PlexinA1 interacts with PTK7 and is required for neural crest migration Gabriele Wagner a,b,1 , Hanna Peradziryi a,1 , Peter Wehner a , Annette Borchers a,⇑ a Department of Developmental Biochemistry, Center for Molecular Physiology of the Brain (CMPB), GZMB, University of Göttingen, Justus-von-Liebig-Weg 11, 37077 Göttingen, Germany b Adolf-Butenandt-Institute, Ludwig-Maximilians-University Munich, Schillerstrasse 44, D-80336 Munich, Germany article info Article history: Received 7 October 2010 Available online 12 October 2010 Keywords: Plexin Xenopus Neural crest migration PTK7 abstract Members of the plexin protein family are known regulators of axon guidance, but recent data indicate that they have broader functions in the regulation of embryonic morphogenesis. Here we provide further evidence of this by showing that PlexinA1 is expressed in Xenopus neural crest cells and is required for their migration. PlexinA1 expression is detected in migrating cranial neural crest cells and knockdown of PlexinA1 expression using Morpholino oligonucleotides inhibits neural crest migration. PlexinA1 likely affects neural crest migration by interaction with PTK7, a regulator of planar cell polarity that is required for neural crest migration. PlexinA1 and PTK7 interact in immunoprecipitation assays and show pheno- typic interaction in co-injection experiments. Considering that plexins and PTK7 have been shown to genetically interact in Drosophila axon guidance and chick cardiac morphogenesis, our data suggest that this interaction is evolutionary conserved and may be relevant for a broad range of morphogenetic events including the migration of neural crest cells in Xenopus laevis. Ó 2010 Elsevier Inc. All rights reserved. 1. Introduction Plexins are single-pass transmembrane receptors for semapho- rin guidance cues that control cell shape, cell–cell interactions and cell motility. Plexins were originally identified by their expression in the plexiform layers of the Xenopus tadpole nervous system [1] and were later shown to function as receptors for axon guidance cues of the semaphorin family [2,3]. From their initial characteriza- tion in repulsive axon guidance, semaphorins and their plexin receptors are now appreciated as major regulators of morphogen- esis and homeostasis [4,5]. They control processes like epidermal, vascular or cardiac morphogenesis [6–8], but have also been impli- cated in immune cell regulation, tumor progression or neurode- generative diseases [9]. Consistent with their broad range of functions plexins and sem- aphorins comprise large families of evolutionary conserved pro- teins. Based on their structural homology semaphorins have been grouped into eight classes (1–8) that are complemented by four categories (A–D) of plexin receptors [10]. Structurally plexins are large single-pass transmembrane molecules with conserved extra- cellular motifs, like the ß-propeller sema domain, the cysteine-rich MET-related sequences, and the immunoglobuline-like domains shared by plexins and transcription factors (IPT domains) [11,12]. The intracellular domain shares homology with the GAP domain of p120 RasGAP and directly stimulates the intrinsic guanosine tri- phosphatase (GTPase) activity of R-Ras [13]. As this domain inter- acts with several intracellular signaling transducers, including the Rho GTPases Rnd1 and Rac1, multiple signaling pathways involved in the regulation of cell adhesion and cytoskeletal arrangement can be affected by plexin signaling [10]. The pleiotropic signaling outcome of the plexin receptor com- plex may in part be modulated by the choice of co-receptors. PTK7 (protein tyrosine kinase 7) is a transmembrane receptor with no associated kinase activity [14], that can function as a plexin co-receptor. During chick cardiac morphogenesis, PlexinA1 can either form a receptor complex with PTK7 or VEGFR2 (vascular endothelial growth factor receptor type 2) and, depending on the choice of co-receptor, promote or inhibit cell migration in response to sema6D [15]. The plexin-PTK7 interaction also plays a role in Drosophila axonal guidance. The Drosophila ortholog of PTK7, off track (otk), interacts molecular and genetically with PlexinA and is important for Sema1a repulsive signaling [16]. As otk can inter- act with Drosophila and mammalian members of the plexin family [16], the plexin-PTK7 interaction is likely evolutionary conserved. Previously, we have demonstrated that PTK7 is a regulator of pla- nar cell polarity that regulates neural crest (NC) migration [17,18], suggesting that a plexin-PTK7 interaction may also play a role in this process. NC cells are induced at the border region of the neural plate and migrate on defined routes throughout the embryo, where they give rise to a variety of derivatives ranging from neurons and glia cells of the peripheral nervous system to cartilage and pigment cells. Recent evidence indicates that semaphorins function as guidance 0006-291X/$ - see front matter Ó 2010 Elsevier Inc. All rights reserved. doi:10.1016/j.bbrc.2010.10.044 ⇑ Corresponding author. Fax: +49 551 3915614. E-mail address: annette.borchers@gmail.com (A. Borchers). 1 These authors contributed equally. Biochemical and Biophysical Research Communications 402 (2010) 402–407 Contents lists available at ScienceDirect Biochemical and Biophysical Research Communications journal homepage: www.elsevier.com/locate/ybbrc