| Summary: | <p>This thesis describes a program of investigation carried out by the author at MRC Harwell that
shows, for the first time, that the gene Zfhx3 plays a role in modulating the circadian clock.
The work has used the short circuit (Sci) mouse model to assess the molecular and genetic role
of Zfhx3 in circadian behaviour and visual processing.</p>
<p>The Sci mutant was identified in an ENU mutagenesis dominant screen at MRC Harwell. The
causative mutation was found in a highly conserved region of zinc finger homeobox 3 (Zfhx3),
previously not known to play a role in the function of the circadian clock.</p>
<p>This study has shown that Zfhx3 RNA is specifically expressed in the adult SCN. Additionally,
co-immunoprecipitation has shown that ZFHX3 can interact with core clock proteins, CRY1,
CRY2 and PER2 and the Sci mutation causes differential effects on the RNA expression of Cry1,
Cry2 and Per1. Genetic interaction experiments identified an interaction between Sci and Cry2
under constant darkness and a potential interaction between Sci and Cry1 and Cry2 under
constant light. Together, these data indicate that Zfhx3 has a role in modulating the core
circadian oscillator, in particular through cryptochromes.</p>
<p>A role for Zfhx3 has also been identified in visual processing and retinal function. Zfhx3 RNA
was shown to be highly expressed in the ganglion, inner and outer nuclear layers of the retina.
Sci mutants have increased retinal sensitivity by 20 fold, which may be attributed to a
decrease in GABA neurotransmission in the retina.</p>
<p>From this study, novel functions for Zfhx3 within the circadian and visual systems have been
identified. This exemplifies that molecular components of the circadian oscillator may remain
to be identified and forward genetic approaches are facilitating advancements in this field.</p>
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