Supplementary Components01. and demonstrate that coincidence signaling between CR cell-derived secreted and short-range guidance-cues direct neuronal migration. INTRODUCTION Developmental processes frequently depend on transient cell populations to guide migrating cells. One such population in the CNS are the Cajal-Retzius (CR) cells, which have crucial functions in the developing neocortex and hippocampus (Soriano and Del Ro, 2005). In the neocortex, CR cells Panaxtriol reside in the marginal zone (MZ) and secrete reelin, which signals to projection neurons to control their radial migration (Franco et al., 2011; Gupta et al., 2003; Jossin and Cooper, 2011; Olson et al., 2006; Sekine et al., 2011). At early stages of neocortical development, radially migrating neurons enter the cortical plate (CP) using a migration mode called glia-independent somal translocation, which is characterized by the movement of neuronal cell bodies along their Panaxtriol leading processes that are located in the marginal zone (MZ) (Nadarajah et al., 2001; Tabata and Nakajima, 2003). Later-born neurons must migrate further and thus use several modes of migration (Noctor et al., 2004; Tabata and Nakajima, 2003), but ultimately complete their migration by switching to glia-independent somal translocation MYCC once their leading processes enter the MZ (Nadarajah et al., 2001). Reelin specifically regulates glia-independent somal translocation in early- and late-born neurons (Franco et al., 2011), but is dispensable for other modes of motility (Franco et al., 2011; Jossin and Cooper, 2011). During glia-independent somal translocation, reelin regulates the activity of cadherin 2 (Cdh2) to maintain neuronal leading processes in the MZ (Franco et al., 2011), possibly through their interaction with CR cells. Cdh2 is widely expressed in radial glial cells (RGCs) and neurons of the developing neocortex and is critical for a variety of cellular processes. In migrating neurons, Cdh2 is not only required for forming stable attachments to cell in the MZ (Franco et al., 2011), but also for establishing dynamic adhesions with RGCs during glia-dependent migration (Kawauchi et al., 2010). In contrast, Cdh2 forms stable adherens junctions between RGCs at the ventricular surface (Kadowaki et al., 2007; Rasin et al., 2007). We therefore hypothesized that migrating neurons and other neocortical cell types, such as RGCs and CR cells, might express additional cell surface receptors that direct the specificity of the homophilic cell adhesion molecule Cdh2 towards establishment of heterotypic cell-cell contacts with distinct functional properties. Candidate molecules for such interactions are the nectins, a branch of the immunoglobulin superfamily that consists of four members (Takai et al., 2008). Outside the nervous system, nectins cooperate with cadherins in the assembly of adherens junctions (Takahashi et al., 1999; Takai et al., 2008). Within the nervous system, nectins have important functions at synaptic sites (Rikitake et al., 2012). Importantly, some nectins, such as nectin1 and nectin3, preferentially engage in heterophilic interactions that play crucial roles during development (Honda et al., 2006; Inagaki et al., 2005; Okabe et al., 2004; Rikitake et al., 2012; Togashi et al., 2011; 2006). Panaxtriol However, the functions of nectins in the developing neocortex are not known. Here we show that nectin1 and nectin3 are expressed in complementary patterns in the neocortex, in which radially migrating neurons express nectin3 and CR cells express nectin1. We demonstrate that nectin1 in CR cells mediates heterotypic interactions with nectin3 in the leading processes of migrating projection neurons. These nectin-based adhesions control radial migration by acting in concert with reelin and Cdh2 to promote connections between migrating neurons and CR cells. General, our results reveal that CR cells instruct the directional migration of neocortical projection neurons by coincident display of secreted substances, such as for example reelin, and cell-surface destined guidance cues, such as for example nectins and cadherins. Our outcomes clarify the way the homophilic cell adhesion molecule Cdh2 also, which is Panaxtriol portrayed in lots of neocortical cell types, mediates particular connections between two described cell types by combinatorial signaling with various other cell adhesion substances. RESULTS Nectin appearance in the developing neocortex Prior studies show that nectins cooperate with cadherins in adherens junction set up (Takahashi et al., 1999; Takai Panaxtriol et al., 2008). Since Cdh2 regulates radial neuronal migration (Franco et al., 2011; Jossin and Cooper, 2011; Kawauchi et al., 2010), we hypothesized that nectins may.