PMC:3191169 / 33749-37926 JSONTXT

{"project":"2_test","denotations":[{"id":"22022520-12124402-87377407","span":{"begin":319,"end":321},"obj":"12124402"},{"id":"22022520-15996548-87377408","span":{"begin":388,"end":390},"obj":"15996548"},{"id":"T18651","span":{"begin":319,"end":321},"obj":"12124402"},{"id":"T11050","span":{"begin":388,"end":390},"obj":"15996548"}],"text":"EphA7 modulates growth cone morphology yet is dispensable for ephrin-neurotrophin communication\nIn order to uncover a specific Eph receptor family member (EphA1-EphA8, EphB2) transducing ephrin-A5's impact on neurotrophin signaling, EphA7 was further analyzed (Fig. 7). EphA7 is expressed on hippocampal neurons (e.g. [59]) and EphA7 ablation results in aberrant axon guidance processes [15]. Therefore EphA7 might be potential candidate receptor for mediating ephrin-A5's influence on neurotrophin signaling in hippocampal neurons.\n10.1371/journal.pone.0026089.g007 Figure 7 EphA7 modulates growth cone morphology yet is dispensable for ephrin-neurotrophin communication.\nHippocampal neurons derived from wild-type (A, C) and EphA7 deficient mice (B, D) were stained for DAPI (blue), tubulin (green) and F-actin (red) expression. Individual growth cones in (A–D) are labeled by an arrow. (A–D) The area of individual growth cones of wild-type neurons (A; higher magnification in C) exceeds that of EphA7 deficient growth cones (B; higher magnification in D). Filopodia length and number was elevated in EphA7 deficient growth cones compared to control. (E) Quantification of growth cone area. Epha7 mutant growth cone area was reduced almost two-fold compared to wild-type. (F) The length of individual filopodia is increased in EphA7 deficient growth cones compared to wild-type. (G, H) The total number of filopodia/growth cone is increased in EphA7 deficient growth cones compared to control (G). (H) depicts the distribution (in percentage) of growth cones harboring a certain filopodia number (1-6 and \u003e6). The frequency of growth cones with 6 or more filopodia is almost doubled upon EphA7 deletion. (I) EphA7 is dispensable for transducing ephrin-A5 collapsing activity in hippocampal neurons. Addition of three concentrations of ephrin-A5 resulted in a comparable growth cone collapse induction in wild-type and EphA7 deficient neurons. (J) EphA7 is not required for ephrin-A mediated suppression of BDNF-evoked growth cone motility. In the absence of EphA7, ephrin-A5 and BDNF co-administration reduced the growth cone area (J), filopodia length and number (data not shown) elevated by BDNF alone. Scale-bar (A, B)  =  10 µm; (C, D)  =  5 µm. Hippocampal neurons derived from wild-type or EphA7 deficient mice were indistinguishable with regard to overall neurite length (data not shown). In contrast, growth cone morphology of Epha7 mutant neurons (arrows Fig. 7B, D) was altered compared to wild-type (arrows Fig. 7A, C). EphA7 deficient cultures were readily distinguishable from control cultures by the reduced overall area taken up by individual growth cones (Fig. 7E). Although overall growth cone area was reduced (Fig. 7E), filopodia length and number were increased upon EphA7 deletion (Fig. 7F–H).\nNext, sensitivity of Epha7 mutant neurons towards ephrin-A5 was tested in the growth cone collapse assay (Fig. 7I). Employing three different ephrin-A5 concentrations, we observed a full growth cone collapse response for both wild-type and EphA7 deficient neurons. This result suggests that EphA7 is not a crucial EphA receptor on hippocampal neurons for mediating ephrin-As repulsive guidance activity. Also, due to the promiscuity in Eph-ephrin interactions (see introduction) other Eph receptors expressed on hippocampal growth cones (e.g. EphA4, EphA5, EphA6, EphB2) might transduce ephrin-A5's collapsing activity.\nFinally we tested whether ephrin-A5 requires EphA7 to repress neurotrophin mediated neuronal motility (Fig. 7J). Similar to wild-type neurons, we observed that co-application of ephrin-A5 and BDNF in EphA7 deficient growth cones still resulted in a decrease of the growth cone area (Fig. 7J) as well as filopodia length and number (data not shown). This suggests that EphA7 is not required to transmit ephrin-A5's impact on neurotrophin signaling. As above, other Eph receptors are likely compensating for EphA7 deficiency or fulfill the major ephrin-A5 receptor function to interact with neurotrophin signaling.\nIn sum, EphA7 modulates growth cone morphology yet is dispensable as ephrin-A5 receptor to suppress neurotrophin signaling."}