Local mRNA translation in growing axons allows for rapid and precise regulation of protein expression in response to extrinsic stimuli. However, the role of local translation in mature CNS axons is unknown. Such a mechanism requires the presence of translational machinery and associated mRNAs in circuit-integrated brain axons. Here we use a combination of genetic, quantitative imaging and super-resolution microscopy approaches to show that mature axons in the mammalian brain contain ribosomes, the translational regulator FMRP and a subset of FMRP mRNA targets. This axonal translational machinery is associated with Fragile X granules (FXGs), which are restricted to axons in a stereotyped subset of brain circuits. FXGs and associated axonal translational machinery are present in hippocampus in humans as old as 57 years. This FXGassociated axonal translational machinery is present in adult rats, even when adult neurogenesis is blocked. In contrast, in mouse this machinery is only observed in juvenile hippocampal axons. This differential developmental expression was specific to the hippocampus, as both mice and rats exhibit FXGs in mature axons in the adult olfactory system. Experiments in Fmr1 null mice show that FMRP regulates axonal protein expression but is not required for axonal transport of ribosomes or its target mRNAs. Axonal translational machinery is thus a feature of adult CNS neurons. Regulation of this machinery by FMRP could support complex behaviours in humans throughout life.

Elevated CO2 and nitrogen (N) addition directly affect plant productivity and the mechanisms that allow tidal marshes to maintain a constant elevation relative to sea level, but it remains unknown how these global change drivers modify marsh plant response to sea level rise. Here we manipulated factorial combinations of CO2 concentration (two levels), N availability (two levels) and relative sea level (six levels) using in situ mesocosms containing a tidal marsh community composed of a sedge, Schoenoplectus americanus, and a grass, Spartina patens. Our objective is to determine, if elevated CO2 and N alter the growth and persistence of these plants in coastal ecosystems facing rising sea levels. After two growing seasons, we found that N addition enhanced plant growth particularly at sea levels where plants were most stressed by flooding (114% stimulation in the + 10 cm treatment), and N effects were generally larger in combination with elevated CO2 (288% stimulation). N fertilization shifted the optimal productivity of S. patens to a higher sea level, but did not confer S. patens an enhanced ability to tolerate sea level rise. S. americanus responded strongly to N only in the higher sea level treatments that excluded S. patens. Interestingly, addition of N, which has been suggested to accelerate marsh loss, may afford some marsh plants, such as the widespread sedge, S. americanus, the enhanced ability to tolerate inundation. However, if chronic N pollution reduces the availability of propagules of S. americanus or other flood-tolerant species on the landscape scale, this shift in species dominance could render tidal marshes more susceptible to marsh collapse.

Astrocytes have emerged as integral partners with neurons in regulating synapse formation and function, but the mechanisms that mediate these interactions are not well understood. Here, we show that Sonic hedgehog (Shh) signaling in mature astrocytes is required for establishing structural organization and remodeling of cortical synapses in a cell type-specific manner. In the postnatal cortex, Shh signaling is active in a subpopulation of mature astrocytes localized primarily in deep cortical layers. Selective disruption of Shh signaling in astrocytes produces a dramatic increase in synapse number specifically on layer V apical dendrites that emerges during adolescence and persists into adulthood. Dynamic turnover of dendritic spines is impaired in mutant mice and is accompanied by an increase in neuronal excitability and a reduction of the glial-specific, inward-rectifying K+ channel Kir4.1. These data identify a critical role for Shh signaling in astrocyte-mediated modulation of neuronal activity required for sculpting synapses.

20Astrocytes have emerged as integral partners with neurons in regulating synapse formation and 21 function, but the mechanisms that mediate these interactions are not well understood. Here, we 22 show that Sonic hedgehog (Shh) signaling in mature astrocytes is required for establishing 23 structural organization and remodeling of cortical synapses in a cell type-specific manner. In 24 the postnatal cortex, Shh signaling is active in a subpopulation of mature astrocytes localized 25 primarily in deep cortical layers. Selective disruption of Shh signaling in astrocytes produces a 26 dramatic increase in synapse number specifically on layer V apical dendrites that emerges 27 during adolescence and persists into adulthood. Dynamic turnover of dendritic spines is 28 impaired in mutant mice and is accompanied by an increase in neuronal excitability and a 29 reduction of the glial-specific, inward-rectifying K + channel Kir4.1. These data identify a critical 30 role for Shh signaling in astrocyte-mediated modulation of neuronal activity required for 31 sculpting synapses. 32 33 34 35 36 42Astrocytes interact intimately with synapses to regulate their formation, maturation, and function, 43 and a growing number of astrocyte-secreted proteins that directly mediate synapse formation 44 and elimination have been identified 5-9 . In addition, astrocytes regulate concentrations of K + 45 and glutamate in the extracellular space, thereby modulating neuronal activity 10 . Nevertheless, 46 despite the remarkable progress in our understanding of the essential role for astrocytes in 47 regulating synaptic formation and function, the underlying signaling programs mediating 48 astrocyte-dependent regulation of synapse organization remain poorly understood. 49The molecular signaling pathway Sonic hedgehog (Shh) governs a broad array of 50 neurodevelopmental processes in the vertebrate embryo, including morphogenesis, cell 51 proliferation and specification, and axon pathfinding 11,12 . However, Shh activity persists in 52 multiple cell populations in the postnatal and adult CNS, including progenitor cells, as well as in 53 differentiated neurons and astrocytes [13][14][15][16][17] , where novel and unexpected roles for Shh activity 54 are emerging 18 . Following injury, Shh has been shown to mitigate inflammation 19,20 , and in the 55 cerebellum, Shh derived from Purkinje neurons instructs phenotypic properties of mature 56 Bergmann glia 21 . In the postnatal cortex, Shh is required for establishing local circuits between 57 two distinct projection neuron populations 16 . Shh produced by layer V neurons guides the 58 formation of synaptic connections to its layer II/III presynaptic partners, which transduce the Shh 59 signal through non-canonical, Gli-independent mechanisms. We have previously shown that 60 Shh signaling is also active in a discrete subpopulation of cortical astrocytes 17 , suggesting that 61 Shh signaling mediates both homotypic and heterotypic cellular interactions. Astrocytes 62 engaging in Shh activity are iden...

Following injury to the central nervous system, astrocytes perform critical and complex functions that both promote and antagonize neural repair. Understanding the molecular signaling pathways that coordinate their diverse functional properties is key to developing effective therapeutic strategies. In the healthy, adult CNS, Sonic hedgehog (Shh) signaling is active in mature, differentiated astrocytes. Shh has been shown to undergo injury-induced upregulation and promote neural repair. Here, we investigated whether Shh signaling mediates astrocyte response to injury. Surprisingly, we found that following an acute, focal injury, reactive astrocytes exhibit a pronounced reduction in Shh activity in a spatiotemporally-defined manner. Shh signaling is lost in reactive astrocytes at the lesion site, but persists in mild to moderately reactive astrocytes in distal tissues. Nevertheless, local pharmacological activation of the Shh pathway in astrocytes mitigates inflammation, consistent with a neuroprotective role for Shh signaling after injury. Interestingly, we find that Shh signaling is restored to baseline levels two weeks after injury, a time during which acute inflammation has largely subsided and lesions have matured. Taken together, these data suggest that endogenous Shh signaling in astrocytes is dynamically regulated in a context dependent manner. In addition, exogenous activation of the Shh pathway promotes neuroprotection mediated by reactive astrocytes.