Figure 10

Protein 4.1B is required to maintain a barrier at the para-axon initial segment (AIS) and to cluster voltage-gated potassium (Kv)1 channels. Triple immunostaining of ankyrin G (AnkG) (A), protein 4.1B (B) and Kv1.1 (C) in motor neurons (MNs) labeled with the anti-Peripherin antibody (data not shown) showing expression of protein 4.1B in the para-AIS, the juxtapara (JXP)-AIS and the internode. Triple immunostaining of AnkG (D, G, J), contactin-associated protein (Caspr) (E, H, K) and Kv1.1 (F, I, L) in MNs of wild-type (WT) (D-F) and 4.1B^-/- (G-L) mice showing an abnormal expression of Caspr and Kv1.1 in the para-AIS of 4.1B^-/- mice. Triple immunostaining of AnkG (M, P), PSD-93 (N) or Caspr2 (Q), and Kv1.1 (O, R) in MNs of 4.1B^-/- mice showing a similar abnormal expression of PSD-93, Caspr2 and Kv1.1 in the para-AIS. Brackets indicate protein 4.1B⁺ (A-C) and Caspr⁺ (D-L) domains. Scale bar = 5 μm. (S, T) The mean immunofluorescence intensity profile (shown by the line) ± SEM from n = 6 AISs is shown for AnkG, Caspr and Kv1.1 in WT (S) and 4.1B^-/- mice (T). Axon segments were aligned at the end of their AIS (dashed line). For each axon segment and each antibody, immunofluorescence intensities were normalized relative to its maximum intensity along that segment. (U) Mean (± SEM) length of AnkG and mean (± SEM) beginning and end positions of Caspr from n = 11 (soma-derived) AISs, aligned at the beginning of their AIS (dashed line), from WT and 4.1B^-/- mice.