1-phenethyl-1,4-dihydropyridine-3-carboxamide as cofactor

The Sox9 transcription factor determines glial fate choice in the developing spinal cord

The mechanism that causes neural stem cells in the central nervous system to switch from neurogenesis to gliogenesis is poorly understood. Here we analyzed spinal cord development of mice in which the transcription factor Sox9 was specifically ablated from neural stem cells by the CRE/loxP recombination system. These mice exhibit defects in the specification of oligodendrocytes and astrocytes, the two main types of glial cells in the central nervous system. Accompanying an early dramatic reduction in progenitors of the myelin-forming oligodendrocytes, there was a transient increase in motoneurons. Oligodendrocyte progenitor numbers recovered at later stages of development, probably owing to compensatory actions of the related Sox10 and Sox8, both of which overlap with Sox9 in the oligodendrocyte lineage. In agreement, compound loss of Sox9 and Sox10 led to a further decrease in oligodendrocyte progenitors. Astrocyte numbers were also severely reduced in the absence of Sox9 and did not recover at later stages of spinal cord development. Taking the common origin of motoneurons and oligodendrocytes as well as V2 interneurons and some astrocytes into account, stem cells apparently fail to switch from neurogenesis to gliogenesis in at least two domains of the ventricular zone, indicating that Sox9 is a major molecular component of the neuron–glia switch in the developing spinal cord

Terminal differentiation of myelin-forming oligodendrocytes depends on the transcription factor Sox10

Sox10 is a high-mobility-group transcriptional regulator in early neural crest. Without Sox10, no glia develop throughout the peripheral nervous system. Here we show that Sox10 is restricted in the central nervous system to myelin-forming oligodendroglia. In Sox10-deficient mice progenitors develop, but terminal differentiation is disrupted. No myelin was generated upon transplantation of Sox10-deficient neural stem cells into wild-type hosts showing the permanent, cell-autonomous nature of the defect. Sox10 directly regulates myelin gene expression in oligodendrocytes, but does not control erbB3 expression as in peripheral glia. Sox10 thus functions in peripheral and central glia at different stages and through different mechanisms

Reaction Design for the Compartmented Combination of Heterogeneous and Enzyme Catalysis

The combination of a heterogeneously catalyzed reaction with a biotransformation as a one-pot cascade process is an important strategy to reduce costs, time, and labor efforts in the production of chemicals from biogenic resources. Although one-pot cascade-type approaches generally result in more efficient chemical processes by reducing the number of workup operations needed and time consumed, the combination of different types of catalysts, both chemical and enzymatic, into a single reaction vessel often remains challenging. During our study, aimed at the direct synthesis of 2-keto-3-deoxy sugar acids as one intermediate toward biobased building blocks starting from the corresponding sugars by combining heterogeneous inorganic catalysis with enzyme catalysis, we encountered several incompatibility problems. These were overcome by a chemoenzymatic method in different compartments, which involves the gold-catalyzed direct oxidation by molecular oxygen and the subsequent conversion of the sugar acids through an enzymatic dehydration step. The described procedure represents an efficient synthesis route toward four different 2-keto-3-deoxy sugar acids and serves as a proof of concept for the combination of one-pot-incompatible catalysts under continuous flow