The ubiquity of circadian systems has allowed their characterization in a broad range of
model systems, which has greatly improved knowledge of how these systems are
organized and the vast range of cellular and organismal processes under circadian
control. Most of the advances, however, have come in describing the central oscillators
of these systems, and, in some cases, the input pathways used to coordinate these
oscillators to external time. Very little progress has been made in understanding the
output pathways that allow circadian systems to regulate the breadth of processes shown
to be clock-controlled.
A genetic selection was designed to obtain mutations in genes involved in circadianregulated
expression of the Neurospora crassa ccg-1 and ccg-2 genes. Some, but not all,
of the strains obtained display altered regulation of more than one ccg as well as an ‘Easlike’
appearance on solid media, and altered circadian period on race tubes. The data
suggest a model in which output from the clock to these two genes is through a single,
bifurcated pathway. The cloning of the gene mutated (rrg-1) in one of the strains from the above selection
led to the first molecular description of a circadian output pathway in Neurospora, the
HOG MAP kinase pathway. The HOG pathway has been previously described with
regard to its role in the osmotic-stress response. The discovery of the involvement of
rrg-1 in circadian regulation of ccg-1 and ccg-2 led to the discovery of regulation of the
HOG pathway by the circadian clock. The data indicate that osmotic stress information
and time-of-day information are transduced through the HOG pathway and implicate a
role for the clock in preparing the organism for daily occurrences of hyperosmotic stress
associated with sun exposure.
The genetic selection, and the description of the HOG pathway with regard to circadian
output, provide a basis for further characterization of circadian output in Neurospora.
The ubiquity of MAP kinase pathways, such as the HOG pathway, and the observed
similarities in the mechanisms of circadian clock function across multiple phyla, indicate
that these findings may well be applicable to other model systems.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-1338 |
| Date | 15 May 2009 |
| Creators | Vitalini, Michael William |
| Contributors | Bell-Pedersen, Deborah |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Dissertation, text |
| Format | electronic, application/pdf, born digital |
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