Accepted post-doctoral position at MIT after receiving PhD
Now a scientist at Agencourt Bioscience
Extracellular signals regulate fungal development and, to sense and respond to these cues, fungi evolved signal transduction pathways similar to those in mammalian systems. In fungi, heterotrimeric G proteins, composed of α, β, and γ subunits, transduce many signals, such as pheromones and nutrients, intracellularly to alter adenylyl cyclase and MAPK cascades activity.
Previously, the Gα proteins GNA-1 and GNA-2 were characterized in regulating development in the fungus Neurospora crassa. R.A. Baasiri isolated a third Gα, gna-3, and P.S. Rowley generated Dgna-3 mutants. GNA-3 belongs to a fungal Gα family that regulates cAMP metabolism and virulence. The Δgna-3 sexual cycle is defective in homozygous crosses, producing inviable spores. Δgna-3 mutants have reduced aerial hyphae formation and derepressed asexual sporulation (conidiation), causing accumulation of asexual spores (conidia). These defects are similar to an adenylyl cyclase mutant, cr-1; cAMP supplementation suppressed Δgna-3 and cr-1. Inappropriate conidiation and expression of a conidiation gene, con-10, were higher in Dgna-3 than cr-1 submerged cultures; peptone suppressed conidiation. Adenylyl cyclase activity and expression demonstrated that GNA-3 regulates enzyme levels.
A Dgna-1 cr-1 was analyzed with F. D. Ivey to differentiate GNA-1 roles in cAMP-dependent and -independent pathways. Δgna-1 cr-1 defects were worse than cr-1 and refractory to cAMP, suggesting that GNA-1 is necessary for sensing extracellular cAMP. Submerged culture conidiation was highest in Δgna-1 cr-1, and only high cell density Dgna-1 cultures conidiated, which correlated with con-10levels. Transcription of a putative heat shock cognate protein was highest in Δgna-1 cr-1.
Functional relationships between the three Gas was analyzed by constructing Δgna-1 Δgna-2 Δgna-3, Δgna-1 Δgna-3, and Δgna-2 Δgna-3 strains. Δgna-2 Δgna-3 strains exhibited intensified Δgna-3 phenotypes; Δgna-1 Δgna-2 Δgna-3 and Δgna-1 Dgna-3 strains were identical to Dgna-1 cr-1 on plates and were non-responsive to cAMP. The highest levels of conidiation and con-10 were detected in submerged cultures of Δgna-1 Δgna-2 Δgna-3 and Δgna-1 Δgna-3 mutants, which was partially suppressed by peptone supplementation. Stimulation of adenylyl cyclase is completely deficient in Δgna-1 Δgna-2 Δgna-3 and Δgna-1 Δgna-3 strains. Δgna-3 and Δgna-1 Δgna-3 aerial hyphae and conidiation defects were suppressed by mutation of a PKA regulatory subunit.
Functional Analysis of the Gα Protein, GNA-3, in the Development of Neurospora crassa Using Biochemical and Genetic Studies