The
Effects of Induced RevErb Circaidan
Oscillation
on Splicing of Tr? Gene
J Cotton
Xavier
University
Summer
Mentor: Dr. Stephen Munroe
Circadian
Rhythms are oscillations in a given event based on an approximate 24 hour
time period; such events include sleep wake cycles, body temperature, and
hormonal secretion. At the molecular level these events are based on clock
genes and proteins that interact, forming positive and negative feedback
loops. In mammalian cells the master clock is housed in the Suprachiasmic
Nucleus (SCN), a group of 10,000 neurons located in the hypothalamus. The
SCN synchronizes rhythms in peripheral cells via electric and hormonal
signals. Peripheral clocks have been show to cycle with a phase delay as
compared to the central oscillator.
Rev-Erb?,
plays an integral role in the cycling of core clock genes, meaning that
its oscillation is essential for central clock functions. In the realm
of antisense mechanisms, there is an overlap between the 3’ UTR of Rev-Erb?
and exon 10 of TR? gene. TR? is alternatively spliced yielding TR? 1 and
TR? 2. The overlap of TR? and Rev-Erb? is known as a natural cis-antisense
transcript. Rev-Erb? mRNA seems to inhibit splicing of TR? 2, whose protein
lacks a c terminus therefore compromising its ability to bind T3 (thyroid
hormone). However, it does bind DNA and inhibits the transcription of the
given gene, usually those responsible for growth factors. TR? 1 is capable
of binding T3 and subsequently activating gene expression. We have induced
circadian expression by shocking rat -1 fibroblast and C6 cells with excess
horse serum. The induction of cycling provides a system from which we can
determine if Rev-Erb?, regulates circadian activity of thyroid hormone
through antisense regulation of the overlapping TR? 2 gene as well through
its well characterized function as a transcriptional repressor.
In
our studies we noted cycling of Rev-Erb? in C6 cells. TR? transcript levels
must be determined. However, TR? 2 mRNA is rather stable due to an extended
half life, while the half life of Rev-Erb? is 15 min. Thus we hypothesize
that amplitude of TR? 2 oscillations may not vary dramatically, however
we expect to observe some induction of cycling with varying Rev-Erb? levels.
Further investigation must be undertaken in order to understand the physiological
effects of our investigated system. Ideally, we expect thyroid hormone
response to dampened with higher levels of TR? expression, and response
may increase with a higher TR? 1/ TR? 2 ratio. |
