Distribution of plexin and neuropilin mRNAs in the cranium and brain stem of chick embryos

Semaphorins exert their effects in neuronal and non-neuronal processes by binding with receptors. Both in vitro and in vivo studies have shown that plexin-As (plexin-A1, plexin-A1 and plexin-A1) and neuropilins (Npn-1 and Npn-2) are the binding moieties for class-III semaphorins. These receptors are expressed in a spatially and temporally discontinuous manner during organogenesis and central nervous system (CNS) development in vertebrates. However, the signaling receptors that accompany with the class-III semaphorins to mediate their actions are still poorly characterized. To assess their diverse roles in neural circuit formation, we analyzed the expression patterns of plexin-A1, plexin-A2, plexin-A4, Npn-1 and Npn-2 in the head and brain stem of chick embryos. In developing eye, plexin-A1 expressed in the lens, whereas plexin-A2 and Npn-1 in the periorbital mesenchyme. Plexin-A1 also expressed throughout the otic vesicle but Npn-1 expressed only in the dorsal part. Among the analyzed plexins and neuropilins, only Npn-2 expression was detected in the branchial arches. Npn-2 and plexin-A4 were also expressed in the trigeminal and vago-accessory ganglia. In the hindbrain, all analyzed plexins and neuropilins were expressed by the selective sets of dorsal(dMNs) and ventral exiting motor neurons (vMNs) except plexin-A4 (only dMNs). Interestingly, plexin-A2 and Npn-1 were co-expressed by the similar sets of dMNs and vMNs (trochlear, trigeminal, abducens, glossopharyngeal, vago-accessory and hypoglossal nuclei). These expression findings suggest that plexins and neuropilins are involved in neurodevelopment of the cranial structures in chick embryos.