Semaphorins and neuropilins affect the migration of the Gonoadotropin Releasing Hormone (GnRH)-secreting neurons

AIM: Reproduction in mammals is centrally regulated by neurons secreting GnRH, which, during development, originate in the nasal compartment and migrate along the olfactory nerves to reach their final destinations in the hypothalamus. The molecular mechanisms directing GnRH-neuron migration are not completely understood. In this study, we aimed to investigate the role of secreted class 3 semaphorins (Sema3A, 3F) and neuropilins (NP-1, NP-2) on the migration of GnRH neurons, due to their expression in the olfactory system and to the reproductive problems reported in NP-2 null mice. METHODS: Analysis of GnRH-neurons complement in NP-2 null mice as well as expression studies on both immortalized GnRH-neurons (GN11 cell-line) and rodents have been performed using immunohystochemistry and RT-PCR. GFP-GnRH mice have been used in combination with FACS technique and RT-PCR. Boyden’s chamber and collagen gels were used as chemomigration tests. RESULTS: Analysis of P0 NP-2 mice showed a significant reduction in number of GnRH-neurons in the forebrain compared to WT littermates. Immunostaining of olfactory fibres for peripherin, a specific axonal marker, showed severe defasciculation, suggesting an indirect role of NP-2 on migration of GnRH neurons. However using FACS and RT-PCR on GFP-GnRH cells, we showed expression of Sema3A, 3F, NP-1, NP- 2 in these cells. Same pattern of expression was confirmed in GN11 cells, of which chemomigration is inhibited by Sema 3A and 3F. CONCLUSIONS: These data suggest that semaphorins and neuropilins both intervene to control GnRH-neuron migration as well as fasciculation of the olfactory nerves, and implicate the possibility of a mutual influence between these two systems.