CDB15:0001340 SEMA3A — NRP1

ABSTRACT: The class 3 Semaphorins Sema3A and Sema3F are potent axonal repellents that cause repulsion by binding Neuropilin-1 and Neuropilin-2, respectively. Plexins are implicated as signaling coreceptors for the Neuropilins, but the identity of the Plexins that transduce Sema3A and Sema3F responses in vivo is uncertain. Here, we show that Plexin-A3 and -A4 are key determinants of these responses, through analysis of a Plexin-A3/Plexin-A4 double mutant mouse. Sensory and sympathetic neurons from the double mutant are insensitive to Sema3A and Sema3F in vitro, and defects in axonal projections in vivo correspond to those seen in Neuropilin-1 and -2 mutants. Interestingly, we found a differential requirement for these two Plexins: signaling via Neuropilin-1 is mediated principally by Plexin-A4, whereas signaling via Neuropilin-2 is mediated principally by Plexin-A3. Thus, Plexin-A3 and -A4 contribute to the specificity of axonal responses to class 3 Semaphorins.

ABSTRACT: Semaphorins are a large family of secreted and transmembrane proteins, several of which are implicated in repulsive axon guidance. Neuropilin (neuropilin-1) was recently identified as a receptor for Collapsin-1/Semaphorin III/D (Sema III). We report the identification of a related protein, neuropilin-2, whose mRNA is expressed by developing neurons in a pattern largely, though not completely, nonoverlapping with that of neuropilin-1. Unlike neuropilin-1, which binds with high affinity to the three structurally related semaphorins Sema III, Sema E, and Sema IV, neuropilin-2 shows high affinity binding only to Sema E and Sema IV, not Sema III. These results identify neuropilins as a family of receptors (or components of receptors) for at least one semaphorin subfamily. They also suggest that the specificity of action of different members of this subfamily may be determined by the complement of neuropilins expressed by responsive cells.