Clock gene and gene product

Details Clock gene and gene product Clock gene and gene product

2000-02-03

2001-09-18

Carlson, Karen Cochrane (Department: 1653)

Drug, bio-affecting and body treating compositions

Designated organic active ingredient containing

Peptide containing doai

C530S350000

Reexamination Certificate

active

06291429

ABSTRACT:

TECHNICAL FIELD OF THE INVENTION
The field of the present invention is the circadian clock of mammals. More particularly, the present invention relates to mammalian genes and gene products that regulate aspects of the circadian rhythm in mammals and those processes controlled by the circadian rhythm.
BACKGROUND OF THE INVENTION
Circadian rhythms are a fundamental property of all eukaryotic and some prokaryotic organisms (Takahashi 1995). The underlying molecular mechanism appears similar among living systems, is cell autonomous and involves periodic macromolecular synthesis. Alterations in circadian rhythms are involved in sleep disorders such as “delayed sleep phase syndrome” which may be an alteration in the circadian period (lengthening) and the entrainment system. There is also evidence for circadian rhythm abnormalities in affective disorders. The most consistent feature of circadian rhythms observed in depressed patients is that a variety of physiological events occur earlier than normal (usually referred to as a “phase advance”). A shortened REM latency after sleep onset, which can be the manifestation of a change in the circadian coupling or organization of rhythms, appears to be a prominent characteristic of depression.
Further, a number of diagnostic tests depend on the time of day at which the test is performed. These include the dexamethasone suppression test for depression, intraocular pressure measurements for glaucoma, and plasma cortisol concentration for Addison's disease and Cushing's syndrome. In addition, a number of clinical treatments (such as chemotherapy or alleviation of hypertension) can be optimized through the delivery of therapeutic agents at the appropriate time of day. Circadian rhythmicity appears to be deeply embedded in most aspects of the biology of organisms—indeed it is a central feature of their organization. It seems unlikely that complete understanding of most regulatory processes can be achieved without an appreciation of their circadian dimensions.
Clock genes have been described in other model systems, most notably in Drosophila and Neurospora. Three known clock genes have been characterized at the molecular and functional level. These are the period (per) and timeless (tim) genes in Drosophila, and the frequency (frq) gene in Neurospora. This work is known to the art and is described in review papers by J. S. Takahashi,
Annual Review of Neuroscience
18:531-553, 1995; and by J. C. Dunlap,
Annual Review of Genetics
30:579-601, 1996. None of these three clock genes have been shown to possess a protein motif known to allow these proteins to bind DNA, rather it appears that in the case of PERIOD and TIMELESS, these proteins must interact with unidentified DNA-binding transcription factors.
The genetic approach to circadian rhythms was first described by Ron Konopka and Seymour Benzer (1971) who isolated single-gene mutations that altered circadian periodicity in Drosophila. In a chemical mutagenesis screen of the X chromosome, they found three mutants that either shortened (per
S
), lengthened (per
L
) or abolished (per
0
) circadian rhythms of eclosion and adult locomotor activity. In 1984, two groups at Brandeis and Rockefeller independently cloned per in a series of experiments that showed that germline transformation with DNA could rescue a complex behavioral program (reviewed in Rosbash & Hall 1989). Each of the mutant per alleles is caused by intragenic point mutations that produce missense mutations in per
S
and per
L
, and a nonsense mutation in per
0
(Bayfies et al. 1987, Yu et al. 1987). Only recently has the nature of per gene product (PER) become more clear. The Drosophila single-minded protein (SIM) (Nambu et al. 1991), the human aryl hydrocarbon receptor nuclear translocator (ARNT) (Hoffirian et al. 1991), and the aryl hydrocarbon receptor (AHR) (Burbach et al. 1992) all share with PER a domain called PAS, (for PER, ARNT, SIM) (Nambu et al. 1991). The PAS domain contains about 270 amino acids of sequence similarity with two 51-amino acid direct repeats. Recent work shows that the PAS domain can function as a dimerization domain (Huang et al.1993). Because other PAS members are transcriptional regulators and PER can dimerize to them, PER could function as a transcriptional regulator either by working in concert with apartner that carries a DNA-binding domain, or by acting as a dominant-negative regulator by competing with a transcriptional regulator for dimenization or DNA binding. Consistent with this role, PER is predominantly a nuclear protein in the adult central nervous system of Drosophila (Liu et al. 1992).
The expression of PER itself is circadian, and both per mRNA and PER protein abundance levels oscillate. Hardin et al. (1990) showed that per mRNA levels undergo a striking circadian oscillation. The per RNA rhythm persists in constant darkness and the period of the RNA rhythm is ~24 hours in per
+
flies and is ~20 hours in per
S
flies. The RNA of per
0
flies is present at a level ~50% of normal flies, but does not oscillate. In per
0
flies that have been rescued by gernline transformation with wild-type per+DNA, both circadian behavior and per RNA cycles are restored. Importantly, in these transformed flies both the exogenousper
+
RNA and the endogenous per
0
RNA levels oscillate. In addition to a per RNA cycle, the PER protein also shows a circadian rhythm in abundance (Siwicki et al. 1988, Zerr et al. 1990, Edery et al. 1994b). The rhythm in PER protein also depends on per, because per
O
flies do not have a protein rhythm and because per mutants alter the PER rhythm (Zerr et al. 1990). Therefore, the circadian expression of per mRNA and protein levels both depend on an active per gene. Because per
S
shortens the period of the RNA cycle and because per
+
DNA transformation rescues per
0
RNA cycling, PER protein expression clearly regulates per RNA cycling. Hardin et al. (1990) propose that feedback of the per gene product regulates its own mRNA levels. Support for such a model has been provided by showing that transient induction of PER from a heat shock promoter/per cDNA transgene in a wild-type background can phase shift circadian activity rhythms in Drosophila (Edery et al. 1994a).
The PER protein rhythm appears to be regulated at both transcriptional and post-transcriptional levels. Hardin et al. (1992) have shown that levels of per precursor RNA cycle in concert with mature per transcripts. In addition, per promoter/CAT fusion gene constructs show that per 5′ flanking sequences are sufficient to drive heterologous RNA cycles. These results suggest that circadian fluctuations inper mRNA abundance are controlled at the transcriptional level. In addition to a rhythm in per transcription and PERabundance, PER appears to undergo multiple phosphorylation events as itaccumulates each cycle (Edery et al. 1994b). The nature and functional significance of the PER phosphorylation sites, however, are not known at this time. Interestingly, the peak of the per RNA cycle precedes the peak of the PER protein cycle by about 4-6 hours. The reasons for the lag in PER accumulation are not well understood. However, the recent isolation of a second clock mutant, named timeless (tim), has provided significant insight (Sehgal et al. 1994). Tim mutants fail to express circadian rhythms in eclosion and locomotor activity, but more importantly also fail to express circadian rhythms in per mRNA abundance (Sehgal et al. 1994). Furthermore, the nuclear localization of PER is blocked in tim mutants (Vosshall et al. 1994). In 1995, tim was cloned by positional cloning and by interaction with the PAS domain of PER in a yeast two-hybrid screen (Gekakis et al. 1995, Myers et al. 1995). Like PER, TIM is a large protein without any obvious sequence homologies to other proteins. While PER dimerizes to TIM via the PAS domain, TIM is not a member of the PAS family. The expression of tim RNA levels has a striking circadian oscillation which is in phase with the per RNA rhythm. The rhythm in tim RN

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