The expression of neural-specific genes reveals the structural and molecular complexity of the planarian central nervous system

Abstract

Planarians are attractive animals in which various questions related to the central nervous system (CNS) can be addressed, such as its origin and evolution, its degree of functional conservation among different organisms, and the plasticity and regenerative capabilities of neural cells and networks. However, it is first necessary to characterize at the gene expression level how this CNS is organized in intact animals. Previous studies have shown that the planarian brain can be divided into at least three distinct domains based on the expression of otd/Otx-related genes. In order to further characterize the planarian brain, we have recently isolated a large number of planarian neural-specific genes through DNA microarrays and ESTs projects. Here, we describe new molecular domains within the brain of intact planarians by the expression of 16 planarian neural-specific genes, including the putative homologues of protein tyrosine phosphatase receptor, synaptotagmin VII, slit, G protein and glutamate and acetylcholine receptors, by in situ hybridization in both whole-mount and transverse sections. Our results indicate that planarian otd/Otx-positive domains can be further subdivided into distinct molecular regions according to the expression of different neural genes. We found differences at the gene expression level between the dorsal and ventral sides of the brain, along its antero-posterior axis and also between the proximal and distal parts of the brain lateral branches. This high level of regionalization in the planarian brain contrasts with its apparent simplicity at the morphological level.

Brain regeneration from pluripotent stem cells in planarian

“…These analyses suggested that a variety of external signals received by these sensory neurons may be integrated in the DjotxBexpressing domain, where dopaminergic neurons are concentrated (Nishimura et al 2007), and that these integrated signals may be transferred to the body muscles through the VNCs (Tazaki et al 1999). Also, additional functional domains in the planarian brain have been defined by gene expression analyses, and give us a more complex view of this organ than suggested by its relatively simple morphology (Cebrià et al 2002a). …”

“…By using a phototaxis assay system that we developed to analyse light response recovery during head regeneration, we found that light evasion is robustly re-established 5 days after amputation. Interestingly, several genes are activated at the late stage of brain regeneration, suggesting that these genes may be involved in functional recovery (Cebrià et al 2002a;Inoue et al 2004). In conclusion, brain regeneration proceeds in a sequential manner accompanied by appropriate changes of gene expression, like embryogenesis.…”

The maintenance and regeneration of the planarian excretory system are regulated by EGFR signaling

“…However, the multitude of cell types indicated by the rich and varied gene expression patterns and cell morphologies described to date make a mechanistic understanding of planarian brain regeneration a daunting endeavor (Collins et al, 2010;Nishimura et al, 2010;Nishimura et al, 2008;Nishimura et al, 2007;Cebria et al, 2002;Umesono et al, 1999). In search of a simpler structure to develop as a regenerative organogenesis model, we decided on the planarian excretory system, which consists of epithelial tubules that appear to end blindly in the mesenchyme.…”

Planarian homologs ofnetrinandnetrin receptorare required for proper regeneration of the central nervous system and the maintenance of nervous system architecture

“…After amputation, planarians can regenerate a complete CNS de novo within 1 week (Reuter et al, 1996;Cebrià et al, 2002a). Recent studies have shown both the complexity of this CNS at the molecular level, as well as a high degree of evolutionary conservation between planarian and vertebrate neural genes (Umesono et al, 1997;Umesono et al, 1999;Cebrià et al, 2002a;Cebrià et al, 2002b;Cebrià et al, 2002c;Pineda and Saló, 2002;Mineta et al, 2003;Nakazawa et al, 2003). Therefore, planarians are an attractive model in which to study regeneration and renewal of the CNS.…”