Skip to Main Content
 

Global Search Box

 
 
 
 

Files

File List


ucin1128432277.pdf (2.8 MB)

ETD Abstract Container

Abstract Header

Aspergillus Fumigatus Ras Homologs Regulate Vegetative Growth, Development and Virulence

Fortwendel, Jarrod R.
http://rave.ohiolink.edu/etdc/view?acc_num=ucin1128432277

Abstract Details

2005, PhD, University of Cincinnati, Medicine : Pathobiology and Molecular Medicine.
Conidial germination and growth by apical extension are two processes required for the initiation and progression of disease by the opportunistic pathogen Aspergillus fumigatus. The Ras family of GTPase proteins has been shown to control morphogenesis in many organisms, including several species of pathogenic fungi. Therefore, we sought to determine the requirements for Ras proteins in conidial germination and hyphal develolpment of A. fumigatus. Previously, only one homolog, rasA, had been identified, but nothing is known of its role in growth and development. We have identified a second homolog, rasB, which characterizes a new subclass of Ras genes, found only in fungi that undergo hyphal growth. Unique to the rasB homologs is a conserved amino acid domain found just upstream of the third GTP/GDP binding region. To gain insight into the roles played by RasB in A. fumigatus, dominant active (DA), dominant negative (DN) and deletion mutations were constructed for both Ras homologs. DArasB expression led to reduced conidiation. Expression of DNrasB slightly delayed the initiation of germination and caused the development of conidiophores in submerged culture, an abnormal event in A. fumigatus. Deletion of A. fumigatus rasB caused decreased germination and growth rates but no significant change in total biomass after 24 hours of growth. Deletion of rasB also created an irregular hyphal morphology characterized by increased branching. Expression of rasBΔ113-135, a mutant lacking the conserved rasB internal amino acid insertion, did not complement the deletion phenotype. Virulence of the rasB deletion strain was also reduced, as mice infected with this strain exhibited ~70% survival compared to ~10% with wild type and reconstituted strains. In contrast, DArasA expression led to reduced conidiation, malformed conidiophores, and altered mitotic progression. Expression of DNrasA caused a significant reduction in the rate of conidial germination, without further altering development. However, complete deletion of rasA caused slowed germination, nearly absent radial outgrowth, and decreased hyphal mass. Although conidiation was reduced and delayed, the conidial viability was near wild type levels. The ΔrasA mutant was also resistant to protoplast preparation using normal levels of cell wall digestion enzymes. Normal mitotic events in the mutant were also disturbed, as staining of nuclear material revealed many small nuclei that were irregularly positioned throughout the hyphal compartments. RasA and RasB appear to play distinct, and overlapping, roles in the vegetative growth and asexual development of A. fumigatus. The data in this study, along with the fact that rasB homologs are highly conserved among fungi that undergo hyphal growth, also support the hypothesis that rasB may control signaling modules important to the directional growth of fungal hyphae.
Dr. Judith Rhodes (Advisor)
149 p.
Aspergillus; Ras; Fungus; Branching; Germination; Development; Virulence

Recommended Citations

Citations

  • Fortwendel, J. R. (2005). Aspergillus Fumigatus Ras Homologs Regulate Vegetative Growth, Development and Virulence [Doctoral dissertation, University of Cincinnati]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1128432277

    APA Style (7th edition)

  • Fortwendel, Jarrod. Aspergillus Fumigatus Ras Homologs Regulate Vegetative Growth, Development and Virulence. 2005. University of Cincinnati, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=ucin1128432277.

    MLA Style (8th edition)

  • Fortwendel, Jarrod. "Aspergillus Fumigatus Ras Homologs Regulate Vegetative Growth, Development and Virulence." Doctoral dissertation, University of Cincinnati, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1128432277

    Chicago Manual of Style (17th edition)

ucin1128432277
1,327
© 2005, all rights reserved.
This open access ETD is published by University of Cincinnati and OhioLINK.