Expression of Sema6A, PlxnA2 and PlxnA4 in the hindbrain. (a-f) In situ hybridization for Sema6A, PlxnA2 and PlxnA4 at P0–P1, in sagittal (a, c, e) and coronal (b, d, f) planes. Strong expression of Sema6A (a, b) is observed in the pontine nuclei (pn) and other structures close to the corticospinal tract (CST) at the level of the pons, including the pontine reticular nucleus (prt) and superior olive (so), as well as in the inferior olive (io). PlxnA2 (c, d) and PlxnA4 (e, f) are expressed in distinct but overlapping patterns in these structures. In the inferior olive, PlxnA2 expression could not be detected at this age (Figure 6). The dashed line in (c) shows the approximate level of coronal sections. Scale bar: 500 μm.