Expression of Sema6A, PlxnA2 and PlxnA4 in the caudal medulla. (a-i) In situ hybridization for Sema6A (a, d, g), PlxnA2 (b, e, h) and PlxnA4 (c, f, i) on coronal sections of the caudal medulla at P4. Sema6A and PlxnA4 are strongly expressed in the inferior olives in a partly complementary fashion (compare (a, d) with (c, f)). PlxnA2 is weakly expressed at this age in the inferior olives, in a pattern similar to PlxnA4 (b, e). Close to the level of decussation, all three molecules are expressed in the caudal portions of the inferior olive (io) (g-i). CST, corticospinal tract; ioa, b, c, subnuclei A, B, C of the medial nucleus of the inferior olive; iod, dorsal nucleus; iom, medial nucleus; iodm, dorsomedial cell group; iop, principal nucleus. Scale bar in (i) is 200 μm and is for (a-c, g-i); scale bar in (f) is 100 μm and is for (d-f).