Figure 4.

Components of the hyphal apex involved in orientation of the growth axis. Directionality involves calcium signalling through the Mid1–Cch1 channel complex, GTP–GDP cycling of the Ras-GTPase, Rsr1, delivery of specific cargo by kinesin motor proteins and proteins that tether microtubule plus ends to complexes in the apical sterol-rich domain. The Spitzenkörper is a vesicle assemblage fed by cytoplasmic transport of vesicles along microtubules which are tethered by via cell-end marker proteins. Vesicles finally are delivered to the membrane in the apex via actinomyosin. The spatial localisation of the KipA kinesin and Tea cell-end proteins in A. nidulans is shown along with the meandering mutant phenotypes of hyphae lacking these proteins (from R Fischer, with permission from Blackwell).