Specific Glycoproteins of the Subcommissural Organ/Reissner’s Fiber Complex: Molecular and Functional Evidence of Their Involvement in Developmental Events

Abstract

The subcommissural organ (SCO) is a phylogenetically old structure of the vertebrate brain made up of ependymal cells which secrete glycoproteins basally towards the leptomeningeal spaces and apically into the ventricular cavity. The latter mode of secretion forms a particular structure called Reissner’s fiber (RF). The functional significance of the SCO/RF complex is still discussed, in spite of a wide range of experimental data. Here we present new molecular and biological data favoring a putative morphogenetic activity of the SCO/RF complex. The glycoproteins secreted by the SCO exhibit sequence homologies with proteins expressed in the developing nervous system, including thrombospondins 1 and 2, semaphorins F and G and F-spondin. These glycoproteins were called SCO-spondin because of their high expression in the SCO and the presence of conserved domains (thrombospondin type 1 repeats). Molecules exhibiting such domains have been shown to interfere with cell adhesivity and neuritic outgrowth. Besides the molecular features, we analyzed the biological effect of RF and solubilized material from RF on neuronal cells in primary cell cultures. In these in vitro systems, RF markedly enhanced cell survival and interfered with cell aggregation and neuritic outgrowth. Thus, both molecular and functional data give new insights into a putative morphogenetic activity of the SCO/RF complex.