Aspergillus nidulans hyphae grow by tip extension, and are later divided by crosswalls into actively growing tip and quiescent basal cells. Basal cells can branch, resuming growth after forming a new tip. Apical growth in tip cells, and growth arrest in basal cells, depend on the function of hypercellular genes, identified using temperature sensitive mutants. All hyp is strains can complete their asexual life cycle at 42Â°C and produce viable conidia, suggesting that these genes are not essential. Intriguingly, if hypA or hypB function is perturbed by shifting 28Â°C-grown germlings to 42Â°C, basal cells are remodeled to assume the restrictive phenotype, but tip cells die. For hypA, only, tip cell survival appears to be related to cell cycle stage. About 20% of control tips survive upshift, and this is increased three-fold by treatment with hydroxyurea. These results suggest that hypA is a nuclear-cycle related growth switch for hyphal development. hypA has sequence similarity to genes in budding and fission yeasts, and a cosmid containing the fission yeast ortholog was able to complement the hypA defect. Current efforts focus on defining the upshift phenotypes and proving homology between the A. nidulans hypA, and the yeast genes.
Fungal Genet. Newsl. 46 (Supl):
Full conference title:
Fungal Genetics Conference 20th
- Fungal Genetics Conference 20th (1999)