Figure 1.

Early and late activation of erbB2 after axotomy. A, Late activation of erbB2. Rat sciatic nerve was transected. At times indicated, the distal stumps were harvested. Nerve lysates were immunoprecipitated with antibodies to erbB2, size fractionated by SDS gel electrophoresis, and immunoblotted with antibodies to p-Tyr or erbB2. As reported previously (Carroll et al., 1997; Kwon et al., 1997), erbB2 protein is overexpressed and also activated at late stages of Wallerian degeneration (3-14 d) at times when Schwann cells have begun to proliferate. IP, Immunoprecipitation; WB, Western blot. B, Early activation of erbB2 (as above, except the nerve stumps were sampled on a timescale of minutes rather than days). As indicated, erbB2 is activated quickly (within 10 min) in the distal stump but not in the proximal stump of axotomized nerves. Activation is maximal between 30 and 60 min after axotomy and is then attenuated. The experiment shown is representative of four replicate experiments. The apparent increase in total erbB seen here at early times in the distal stumps is attributable to experimental variation and is not seen in other experiments. C, Early activation of erbB2 is selective. Nerve lysates from uncut and 1 h postaxotomized distal nerves were immunoprecipitated with erbB2 or PDGFβR antibodies and immunoblotted with p-Tyr antibody. The blots were reused and immunoblotted with erbB2 or PDGFβR antibodies. D, The neuregulin coreceptor erbB3 participates in the early activation response. Nerve lysates were immunoprecipitated with anti-erbB2 or anti-erbB3 and immunoblotted with antibodies to p-Tyr, erbB2, or erbB3, as indicated. As shown, both erbB2 and erbB3 are activated after nerve injury in the distal stump. E, Activation of MAPK in distal stumps after axotomy.