Complementary patterns of Sema7A and plexinC1 expression in the olfactory system. In situ hybridization for Sema7A and plexinC1 on consecutive horizontal (A-H) and sagittal (I-L) sections of the primary and accessory olfactory system. Caudal is to the top in A and B, and to the right in C-L. (A, B) During embryonic (not shown) and postnatal development, Sema7A and plexinC1 are expressed throughout the apical (a) and basal (b) layers of the olfactory epithelium (OE). No expression is found in the lamina propria (lp) and septum (s). (C-H) Panels E and F show P15 non-septal (ns) OE and represent higher magnifications of the boxed areas in C and D. Panels G and H show P15 septal OE and represent higher magnifications of the boxed areas in C and D. As postnatal development progresses, Sema7A signals in the OE increase whereas weak expression of plexinC1 is found throughout the apical (a) and basal (b) layers of the OE. (D, F) Note, however, the moderate-to-strong plexinC1 signals in cells in the basal part of a specific patch of OE (arrows in D and F). (I, J) At E19, Sema7A is expressed in the mitral (m) and granule cell (gcl) layers of the olfactory bulb (OB). In addition, low levels of Sema7A can be detected in the accessory olfactory bulb (AOB). PlexinC1 is expressed by a subset of granule and mitral cells. Strong plexinC1 expression is found in the AOB, rostral migratory stream (RMS) and subventricular zone (SVZ). (K, L) At P15, Sema7A and plexinC1 are expressed in mitral, tufted, granule and periglomerular cells. gl, glomerular layer. Scale bar 40 μm (A, B), 460 μm (C, D), 105 μm (E-H), 500 μm (I, J), and 775 μm (K, L).