Signaling Cascades Governing Cdc42-Mediated Chondrogenic Differentiation and Mensenchymal Condensation

Endochondral ossification consists of successive steps of chondrocyte differentiation, including mesenchymal condensation, differentiation of chondrocytes, and hypertrophy followed by mineralization and ossification. Loss-of-function studies have revealed that abnormal growth plate cartilage of the Cdc42 mutant contributes to the defects in endochondral bone formation. Here, we have investigated the roles of Cdc42 in osteogenesis and signaling cascades governing Cdc42-mediated chondrogenic differentiation. Though deletion of Cdc42 in limb mesenchymal progenitors led to severe defects in endochondral ossification, either ablation of Cdc42 in limb preosteoblasts or knockdown of Cdc42 in vitro had no obvious effects on bone formation and osteoblast differentiation. However, in Cdc42 mutant limb buds, loss of Cdc42 in mesenchymal progenitors led to marked inactivation of p38 and Smad1/5, and in micromass cultures, Cdc42 lay on the upstream of p38 to activate Smad1/5 in bone morphogenetic protein-2-induced mesenchymal condensation. Finally, Cdc42 also lay on the upstream of protein kinase B to transactivate Sox9 and subsequently induced the expression of chondrocyte differential marker in transforming growth factor-β1-induced chondrogenesis. Taken together, by using biochemical and genetic approaches, we have demonstrated that Cdc42 is involved not in osteogenesis but in chondrogenesis in which the BMP2/Cdc42/Pak/p38/Smad signaling module promotes mesenchymal condensation and the TGF-β/Cdc42/Pak/Akt/Sox9 signaling module facilitates chondrogenic differentiation.     

Evolutionary implications of C3–C4 intermediates in the grass Alloteropsis semialata

C₄ photosynthesis is a complex trait resulting from a series of anatomical and biochemical modifications to the ancestral C₃ pathway. It is thought to evolve in a stepwise manner, creating intermediates with different combinations of C₄‐like components. Determining the adaptive value of these components is key to understanding how C₄ photosynthesis can gradually assemble through natural selection. Here, we decompose the photosynthetic phenotypes of numerous individuals of the grass Alloteropsis semialata, the only species known to include both C₃ and C₄ genotypes. Analyses of δ¹³C, physiology and leaf anatomy demonstrate for the first time the existence of physiological C₃–C₄ intermediate individuals in the species. Based on previous phylogenetic analyses, the C₃–C₄ individuals are not hybrids between the C₃ and C₄ genotypes analysed, but instead belong to a distinct genetic lineage, and might have given rise to C₄ descendants. C₃ A. semialata, present in colder climates, likely represents a reversal from a C₃–C₄ intermediate state, indicating that, unlike C₄ photosynthesis, evolution of the C₃–C₄ phenotype is not irreversible.     

Effects of Hindlimb Unweighting on MBP and GDNF Expression and Morphology in Rat Dorsal Root Ganglia Neurons

With the development of technology and space exploration, studies on long-duration space flights have shown that microgravity induces damage to multiple organs, including the dorsal root ganglia (DRG). However, very little is known about the effects of long-term microgravity on DRG neurons. This study investigated the effects of microgravity on lumbar 5 (L5) DRG neurons in rats using the hindlimb unweighting (HU) model. Male (M) and female (F) Sprague-Dawley rats were randomly divided into M- and F-control (CON) groups and M- and F-HU groups, respectively (n = 10). At the end of HU treatment for 4 weeks, morphological changes were detected. Myelin basic protein (MBP) and degenerated myelin basic protein (dgen-MBP) expressions were analyzed by immunofluorescence and western blot assays. Glial cell line-derived neurotrophic factor (GDNF) protein and mRNA expressions were also analyzed by immunohistochemistry, western blot, and RT-PCR analysis, respectively. Compared with the corresponding CON groups, the HU groups exhibited slightly loose junctions between DRG neurons, some separated ganglion cells and satellite cells, and lightly stained Nissl bodies that were of smaller size and had a scattered distribution. High levels of dgen-MBP and low MBP expressions were appeared and GDNF expressions were significantly decreased in both HU groups. Changes were more pronounced in the F-HU group than in the M-HU group. In conclusion, HU treatment induced damage of L5 DRG neurons, which was correlated with decreased total MBP protein expression, increased dgen-MBP expression, and reduced GDNF protein and mRNA expression. Importantly, these changes were more severe in F-HU rats compared with M-HU rats.

