Neural stem cells (NSCs) are uncommitted cells of the CNS defined by their multipotentiality and ability to self renew. We found these cells to not be present in substantial numbers in the CNS until after embryonic day (E) 10.5 in mouse and E5 in chick. This coincides with the induction of SOX9 in neural cells. Gain- and loss-of-function studies indicated that SOX9 was essential for multipotent NSC formation. Moreover, Sonic Hedgehog was able to stimulate precocious generation of NSCs by inducing Sox9 expression. SOX9 was also necessary for the maintenance of multipotent NSCs, as shown by in vivo fate mapping experiments in the adult subependymal zone and olfactory bulbs. In addition, loss of SOX9 led ependymal cells to adopt a neuroblast identity. These data identify a functional link between extrinsic and intrinsic mechanisms of NSCs specification and maintenance, and establish a central role for SOX9 in the process.

The secreted ligand Sonic Hedgehog (Shh) organizes the pattern of cellular differentiation in the ventral neural tube. For the five neuronal subtypes, increasing levels and durations of Shh signaling direct progenitors to progressively more ventral identities. Here we demonstrate that this mode of action is not applicable to the generation of the most ventral cell type, the nonneuronal floor plate (FP). In chick and mouse embryos, FP specification involves a biphasic response to Shh signaling that controls the dynamic expression of key transcription factors. During gastrulation and early somitogenesis, FP induction depends on high levels of Shh signaling. Subsequently, however, prospective FP cells become refractory to Shh signaling, and this is a prerequisite for the elaboration of their identity. This prompts a revision to the model of graded Shh signaling in the neural tube, and provides insight into how the dynamics of morphogen signaling are deployed to extend the patterning capacity of a single ligand. In addition, we provide evidence supporting a common scheme for FP specification by Shh signaling that reconciles mechanisms of FP development in teleosts and amniotes.[Keywords: Shh signaling; neural tube; floor plate; FoxA2] Supplemental material is available at http://www.genesdev.org.

Sonic hedgehog signalling is essential for the embryonic development of many tissues including the central nervous system, where it controls the pattern of cellular differentiation. A genome-wide screen of neural progenitor cells to evaluate the Shh signalling-regulated transcriptome identified the forkhead transcription factor Foxj1. In both chick and mouse Foxj1 is expressed in the ventral midline of the neural tube in cells that make up the floor plate. Consistent with the role of Foxj1 in the formation of long motile cilia, floor plate cells produce cilia that are longer than the primary cilia found elsewhere in the neural tube, and forced expression of Foxj1 in neuroepithelial cells is sufficient to increase cilia length. In addition, the expression of Foxj1 in the neural tube and in an Shh-responsive cell line attenuates intracellular signalling by decreasing the activity of Gli proteins, the transcriptional mediators of Shh signalling. We show that this function of Foxj1 depends on cilia. Nevertheless, floor plate identity and ciliogenesis are unaffected in mouse embryos lacking Foxj1 and we provide evidence that additional transcription factors expressed in the floor plate share overlapping functions with Foxj1. Together, these findings identify a novel mechanism that modifies the cellular response to Shh signalling and reveal morphological and functional features of the amniote floor plate that distinguish these cells from the rest of the neuroepithelium.

The blackspot seabream, Pagellus bogaraveo, is a sparid fish of great economic importance in the northeast Atlantic. The main aim of this work was to assess the infection levels and diversity of anisakid nematodes parasitizing P. bogaraveo from Portuguese waters. The anisakid larvae were identified by polymerase chain reaction-restriction fragment length polymorphism analysis and ten different patterns were observed, four of which were not previously reported in the literature. Moreover, several species were detected for the first time in this host: Anisakis simplex × Anisakis pegreffii hybrids, Anisakis ziphidarum, Anisakis typica, Anisakis physeteris, as well as three undescribed anisakids Anisakis sp. PB-2009, Anisakis sp. PB-2010, and Contracaecum sp. PB-2010. The ITS1-5.8S-ITS2 region was sequenced and analyzed phylogenetically, revealing that our anisakids were distributed by the two distinct clades reported previously, corresponding to the two recognized larval morphotypes. Moreover, a group of organisms, including our specimens from Madeira and the previously reported Anisakis sp. HC-2005, cluster together and seem to belong to clade I. A certain degree of intraspecific diversity was also detected. Samples from mainland waters had the highest infection levels and were dominated by A. pegreffii. Madeira had the highest diversity overall, dominated by Anisakis sp. PB-2010. Fish from the Azores had the lowest infection levels, and the species with the highest relative abundance was A. physeteris. The anisakid nematode communities were relatively similar in mainland waters but very distinct in both the Azores and Madeira islands, suggesting the existence of at least three different stocks of P. bogaraveo in the northeast Atlantic.

RGS2 and RGS4 mRNAs are regulated in the rat striatum by dopaminergic agents. The present study further characterizes this regulation in three experiments. First, dopamine type 1 (receptor) (D1)- and dopamine type 2 (receptor) (D2)-mediated regulator of G-protein signalling (RGS) gene regulation was investigated in animals with deleted ascending dopaminergic pathways. We showed that RGS2 expression is controlled by D1 receptors either by direct action on D1 receptors or indirectly by presynaptic D2 receptors. Conversely, RGS4 gene expression is independent of presynaptic D2 receptors. Second, the study of colocalization between RGS2 or RGS4 and D1 or D2 by double labelling in situ hybridization histochemistry revealed broad expression of RGS2 and RGS4 mRNA in striatal subpopulations with colocalization of RGS2 and RGS4 with both D1 and D2 receptors. Finally, to test how far their gene regulation is temporally concerted, changes in RGS2 and RGS4 mRNA levels were measured in parallel with receptor occupancy by specific dopaminergic drugs at different time-points. RGS2 was rapidly/transiently up-regulated by the D1 agonist SKF82958 and the D2 antagonist haloperidol (peak at 0.5 h) and down-regulated by the D1 antagonist SCH23390 and the D2 agonist quinpirole (trough at 1 and 2 h). RGS4 showed a delayed/transient up-regulation with SCH23390 and quinpirole (peak at 4 and 2 h) and down-regulation with haloperidol (trough at 8 h). Depending on the drug used, the degree of receptor occupancy did (D1 agonist and RGS2) or did not (D2 antagonist and RGS2) run parallel to RGS gene expression changes, indicating that certain drug effects are direct and others indirect. The precise control of RGS2 and RGS4 expression by dopamine receptors pleads in favour of their potential contribution to the fine-tuning of D1 and D2 receptor signalling cascades.