An F-actin-depleted zone is present at the hyphal tip of invasive hyphae of Neurospora crassa

Abstract

The distribution of filamentous actin (F-actin) in invasive and noninvasive hyphae of the ascomycete Neurospora crassa was investigated. Eighty six percent of noninvasive hyphae had F-actin in the tip region compared to only 9% of invasive hyphae. The remaining 91% of the invasive hyphae had no obvious tip high concentration of F-actin staining; instead they had an F-actin-depleted zone in this region, although some F-actin, possibly associated with the Spitzenkörper, remained at the tip. The size of the F-actin-depleted zone in invasive hyphae increased with an increase in agar concentration. The membrane stain FM 4-64 reveals a slightly larger accumulation of vesicles at the tips of invasive hyphae relative to noninvasive hyphae, although this difference is unlikely to be sufficient to account for the exclusion of F-actin from the depleted zone. Antibodies raised against the actin filament-severing protein cofilin from both yeast and human cells localize to the tips of invasive hyphae. The human cofilin antibody shows a more random distribution in noninvasive hyphae locating primarily at the hyphal periphery but with some diffuse cytoplasmic staining. This antibody also identifies a single band at 21 kDa in immunoblots of whole hyphal fractions. These data suggest that a protein with epitopic similarity to cofilin may function in F-actin dynamics that underlie invasive growth. The F-actin-depleted zone may play a role in the regulation of tip yielding to turgor pressure, thus increasing the protrusive force necessary for invasive growth.

Intracellular mechanisms of fungal space searching in microenvironments

“…Similarly to nestling, the role of actin in the hit & split branching remains to be established by further experimentation. However, as it was shown, for two yeast species, 65 and for Neurospora crassa, 66 that actin is not present at the tip of invasive hyphae, i.e., those pressing against agar, i.e., in conditions similar to our experiments (Supplementary Movie SI 08 and SI 09). Consequently, it is expected that the contribution of actin is minimal to hit & split branching.…”

F-Actin Dynamics in Neurospora crassa

“…1; also see Fig. 5) and displayed a localization pattern of F-actin consistent with previous studies of N. crassa using immunofluorescent labeling (7,22,54,59). Latrunculin A treatment, which disrupts the actin cytoskeleton, confirmed F-actin labeling (see below).…”

“…Immunofluorescence studies of N. crassa have shown that F-actin localizes to hyphal tips as "clouds" and "plaques" (7,54,59). However, immunolabeling has failed to reveal actin cables in N. crassa and offers limited insights into F-actin dynamics.…”

Phytophthora capsici homologue of the cell cycle regulator SDA1 is required for sporangial morphology, mycelial growth and plant infection

“…Management of the cytoskeleton and the cell division cycle are key mechanisms required to address these challenges. Thus, the SDA1 protein, which has been identified in S. cerevisiae (Buscemi et al ., ) and human cells (Babbio et al ., ) as an important regulator of the actin cytoskeleton and also of the cell division cycle, is potentially a key player in the regulation of the growth and morphology of filamentous organisms, such as fungi (Berepiki et al ., ; Suei and Garrill, ) and oomycetes (Ketelaar et al ., ; Meijer et al ., ). However, to date, there have been no studies of this protein outside S. cerevisiae and human cells.…”

“…a1, silenced line SiPcSDA1-3; b1, overexpression line OPcSDA1-1; c, CK (empty vector transformant); d, wild-type strain SD33. and human cells (Babbio et al, 2004) as an important regulator of the actin cytoskeleton and also of the cell division cycle, is potentially a key player in the regulation of the growth and morphology of filamentous organisms, such as fungi (Berepiki et al, 2011;Suei and Garrill, 2008) and oomycetes (Ketelaar et al, 2012;Meijer et al, 2014). However, to date, there have been no studies of this protein outside S. cerevisiae and human cells.…”