Fig. 9. HB-EGF-induced autophosphorylation of ErbB1 (A) and ErbB4 (B) in day 4 uteri and blastocysts of hamsters. Autophosphorylation of ErbBs was determined in uterine membrane and blastocyst homogenate after preincubation (10 minutes) with or without HB-EGF (4 ng/ml, human recombinant HB-EGF; a gift from Dr M. Klagsbrun, Harvard medical School, Boston, MA). Day 4 mouse uterine membranes were used as controls. The labeling reaction was initiated by the addition of [-³²P]ATP for 2 minutes. After labeling, proteins were precipitated with 10% trichloroacetic acid. The precipitates were then used for immunoprecipatation with antibodies to ErbB1 and ErbB4. The immunoprecipates were separated by SDS-PAGE (6%), and phosphorylated proteins were detected by autoradiography. No growth factor was added to the samples in lanes 1, 3 and 5. HB-EGF was added to those in lanes 2, 4 and 6. Lanes 1 and 2 show hamster uterine membranes; lanes 3 and 4 show day 4 mouse uterine membranes; lanes 5 and 6 show hamster blastocyst homogenates. These experiments were performed twice.