SCO-spondin from embryonic cerebrospinal fluid is required for neurogenesis during early brain development

Abstract

The central nervous system (CNS) develops from the neural tube, a hollow structure filled with embryonic cerebrospinal fluid (eCSF) and surrounded by neuroepithelial cells. Several lines of evidence suggest that the eCSF contains diffusible factors regulating the survival, proliferation, and differentiation of the neuroepithelium, although these factors are only beginning to be uncovered. One possible candidate as eCSF morphogenetic molecule is SCO-spondin, a large glycoprotein whose secretion by the diencephalic roof plate starts at early developmental stages. In vitro, SCO-spondin promotes neuronal survival and differentiation, but its in vivo function still remains to be elucidated. Here we performed in vivo loss of function experiments for SCO-spondin during early brain development by injecting and electroporating a specific shRNA expression vector into the neural tube of chick embryos. We show that SCO-spondin knock down induces an increase in neuroepithelial cells proliferation concomitantly with a decrease in cellular differentiation toward neuronal lineages, leading to hyperplasia in both the diencephalon and the mesencephalon. In addition, SCO-spondin is required for the correct morphogenesis of the posterior commissure and pineal gland. Because SCO-spondin is secreted by the diencephalon, we sought to corroborate the long-range function of this protein in vitro by performing gain and loss of function experiments on mesencephalic explants. We find that culture medium enriched in SCO-spondin causes an increased neurodifferentiation of explanted mesencephalic region. Conversely, inhibitory antibodies against SCO-spondin cause a reduction in neurodifferentiation and an increase of mitosis when such explants are cultured in eCSF. Our results suggest that SCO-spondin is a crucial eCSF diffusible factor regulating the balance between proliferation and differentiation of the brain neuroepithelial cells.

CSF Protein Contents and Their Roles in Brain Development

“…A majority of proteins found in the human and rat eCSF are secreted proteins which compose 27% and 33% of the total proteins found within the CSF, respectively [16]. Although it has also been demonstrated that the protein composition of embryonic CSF is more complex than that of adult CSF, our results indicate that adult CSF has the capacity to influence the behavior of adult NSCs in the adult brain, too [1,17,18]. The amount of protein in the CSF is low (normally < 0.5%) when compared to plasma, but the protein composition of this fluid is complex [3].…”

“…The central nervous system (CNS) develops from the neural tube, a hollow structure filled with embryonic cerebrospinal fluid (eCSF) and surrounded by neuroepithelial cells. Several evidence suggest that the eCSF contains diffusible factors such as transforming growth factor-ß (TGF-ß), nerve growth factor (NGF), brain derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3), insulin-like growth factor (IGF), and hepatocyte growth factor (HGF), regulating the survival, proliferation, and differentiation of the neuroepithelium [1]. CSF is a vital signaling system involved in the development of the cerebral cortex and probably also the rest of CNS [2].…”

“…The BMPs comprising more than 20 members by now [35]. Several members of this subfamily are present in the embryonic mouse brain, with BMP4, BMP5, BMP6, and BMP7 being expressed in the CP [1,3] BMPs, have been shown to inhibit the production of oligodendrocyte precursors [36]. BMPs mediate a diverse array of developmental processes including cellular survival, proliferation, morphogenesis, lineage commitment, differentiation and apoptosis.…”

Radial Glia in Echinoderms

“…One of them is the ability to produce and secrete a glycoprotein called subcomissural organ (SCO)‐spondin (also known as Reissner’s substance). This substance has been implicated in a multitude of functions, including modulation of cell adhesion, migration, neuronal survival, differentiation, axonal growth, CNS morphogenesis, and facilitation of the cerebrospinal fluid flow (Meiniel, ; Huh et al , ; Vera et al , ). In vertebrate embryos, SCO‐spondin is transiently produced by the radial glia of the floor plate during CNS development.…”

Fetal Cerebrospinal Fluid Promotes Proliferation and Neural Differentiation of Stromal Mesenchymal Stem Cells Derived from Bone Marrow

“…These will eventually generate all the neurons and glial cells of the cerebral cortex together with the median and lateral eminence that provide post-natal neurogenesis and cortical interneurons (reviewed in (1,2). The neural tube and cephalic vesicles are filled with embryonic cerebrospinal fluid (E-CSF) which plays important roles in neural development at both embryonic and fetal stages, regulating the survival, proliferation, and neural differentiation of the neuroepithelial progenitor cells (3)(4)(5).At the start of the major phase of cortical development, high volume CSF is secreted by the ventricular choroid plexus (6). The generation of neurons and glia from proliferating neural progenitor/stem cells is a complex process (7)(8)(9).…”