Semaphorins were first cloned as recognised mediators of cellular guidance, and consist of a large family of phylogenetically conserved secreted and transmembrane signalling proteins. Among the best-characterised vertebrate Semaphorins are the five secreted Class 3 members that contain an approximately 500 amino acid N-terminal Semaphorin domain, a C2 type immunoglobulin domain, and a highly basic C-terminal tail []. Two receptor families have been implicated in mediating the actions of class 3 semaphorins: the Neuropilins and Plexins. The nine known vertebrate Plexins are divided into four subfamilies (A through D) based on structure []. Several Plexins have been shown to interact directly with some class 4, 7 and V Semaphorins, but class 3 Semaphorins, however, do not appear to bind Plexins directly. Rather, the functional receptors for these Semaphorins are complexes of Neuropilins and A-type Plexins, with the former serving as the ligand-binding moiety and the latter the signal-transducing component [, ]. There are two Neuropilins (NP-1 and NP-2) that bind the five class 3 Semaphorins preferentially. In particular, Sema3A binds NP-1, whereas Sema3F utilises NP-2, while NP-1 and NP-2 heterodimers are thought to serve as functional receptors for Sema3C [].Semaphorin 4F may be involved in the injury response of intramedullary axotomized motoneurons [].
Semaphorins were first cloned as recognised mediators of cellular guidance, and consist of a large family of phylogenetically conserved secreted and transmembrane signalling proteins. Among the best-characterised vertebrate Semaphorins are the five secreted Class 3 members that contain an approximately 500 amino acid N-terminal Semaphorin domain, a C2 type immunoglobulin domain, and a highly basic C-terminal tail []. Two receptor families have been implicated in mediating the actions of class 3 semaphorins: the Neuropilins and Plexins. The nine known vertebrate Plexins are divided into four subfamilies (A through D) based on structure []. Several Plexins have been shown to interact directly with some class 4, 7 and V Semaphorins, but class 3 Semaphorins, however, do not appear to bind Plexins directly. Rather, the functional receptors for these Semaphorins are complexes of Neuropilins and A-type Plexins, with the former serving as the ligand-binding moiety and the latter the signal-transducing component [, ]. There are two Neuropilins (NP-1 and NP-2), which bind the five class 3 Semaphorins preferentially. In particular, Sema3A binds NP-1, whereas Sema3F utilises NP-2, while NP-1 and NP-2 heterodimers are thought to serve as functional receptors for Sema3C [].Recent work suggests a possible role of Gallus gallus (Chicken) Sema3E/collapsin-5 in restricting growth of retinal ganglion cell axons to the optic fibre layer [].
Semaphorins were first cloned as recognised mediators of cellular guidance, and consist of a large family of phylogenetically conserved secreted and transmembrane signalling proteins. Among the best-characterised vertebrate Semaphorins are the five secreted Class 3 members that contain an approximately 500 amino acid N-terminal Semaphorin domain, a C2 type immunoglobulin domain, and a highly basic C-terminal tail []. Two receptor families have been implicated in mediating the actions of class 3 semaphorins: the Neuropilins and Plexins. The nine known vertebrate Plexins are divided into four subfamilies (A through D) based on structure []. Several Plexins have been shown to interact directly with some class 4, 7 and V Semaphorins, but class 3 Semaphorins, however, do not appear to bind Plexins directly. Rather, the functional receptors for these Semaphorins are complexes of Neuropilins and A-type Plexins, with the former serving as the ligand-binding moiety and the latter the signal-transducing component [, ]. There are two Neuropilins (NP-1 and NP-2) that bind the five class 3 Semaphorins preferentially. In particular, Sema3A binds NP-1, whereas Sema3F utilises NP-2, while NP-1 and NP-2 heterodimers are thought to serve as functional receptors for Sema3C [].Recent microarray studies have suggested a role for Sema 6C in dental mesenchyme-induced neurite repulsion [].
