Michael
E. Geusz
Department of Biological Sciences, BGSU
The physiology and behavior of
many organisms undergo daily changes with the help of internal biological
pacemakers that keep time while maintaining circadian rhythms in the
body. This circadian system synchronizes internal timing to external
24-hour cycles of light and dark while coordinating rhythmic processes in
multiple tissues. Circadian pacemakers have been identified in nearly all
organs of mammals, and the neural pacemaker in the suprachiasmatic
nucleus (SCN) of the hypothalamus appears to be a dominant node within these
timing networks. One current question is how the SCN and other circadian
pacemakers interact to remain in phase with each other and with the daily
cycles of the environment.
Research
areas
Neuronal
circadian clocks
By imaging luciferase
bioluminescence in brain slice cultures we were able to identify circadian
oscillations in mper1 gene expression
in the mesencephalic trigeminal nucleus of the
midbrain of mice (Hiler et al., 2008). We are determining how these cells compare with
the better understood circadian clock cells of the hypothalamic SCN. Because they are considerably larger than SCN
neurons they may provide advantages for imaging studies.
Cancer
biology
We used luciferase
bioluminescence imaging to detect mper1
gene expression in the stroma of LLC tumors of mice (Geusz et al, 2010). Current
projects are evaluating whether the circadian clock influences how tumor stromal cells support cancer cell growth.
Methods
for imaging gene expression in live mice
We have developed techniques for
imaging circadian rhythms in the clock cells of the SCN (Geusz, 2001;
Sigworth et al., 2003) and in the tissues of live mice (Collaco and Geusz,
2003 ; Collaco et al.,
2005, Hiler al, 2006). Several immediate-early genes are expressed
in the SCN. The immediate-early gene c-fos is an effective
marker for neural activity and is expressed in the SCN when animals are exposed
to light that shifts the phase of their circadian system. These phase
shifts serve to keep the circadian clocks synchronized with the daily cycles of
the environment. Using a transgenic mouse with the human c-fos
promoter controlling the firefly luciferase gene (fos::luc)
we are imaging c-fos
expression patterns in intact animals and brain slice cultures.
We are also imaging a second
transgenic mouse to identify where in the body cells are most permissive for
reactivating herpes virus infections and whether the circadian clock plays a
role. These mice contain the luciferase gene
controlled by the promoter and enhancer of the human cytomegalovirus major
immediate-early gene. This gene's induction
is required for reactivation of the virus from the latent state. The
transgenic mice were crossed with the hairless albino mouse strain HRS/J to
facilitate imaging of deep tissues (Collaco and Geusz,
2003). Because
the mice can be imaged repeatedly to follow ongoing or induced gene expression,
fewer animals are needed than with other methods to monitor cellular responses,
such as mRNA assays.
Multi-microelectrode recordings from neurons in culture
Many neurons can be recorded
simultaneously through gold microelectrodes embedded in the bottom of culture
dishes. This method is particularly well
suited for the long-term recordings needed for measuring circadian rhythms in
circadian clock neurons (Herzog et al, 1997
; Nunemaker et al., 2001).
Relevant Publications
Sigworth, L. A., Chandler,
T. R., Liao, L., and Geusz, M. E. (2001). Luciferase
imaging reveals distinct patterns of gene regulation in live brain
slices. In: Bioluminescence & Chemiluminescence : Proceedings of the 11th International Symposium on
Bioluminescence Chemiluminescence : Asilomar Conference Grounds, Pacific Grove, Monterey,
California, USA : 6-10 September 2000. J.F. Case et al . (eds.) World Scientific, New Jersey pp.
185-188.