Self-organization of intracellular structures in the apical segment of growing Neurospora crassa hyphae

Tatiana Belozerskaya 1 Tatiana Potapova 2
1Ecological and Evolutionary Biochemistry, Research Center of Biotechnology, RAS; Bach Institute of Biochemistry, Moscow, Russia
2Mathematical Methods in Biology, Moscow Lomonosov State University, Belozersky Institute of Physico-chemical Biology, Moscow, Russia

N.crassa hyphae grow by apical extention at rates of about 20-30 μm/min forming lateral branches. Hypha consists of segments 10-20 μm in diameter and 50-100 μm length, each containing about 20-30 nuclei 2-3 μm in diameter, asynchronously dividing every 80-90 min. Plasma membrane and the cell wall are permanently formed de novo at the hyphal apex with the participation of endoplasmic reticulum, Golgi apparatus, actin cytoskeleton, microtubuls, and mitochondria. All these structures are located in the apical segment in a well-defined order which arises de novo during conidia outgrowth or lateral branch development. This order is supported constantly during apical growth. A detailed description is needed to evaluate the role of morphogens, forces or fields which create and support the mentioned order and to unravel communicative mechanisms of its players. An integral part of apical development is lack of H+-ATPases, the main membrane potential generators, in the hyphal apices (~100 μm from the tip) The result of such intrahyphal segregation is creation of a profound local electric field-(~100 V/m), and an electric current generation comparable in magnitude with a proton pump current. We have shown that growth rate of isolated hyphal apices decreased, the diameter narrowed, and their lateral branching was inhibited, but the length of the apical segment (150 — 300 μm) did not change as well as the intercalary one (50 — 100 μm). Molecular detailes of hyphal septation are well documented. Unfortunately they can’t provide understanding of what kind of sources and fields determine the length of a hyphal segment and keep the first septum at a distance of 150-300 μm from the apex. Mechanisms of apical growth control by the nuclei are also not yet clear.