Ecrg4 expression and its product augurin in the choroid plexus: impact on fetal brain development, cerebrospinal fluid homeostasis and neuroprogenitor cell response to CNS injury
Authors: Gonzalez Ana Maria , Podvin Sonia , Lin Shuh-Yow , Miller Miles C , Botfield Hannah , Leadbeater Wendy E , Roberton Andrew , Dang Xitong , Knowling Stuart E , Cardenas-Galindo Elena , Donahue John E , Stopa Edward G , Johanson Conrad E , Coimbra Raul , Eliceiri Brian P , Baird Andrew 
Published: January 2011

Background

The content and composition of cerebrospinal fluid (CSF) is determined in large part by the choroid plexus (CP) and specifically, a specialized epithelial cell (CPe) layer that responds to, synthesizes, and transports peptide hormones into and out of CSF. Together with ventricular ependymal cells, these CPe relay homeostatic signals throughout the central nervous system (CNS) and regulate CSF hydrodynamics. One new candidate signal is augurin, a newly recognized 14 kDa protein that is encoded byesophageal cancer related gene-4(Ecrg4), a putative tumor suppressor gene whose presence and function in normal tissues remains unexplored and enigmatic. The aim of this study was to explore whetherEcrg4and its product augurin, can be implicated in CNS development and the response to CNS injury.

Methods

Ecrg4gene expression in CNS and peripheral tissues was studied byin situhybridization and quantitative RT-PCR. Augurin, the protein encoded byEcrg4, was detected by immunoblotting, immunohistochemistry and ELISA. The biological consequence of augurin over-expression was studied in a cortical stab model of rat CNS injury by intra-cerebro-ventricular injection of an adenovirus vector containing theEcrg4cDNA. The biological consequences of reduced augurin expression were evaluated by characterizing the CNS phenotype caused byEcrg4gene knockdown in developing zebrafish embryos.

Results

Gene expression and immunohistochemical analyses revealed that, the CP is a major source ofEcrg4in the CNS and thatEcrg4mRNA is predominantly localized to choroid plexus epithelial (CPe), ventricular and central canal cells of the spinal cord. After a stab injury into the brain however, both augurin staining andEcrg4gene expression decreased precipitously. If the loss of augurin was circumvented by over-expressingEcrg4 in vivo, BrdU incorporation by cells in the subependymal zone decreased. Inversely, gene knockdown ofEcrg4in developing zebrafish embryos caused increased proliferation of GFAP-positive cells and induced a dose-dependent hydrocephalus-like phenotype that could be rescued by co-injection of antisense morpholinos withEcrg4mRNA.

Conclusion

An unusually elevated expression of theEcrg4gene in the CP implies that its product, augurin, plays a role in CP-CSF-CNS function. The results are all consistent with a model whereby an injury-induced decrease in augurin dysinhibits target cells at the ependymal-subependymal interface. We speculate that the ability of CP and ependymal epithelium to alter the progenitor cell response to CNS injury may be mediated, in part byEcrg4. If so, the canonic control of its promoter by DNA methylation may implicate epigenetic mechanisms in neuroprogenitor fate and function in the CNS.