A sulfated carbohydrate epitope inhibits axon regeneration after injury.

Chondroitin sulfate proteoglycans (CSPGs) represent a major barrier to regenerating axons in the central nervous system (CNS), but the structural diversity of their polysaccharides has hampered efforts to dissect the structure-activity relationships underlying their physiological activity. By taking advantage of our ability to chemically synthesize specific oligosaccharides, we demonstrate that a sugar epitope on CSPGs, chondroitin sulfate-E (CS-E), potently inhibits axon growth. Removal of the CS-E motif significantly attenuates the inhibitory activity of CSPGs on axon growth. Furthermore, CS-E functions as a protein recognition element to engage receptors including the transmembrane protein tyrosine phosphatase PTPσ, thereby triggering downstream pathways that inhibit axon growth. Finally, masking the CS-E motif using a CS-E-specific antibody reversed the inhibitory activity of CSPGs and stimulated axon regeneration in vivo. These results demonstrate that a specific sugar epitope within chondroitin sulfate polysaccharides can direct important physiological processes and provide new therapeutic strategies to regenerate axons after CNS injury.

FARP1 promotes the dendritic growth of spinal motor neuron subtypes through transmembrane Semaphorin6A and PlexinA4 signaling.

The dendritic morphology of neurons dictates their abilities to process and transmit information; however, the signaling pathways that regulate dendritic growth and complexity are poorly understood. Here, we show that retinoids induce the expression of the FERM Rho-GEF protein FARP1 in the developing spinal cord. FARP1 is expressed in subsets of motor neurons and is enriched in dendrites of lateral motor column (LMC) neurons that innervate the limb. FARP1 is necessary and sufficient to promote LMC dendritic growth but does not affect dendrite number or axonal morphology. We show that FARP1 serves as a specific effector of transmembrane Semaphorin6A and PlexinA4 signals to regulate LMC dendritic growth, and that its Rho-GEF domain is necessary for this function. These findings reveal that retinoid and Sema6A/PlexA4 signaling pathways intersect through FARP1 to control dendritic growth, and uncover the existence of subtype-specific signaling networks that control dendritic developmental programs in spinal motor neurons.

Mesodermal and neuronal retinoids regulate the induction and maintenance of limb innervating spinal motor neurons.

During embryonic development, the generation, diversification and maintenance of spinal motor neurons depend upon extrinsic signals that are tightly regulated. Retinoic acid (RA) is necessary for specifying the fates of forelimb-innervating motor neurons of the Lateral Motor Column (LMC), and the specification of LMC neurons into medial and lateral subtypes. Previous studies implicate motor neurons as the relevant source of RA for specifying lateral LMC fates at forelimb levels. However, at the time of LMC diversification, a significant amount of retinoids in the spinal cord originates from the adjacent paraxial mesoderm. Here we employ mouse genetics to show that RA derived from the paraxial mesoderm is required for lateral LMC induction at forelimb and hindlimb levels, demonstrating that mesodermally synthesized RA functions as a second source of signals to specify lateral LMC identity. Furthermore, reduced RA levels in postmitotic motor neurons result in a decrease of medial and lateral LMC neurons, and abnormal axonal projections in the limb; invoking additional roles for neuronally synthesized RA in motor neuron maintenance and survival. These findings suggest that during embryogenesis, mesodermal and neuronal retinoids act coordinately to establish and maintain appropriate cohorts of spinal motor neurons that innervate target muscles in the limb.

Dorsal-ventral patterning: a view from the top.

The generation of dorsal interneurons in the spinal cord is dependent upon specific signaling pathways and the subsequent establishment of progenitor domains mediated by cross-repressive interactions of different groups of transcription factors. These events lead to the implementation of specific differentiation programs that direct the development of distinct dorsal interneuron subtypes. Recent studies have taken advantage of complementary gain and loss-of-function studies in the chick and mouse to clarify the in vivo roles of transforming growth factor beta signaling, basic helix-loop-helix and homeodomain transcription factors in dorsal interneuron development. The challenge now lies in identifying the precise molecular mechanisms involved and applying these insights to understanding how more ventrally located dorsal interneurons are specified.

Identification of a naturally occurring recombinant isolate of Sugarcane mosaic virus causing maize dwarf mosaic disease.

The complete nucleotide sequence of a potyvirus causing severe maize dwarf mosaic disease in Shaanxi province, northwestern China was determined (GenBank accession No. AY569692). The full genome is 9596 nucleotides in length excluding the 3 '-terminal poly (A) sequence. It contains a large open reading frame (ORF) flanked by a 149 nt 5'-untranslated region (UTR) and a 255 nt 3'-UTR. The putative polyprotein encoded by this large ORF comprises of 3063 amino acid residues. Sequence comparisons and phylogenetic analyses showed that this potyvirus is an isolate of Sugarcane mosaic virus (SCMV). The entire sequences shared identities of 89.6-97.6 % and 79.3-93.3% with 9 sequenced SCMV isolates at the nucleotide and deduced amino acid levels, respectively. But it showed much lower identities with Maize dwarf mosaic virus (MDMV), Sorghum mosaic virus (SrMV) and Johnsongrass mosaic virus (JGMV) isolates. The putative coat protein sequence is identical to that of a Chinese maize isolate SCMV-HZ. However, partition comparisons and phylogenetic profile analyses of the viral nucleotide sequences indicated that it is a recombinant isolate of SCMV. The recombination sites are located within the 6K1 and CI coding regions.

[cDNA cloning and expression in Escherichia coli of rice black-streaked dwarf virus segment 7].

Using primers designed from the terminal sequences of maize rough dwarf virus S6, a 2.2 kb cDNA fragment was amplified by RT-PCR from maize plants showing maize rough dwarf disease. Sequence analysis shows that the full length of this cDNA is 2193bp. It contains two open reading frames that encoded two polypeptides with molecular weight of 41.0kD and 36.3kD, respectively. Results of multi-sequences alignment suggest that, this cDNA sequence has significant similarity to rice black-streaked dwarf virus S7, much higher than to MRDV S6. The ORFs were cloned into expression vectors, pET21-d (ORF1) or pGEX-KG (ORF2), respectively, and then transformed to BL21(DE3)-gold. After induction with IPTG, both proteins were highly expressed. The recombinant proteins were purified and high titer antisera of these two proteins were prepared.