Aspergillus nidulans
Role of PaxB in Septum Formation
One of the classic septation-deficient mutations in Aspergillus nidulans is the temperature-sensitive sepD5 mutation, whose gene locus,
despite the mutation's having been discovered as long
ago as 1975, had not (until now) been identified. Through Next-Generation whole-genome sequencing, we have demonstrated
that the sepD5 mutation lies in the A. nidulans orthologue encoding the paxillin-related protein PaxB. By tagging PaxB with
GFP or tdTomato fluorescent tags, we demonstrated that the protein localizes to the cell-apex structure known as the Spitzenkörper
and that it colocalizes with components of the contractile actomyosin ring during cytokinesis. By deleting the
gene encoding PaxB, we also show that PaxB is necessary for recruitment of several key proteins to the site of cell division.
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The top image depicts the domain structure of A. nidulans IQGAP, where G/R designates the predicted amino acid substitution.
E = Normal distribution of septal crosswalls; F = Absence of crosswalls after IQGAP gene deletion; G = Absence of crosswalls after gene down-regulation |
Among several other things demonstrated regarding A. nidulans IQGAP is evidence that it binds to the EF-hand protein Cdc4 (myosin essential light chain)
but not to EF hand proteins calmodulin (CamA) or myosin regulatory light chain (MrlC). IQGAP does not, however, require Cdc4 in order to localize
to sites of septation.
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C = IQGAP at septation site; D = Cdc4 at septation site; H = Localization of IQGAP in the
absence of Cdc4; I = The same cell stained to show failure to form septa in the absence of Cdc4 |
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Literature:
Hill, T. W, K. E. Wendt, D. A. Jones, M. H. Williamson, U. J. Ugwu, L. B. Rowland, and L. Jackson-Hayes.
The Aspergillus nidulans IQGAP orthologue SepG is required for constriction
of the contractile actomyosin ring. Fungal Genetics & Biology 144: 103439.