Tip growth of Neurospora crassa

The filamentous fungus Neurospora crassa is a popular experimental model organism. The defining characteristic of filamentous fungi is the development of hyphae, tip-growing tubular branching structure. Tip growth of N. crassa has been studied intensively for over some tens years. It is clear now that the tip-growing hyphae can use the biosynthetic resources of many tens and hundreds of microns of hyphal trunk to drive forward the apex. Cell-wall biosynthesis and cell extension are located at the apical region and the membrane and enzymes required to expand the apex are packaged in microvesicles that are translocated through the hypha to apex via actin microfilaments and microtubules. Secretory vesicles then fuse with the tip to deliver membrane and materials required for the continuous cell-wall synthesis. This is thought to be coordinated by the Schpitzencorper, a fungal specific organelle, which is localized in the hyphal apex and serves as a vesicle-supply center. A lot of molecular and genetic aspects of the tip growth have become clear now, especially those concerning the activity of chitin synthesis, molecular motors and signal transduction systems. Electrophysiological studies of N. crassa indicate membrane polarization, pH- and Ca2(+)-gradients and electrical currents at the growing apex. Some theories based on the mathematical modeling and computer simulation approaches attempt to account for various aspects of tip growth. The genome sequence of N. crassa was recently reported. Thus, the next few years should clarify the problem of the hyphal growth and integrate the whole basis of physiological, cytological and molecular biology details into a generally accepted picture.