     

Construction of a high-density SNP genetic map in flue-cured tobacco based on SLAF-seq

Tobacco (Nicotiana tabacum L., 2n = 48) is an important agronomic crop and model plant. Flue-cured tobacco is the most important type and accounts for approximately 80 % of tobacco production worldwide. The low genetic diversity of flue-cured tobacco impedes the construction of a high-density genetic linkage map using simple sequence repeat (SSR) markers and warrants the exploitation of single nucleotide polymorphic (SNP) markers from genomic regions. In this article, initially using specific locus-amplified fragment sequencing, we discovered 10,891 SNPs that were subsequently used as molecular markers for genetic map construction. Combined with SSR markers, a final high-density genetic map was generated containing 4215 SNPs and 194 SSRs distributed on 24 linkage groups (LGs). The genetic map was 2662.43 cM in length, with an average distance of 0.60 cM between adjacent markers. Furthermore, by mapping the SNP markers to the ancestral genomes of Nicotiana tomentosiformis and Nicotiana sylvestris, a large number of genome rearrangements were identified as occurring after the polyploidization event. Finally, using this novel integrated map and mapping population, two major quantitative trait loci (QTLs) were identified for flue-curing and mapped to the LG6 of tobacco. This is the first report of SNP markers and a SNP-based linkage map being developed in tobacco. The high-density genetic map and QTLs related to tobacco curing will support gene/QTL fine mapping, genome sequence assembly and molecular breeding in tobacco.     

Functional incorporation of the pore forming segment of AChR M2 into tethered bilayer lipid membranes

Tethered bilayer lipid membranes (tBLMs) are robust and flexible model platforms for the investigation of various membrane related processes. They are especially suited to study the incorporation and function of ion channel proteins, where a high background resistance of the membrane is essential. Synthetic M2 peptides, analogues of the transmembrane fragment of the acetylcholine receptor, could be incorporated into two different membrane architectures. The functional reconstitution and the formation of a conducting pore are shown by electrochemical impedance spectroscopy (EIS). The pore is selective for small monovalent cations, while bulky ions cannot pass. This is a significant step towards a novel biosensing approach. We envision a device, where a stable and insulating membrane would be attached to an electronic read-out unit and embedded proteins would serve as actual sensing units.     

Effect of a disulfide bond on mevalonate kinase

Mevalonate kinase is one of ATP-dependent enzymes in the mevalonate pathway and catalyzes the phosphorylation of mevalonate to form mevalonate 5-phosphate. In animal cells, it plays a key role in regulating biosynthesis of cholesterol, while in microorganisms and plants, it is involved in the biosynthesis of isoprenoid derivatives that are one of the largest groups of natural products. Crystal structure and sequence alignment show that a unique disulfide bond exists in mevalonate kinase of thermostable species Methanococcus jannaschii, but not in rat mevalonate kinase. In the present study, we investigated the effect of the disulfide bond in M. jannaschii mevalonate kinase and an engineered disulfide bond in rat mevalonate kinase mutant A141C on the properties of enzymes through characterization of their wild-type and variant enzymes. Our result suggests that the Cys107-Cys281 disulfide bond is important for maintaining the conformation and the thermal activity of M. jannaschii mevalonate kinase. Other interactions could also have contributions. The thiol-titration and fluorescence experiment further indicate that rat mevalonate kinase A141C variant enzyme has a new disulfide bond, which makes the variant protein enhance its thermal activity and resist to urea denaturation.