We have continued our characterization of
mig-10 mutant defects using a
ceh-23-gfp reporter strain (kyIs5 IV, kindly provided by Jennifer Zallen) which allows scoring of CAN cell bodies and axons (see Manser et al. WCWM 1998 abstracts, p.167). In the current studies, we have focused on the amber (putative null)
mig-10(
ct41) allele. Nearly 90% of CAN cell bodies (61/68) are significantly displaced anteriorward in
mig-10(
ct41);kyIs5 animals, compared to less than 8% (5/64) for the kyIs5 strain. Manser and Wood (1990) previously reported a penetrance of 60% for CAN cell body misplacement in
mig-10(
ct41). The higher penetrance observed using the gfp reporter probably reflects a synergy between
mig-10 and
ceh-23-gfp similar to that reported by Forrester et al. (1997) for other CAN migration mutants. A significant percentage of posteriorly directed CAN axons in
mig-10(
ct41);kyIs5 animals (23/67) terminate in positions significantly anterior to their normal target region near the anus. In contrast, all anteriorly directed CAN axons appear to extend to their normal target region in the head. This apparent directional bias is somewhat surprising given that
mig-10(
ct41) disrupts both anteriorward and posteriorward cell body migrations (Manser and Wood, 1990). One possibility is that the CAN axon defects are an indirect result of the shortening of the posterior excretory canals observed in
mig-10(
ct41) (Manser and Wood, 1990). Specifically, because CAN axons are closely associated anatomically with the excretory canals (CAN=canal associated neuron), perhaps the canals serve as guidance cues for axon outgrowth. To investigate this possibility, we have scored both CAN axon and posterior excretory canal defects in the same individuals. In more than 90% of
mig-10(
ct41);kyIs5 animals scored (28/31), the posteriorly directed CAN axon extended significantly beyond the point of termination of the posterior excretory canal. This set includes animals in which the posterior CAN axon extends to the anal region while the posterior excretory canal terminates significantly anterior to the vulval region. Due to the generally severe truncation of the posterior canals caused by
mig-10(
ct41), we have also observed animals in which the CAN cell body is positioned posterior to the canal terminus. In such animals, anteriorly directed CAN axons were observed to extend over regions of the anterior-posterior axis from which canals were missing. These observations do not support the view that the excretory canals serve as guidance cues for CAN axon outgrowth.