A single origin to the diverse mechanisms of metazoan neurogenesis is suggested by the involvement of common signaling components and similar classes of transcription factors. However, in many forms we lack details of where neurons arise, patterns of cell division, and specific differentiation pathway components. The sea urchin larval nervous system is composed of an apical organ, which develops from neuroepithelium and functions as a central nervous system, and peripheral neurons, which differentiate in the ciliary band and project axons to the apical organ. To reveal developmental mechanisms of neurogenesis in this basal deuterostome, we developed antibodies to SoxC, SoxB2, ELAV and Brn1/2/4 and used neurons that develop at specific locations to establish a timeline for neurogenesis. Neural progenitors express, in turn, SoxB2, SoxC, and Brn1/2/4, before projecting neurites and expressing ELAV and SynB. Using pulse-chase labeling of cells with a thymidine analog to identify cells in S-phase, we establish that neurons identified by location are in their last mitotic cycle at the time of hatching, and S-phase is coincident with expression of SoxC. The number of cells expressing SoxC and differentiating as neurons is reduced in embryos injected with antisense morpholino oligonucleotides to SoxC, SoxB2 or Six3. Injection of RNA encoding SoxC into eggs does not enhance neurogenesis. In addition, inhibition of FGF receptors (SU5402) or a morpholino to FGFR1 reduces expression of SoxC. These data indicate that there are common features of neurogenesis in deuterostomes, and that sea urchins employ developmental mechanisms that are distinct from other ambulacraria.
Summary: Urchin embryos continue to prove useful as a means of studying embryonic signaling and gene regulatory networks, which together control early development. Recent progress in understanding the molecular mechanisms underlying the patterning of ectoderm has renewed interest in urchin neurogenesis. We have employed an emerging model of neurogenesis that appears to be broadly shared by metazoans as a framework for this review. We use the model to provide context and summarize what is known about neurogenesis in urchin embryos. We review morphological features of the differentiation phase of neurogenesis and summarize current understanding of neural specification and regulation of proneural networks. Delta-Notch signaling is a common feature of metazoan neurogenesis that produces committed progenitors and it appears to be a critical phase of neurogenesis in urchin embryos. Descriptions of the differentiation phase of neurogenesis indicate a stereotypic sequence of neural differentiation and patterns of axonal growth. Features of neural differentiation are consistent with localized signals guiding growth cones with trophic, adhesive, and tropic cues. Urchins are a facile, postgenomic model with the potential of revealing many shared and derived features of deuterostome neurogenesis. genesis 52:208-221. V C 2014Wiley Periodicals, Inc.
Från redaktionen"Natur och plats" är temat för detta nummer av TfL, det första år 2012. Artikelförfattarna har korn på såväl reella som imaginära platser och landskap. Sofia Wijkmark gör nedslag i samtida svensk prosa och skriver om kusliga platser i naturen och i människans psyke, Gregers Andersen behandlar fenomenet klimatromaner -dystopiska berättelser om förstörelse till följd av exploatering av jordens resurser -, Stefan Ekman reflekterar över omgivningarnas betydelse inom fantasylitteraturen och Hanna Mühlbauer skriver om platsens implikationer i norsk topografisk poesi. Vid sidan av temat står Magnus Nilssons artikel, som behandlar nutida svensk arbetarlitteratur och dess förhållande till traditionen.Utöver de fem artiklarna innehåller numret en konferensrapport signerad Christina Sjöblad, som i Paris i december 2011 deltog i symposiet "Baudelaire dans le monde. Traditions critiques et traductions". Anna Williams reflekterar i en debattartikel över det vetenskapliga språket, en text som fungerar som aptitretare till årets TfL-konferens. Den går av stapeln i Lund den 12-13 oktober under temat "Litteraturstudiet och det akademiska språket". Mer information om konferensen finns på programbladet som medföljer detta nummer. Missa inte heller CSS:s konferens om platsens betydelse i nordisk litteratur -se annonsen på sista sidan i detta nummer.Avslutningsvis presenteras ett enkätsvar om den engelska ämnesbeteckningen inom svensk litteraturvetenskap, och allra sist återfinns en avdelning med recensioner. Numret innehåller originalillustrationer av Kari Mjåtveit.
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