Dynein's cargoes include the wingless and runt mRNAs, which concentrate at the apical tip of fly embryos. Delanoue and Davis found that agents that disrupt microtubule function caused the mRNAs to disperse. Injection of antibodies against dynein subunits disrupted localization of both injected exogenous RNAs and endogenous transcripts, indicating that dynein itself was doing the anchoring.To distinguish between static anchoring and continuous localization, the team used a two-step injection design. They injected one batch of labeled RNA, allowed it to localize, and then injected a second batch along with an ATPase inhibitor to block dynein motility. Under these conditions, the previously localized RNA stayed put, while the newly injected RNA failed to localize. The team thus concluded that dynein remains with its cargo and anchors it at the target site.
“We'd like to think the use of a motor for anchoring is a general mechanism both in terms of other cargoes and other motors,” says Davis. “There could be a whole range of transport and anchoring mechanisms involving different motors.” He points out that motors are abundant in most cells and could provide a convenient tether after transport.