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RESEARCH
Proper growth of the fungal cell requires coordination of nuclear division,
cytokinesis, and deposition of new cell wall material. To better understand
the organization of the fungal cell we are pursuing three related projects.
(1) Polarity and the swo mutants. When Aspergillus nidulans spores break
dormancy and begin to grow, they undergo nuclear division along with
regular, predictable morphological changes. These morphological changes
serve as landmarks for ordering events in early growth. We have documented
the nuclear state and associated morphological landmarks in early growth
for A. nidulans and A. fumigatus (Momany and Taylor, 2000). This study
furnishes a framework for polarity and cell cycle investigations in our
lab.
We have identified and characterized temperature-sensitive swollen (swo)
mutants that have defects in the switch from isotopic to polar growth, an
important early landmark (Momany et al., 1999). Analysis of these mutants
showed that polarity establishment in A. nidulans is a two-step process and
that continued polar growth requires a persistent signal.
Recently, we have cloned five swo genes (swoA, C, D, F, and H) by
complementation (Shaw, Lin, and Momany). Using a transposon tagging system,
four of the genes have been sequenced and regions of the gene required for
function have been defined. We are further characterizing these gene
products.
(2) The septins are a group of proteins that localize to the neck in the
budding yeast Saccharomyces cerevisiae. The septins act as a scaffold,
recruiting and tethering other proteins to the division site. More than
twenty proteins that rely on septins to get to the division site have been
identified in yeast. Among the proteins that septins recruit are cell cycle
regulators. This raises the possibility that the septins not only organize
the structure of the division site, but also coordinate nuclear division
with cytokinesis. Using PCR and genome project searches we have identified
five septin homologues in A. nidulans (Momany et al., 2001).
One of these septins, AspB, localizes to septa, branches, and reproductive
structures. The localization of AspB at these different sites appears to be
under different cell cycle control. We are investigating localization,
interactions, and functions of this important group of scaffold proteins.
(2) Antibodies against the Aspergillus fumigatus cell wall. A. fumigatus
is a pathogen of the immunocompromised and is closely related to the model
filamentous fungus A. nidulans. We have isolated monoclonal antibodies
against A. fumigatus cell walls. These antibodies show several interesting
localization patterns. One of these antibodies recognizes a protein epitope
that appears to be exposed during polarity establishment and growth. We are
using this antibody collection to probe changes in the cell wall during
early fungal development.
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