Polarized expression of integrin β1 in diencephalic roof plate during chick development, a possible receptor for SCO‐spondin

Abstract

The roof plate of the caudal diencephalon is formed by the posterior commissure (PC) and the underlying secretory ependyma, the subcommissural organ (SCO). The SCO is composed by radial glial cells bearing processes that cross the PC and attach to the meningeal basement membrane. Since early development, the SCO synthesizes SCO-spondin, a glycoprotein that shares similarities to axonal guidance proteins. In vitro, SCO-spondin promotes neuritic outgrowth through a mechanism mediated by integrin ␤1. However, the secretion of SCO-spondin toward the extracellular matrix that surrounds the PC axons and the expression of integrins throughout PC development have not been addressed. Here we provide immunohistochemical evidence to suggest that during chick development SCO cells secrete SCO-spondin through their basal domain, where it is deposited into the extracellular matrix in close contact with axons of the PC that express integrin ␤1. Our results suggest that SCO-spondin has a role in the development of the PC through its interaction with integrin ␤1.

Subdivisions of chick diencephalic roof plate: Implication in the formation of the posterior commissure

“…The study was made at stage HH26 ( Fig. 2A-A 0 ) when, as we previously described, the first axons of the PC begin to bundle (Caprile et al, 2009) and also at later stages (HH32; Fig. 2B-B 0 ), when the PC is well developed and its axons are highly fasciculated.…”

“…SCO is composed of radial glial cells with their apical domain facing the third ventricle and, hence, contacting the cerebrospinal fluid, whereas their basal domains extend prolongations that cross the nerve bundles of the PC and are attached to the pial membrane (Caprile et al, 2009). (2) In the chick, SCO differentiation occurs at HH17-18, concomitantly with the presence of the pioneer axons of the PC (Schoebitz et al, 1986;Didier et al, 2007;Caprile et al, 2009).…”

“…SCO is composed of radial glial cells with their apical domain facing the third ventricle and, hence, contacting the cerebrospinal fluid, whereas their basal domains extend prolongations that cross the nerve bundles of the PC and are attached to the pial membrane (Caprile et al, 2009). (2) In the chick, SCO differentiation occurs at HH17-18, concomitantly with the presence of the pioneer axons of the PC (Schoebitz et al, 1986;Didier et al, 2007;Caprile et al, 2009). (3) Mutations in genes that regulate the development of prosomere 1 display a wide range of abnormalities in the development of the SCO that are highly similar to the phenotypes observed in the PC (Schwarz et al, 1999;Estivil-Torrus et al, 2001;Fernandez-Llebrez et al, 2004;Ramos et al, 2004).…”

“…In the chick, pioneer axons that form the PC cross the midline at stage HH18 and, as development proceeds, fibers from diverse pretectal nuclei join these intrepid axons and the process of fasciculation occurs. (Puelles and Rubinstein, 2003;Caprile et al, 2009;Hoyo-Becerra et al, 2010).…”

“…(5) Peptides containing the TSR motifs of SCO-spondin interfere, by a mechanism mediated by integrin b1, with a variety of neuronal processes in vitro, including neuronal survival and neurite outgrowth (Gobron et al, 1996(Gobron et al, , 2000Monnerie et al, 1998;Meiniel, 2001;Meiniel et al, 2003;Bamdad et al, 2004). (6) SCO-spondin is basally secreted to the extracellular matrix, where it is in close contact with axons of the PC that express integrin b1 (Caprile et al, 2009).…”