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. 2017 Oct 17;11:28. doi: 10.3389/fnint.2017.00028

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Copyright © 2017 Yu, Griffiths and Haupt.

This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

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Representation of heparan sulfate proteoglycans (HSPGs) expressed by cells at various stages of neural stem cell differentiation into neuron, astrocyte and oligodendrocyte lineages. At the stem cell state (denoted in gray), neuroepithelial cells/neural stem cell (Step 1) expresses the HSPGs syndecan-1 (SDC1), syndecan-4 (SDC4), glypican-1 (GPC1), glypican-4 (GPC4), and perlecan (PER). These HSPGs mediate cell proliferation and maintenance of the pluripotent state via FGF and Wnt signaling. As cells begin to enter differentiation programs, they become radial glia (Step 2), with the potential to differentiate into the three main neural lineages: neurons, astrocytes and oligodendrocytes. At this stage, radial glia cells express SDC1, GPC1, and GPC4. Differentiation toward the neuronal lineage (denoted in green) results in the formation of neural progenitor cells (neuronal Step 3), which expresses GPC1 and GPC4. As cells progresses to immature neurons (neuronal Step 4), syndecan-2 (SDC2) is expressed on dendritic spines to promote dendritic maturation; syndecan-3 (SDC3) is localized to axons to assist axon guidance with GPC1 during synapse formation. This is also observed in mature neurons (neuronal Step 5) in conjunction with GPC4 mediation of excitatory synapse development through LRRTM4 binding. In astrocyte lineage differentiation (denoted in red), as radial glia cells differentiate toward astrocytes, SDC1 expression diminishes, SDC4 and glypican-6 (GPC6) expression becomes detectable while GPC1 and GPC4 expression is retained (astrocyte Step 3). The presence of PER is inhibitory to astrocyte proliferation due to the presence of domain V (astrocyte Step 3). In the oligodendrocyte lineage (denoted in blue), oligodendrocyte precursor cells (oligodendrocyte Step 3) derived from radial glia cells retain SDC1 and GPC1 expression, with these HSPGs assisting in cell proliferation and inhibiting differentiation. SDC3 and PER expression are up-regulated at this stage. As oligodendrocytes are formed (oligodendrocyte Step 4), SDC2 and SDC4 become the predominately expressed HSPGs, along with PER. (Inset) Legend: Syndecan-1-4 (SDC1-4). E, ectodomain; TM, transmembrane domain; C, cytoplasmic domain, including two conserved regions C1 and C2, and a variable region (V). Perlecan (PER) comprised of domains I-V. Glypican-1, −4, and −6 (GPC1, GPC4, and GPC6) are attached to the cell surface via a GPI-anchor. Astrocyte image obtained from: https://commons.wikimedia.org/wiki/File:Diagram_of_an_astrocyte_-_a_type_of_glial_cell_CRUK_029.svg. Mature neuron image modified from: https://online.science.psu.edu/bisc004_activewd001/node/1907.