Data represents average ± SD (n = 50 - 75 cells, 3 cultures each). Treatments included transfection with GFP-LKB1 S431D, NP1-siRNA or control siRNA. Substrates were stripe-coated with BSA, Sema3A, BDNF, NGF, netrin1, F-cAMP, or F-cGMP, either alone or together with KT5720 or KT5823. Data shown are average PIs for axon/dendrite differentiation for neurons with somata located on the stripe boundary (a), and pathfinding for all neurons (b), determined at 48-60 hr after cell plating. Preference index (PI) was defined as / 100%. (C) Summary of preferential axon/dendrite differentiation (a) and pathfinding (b) for all neurons cultured on substrates striped with various factors indicated. (b) Angular locations of all initiation sites, either “on-stripe” (blue circles) or “off-stripe” (black circles), for axons (30 cells) and dendrites (10 cells) initiated on substrates striped with Sema3A, BDNF, NGF, or netrin1. The initiation site (marked by the circle) was determined relative to the center of the stripe boundary intersecting the soma (axon, green dendrites, red). (a) Schematic diagram depicts the determination of the angular location of neurite initiation sites on the soma for all neurites that became the axon or dendrites at 48-60 hr. (B) Preferential axon/dendrite differentiation was quantified retrospectively at 48-60 hr after plating, for polarized neurons with somata located at the stripe boundary. Yellow symbols mark axon/dendrite turning at the stripe boundary. White arrows and arrowheads mark neurites that later became the axon and dendrites, respectively. (A) Images of an example hippocampal neuron cultured on substrates coated with stripes (blue) of Sema3A, taken at 12 and 60 hr after cell plating and immunostaining (at 60 hr) for axons and dendrites with smi-312 and MAP2 antibodies, respectively. Thus, Sema3A regulates the earliest step of neuronal morphogenesis by polarizing axon/dendrite formation.Ĭopyright © 2011 Elsevier Inc. Downregulating Sema3A signaling in rat embryonic cortical progenitors via in utero electroporation of siRNAs against the Sema3A receptor neuropilin-1 also resulted in polarization defects in vivo. Fluorescence resonance energy transfer (FRET) imaging showed that Sema3A elevated the cGMP but reduced cAMP and protein kinase A (PKA) activity, and its axon suppression is attributed to the downregulation of PKA-dependent phosphorylation of axon determinants LKB1 and GSK-3β. Exposure of the undifferentiated neurite to localized Sema3A suppressed its differentiation into axon and promoted dendrite formation, resulting in axon formation away from the Sema3A source, and bath application of Sema3A to polarized neurons promoted dendrite growth but suppressed axon growth. We found that it also acts as a polarizing factor for axon/dendrite development in cultured hippocampal neurons. All rights reserved.Semaphorin 3A (Sema3A) is a secreted factor known to guide axon/dendrite growth and neuronal migration. Failure of axon regeneration in the adult mammalian CNS is a major problem in multiple diseases, and understanding how 5-HT receptors signal opposing effects on neurite growth may lead to novel neuroregenerative therapies, by targeting either 5-HT receptors or their downstream signaling pathways.Ĭopyright © 2012 Elsevier Inc. 5-HT predominantly appears to suppress neurite growth, but depending on the model system and 5-HT receptor subtype, in rare cases, it may promote neurite outgrowth and elongation. 5-HT has been shown to regulate neurite growth in multiple systems and species, including in the mammalian CNS. Here, we review the less well-studied role of 5-HT as a modulator of neurite growth. Although its most prominent biological function is as a signal transmission messenger from pre- to postsynaptic neurons, other roles such as shaping brain development and regulating neurite growth have also been described. The neurotransmitter serotonin (5-hydroxytryptamine, 5-HT) plays multiple roles in the enteric, peripheral, and central nervous systems (CNS).
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