Expression pattern of sema A andsema IV in the developing head. Hybridizations were performed with 35S-labeled (A–D) or digoxigenin-labeled (E) riboprobes on coronal (A–D) and horizontal (E) sections of E15 rat brains. The prospective location of the LOT is delimited by dashes in A–C. A, B, sema A mRNA is found in the mesenchyme precursor of the frontal bone (A, arrows), immediately adjacent to the LOT. Expression starts at the base of the OB inA and runs caudally to the level of the trigeminal ganglion (V) that is also expressingsema A (see B). C, D,sema IV is expressed in the cortical plate (arrowheads) and in the ganglionic eminence (ge). Strong expression is also found in the choroid plexuses (cp) and the skin. Note inC and D that the septum (S) is not expressing sema IV. InE, sema IV expression is homogeneously high in the olfactory epithelium (arrowheads). Scale bars: A, 215 μm; B, D, 110 μm; C, 240 μm; E, and 300 μm.
