Circadian oscillations in protein and mRNA levels of the period gene of Drosophila melanogaster.

Content Provider	Semantic Scholar
Author	Zwiebel, Laurence J. Hardin, Paul E. Hall, Jeffrey C. Rosbash, Michael
Copyright Year	1991
Abstract	Introduction The penod gene (per) was identified in a screen for Drosophila mehnogastet. mutants that influenced circadian rhythms [ 11. Three mutations were identified an arrhythmic allele, pero1; a long-period (about 29 h) allele, perL; and a short-period (about 19 h) allele, p d . Although this gene's effects are wider than originally suspected [2], this pioneering study of Konopka & Benzer [ l ] established this field of circadian rhythm genetics and it has been followed in the ensuing 20 years by numerous studies, in a less numerous set of organisms, designed to identify and characterize genes and gene products that affect (influence, cause, underlie, etc.) or are affected by circadian rhythms [3-51. Studies on the per gene, on other Drosophila genes involved in rhythms, on Dosophila rhythms as studied from other perspectives, and on the genetics and molecular genetics of circadian rhythms in other species, have been reviewed frequently in recent years [3-71. Rather than re-review this literature, we will focus on some of the recent observations concerning circadian oscillations of the per protein and the per RNA made here at Brandeis [8-111, as well as present some previously unpublished experiments that extend these observations. Circadian rhythms are scrutinized, almost defined, by three criteria. First, they persist under constant conditions (i.e. they 'free-run'), usually after a period of entrainment that consists of exposure to a cycling environmental stimulus within a 24 h period Secondly, they are sensitive to stimuli that indicate that the rhythms are not in synchrony with the cycling of the environment. For example, a pulse of light during the night will 'phase shift' the rhythms so that they are more in phase with the environmental cycles. For manay animals, their natural circadian periods are not exactly 24 h (circadian, from circa dies about a day) and so are phase shifted each day by the amval of daylight near the end of the animal's subjective night. Thirdly, circadian rhythms are usually temperature compensated so that the period is nearly independent of the temperature. While this makes intuitive sense (the day is still 24 h in cold weather or warm), it is at present just another fact that the biochemistry must ultimately explain. Drosophila locomotor activity rhythms conform well to all of these criteria as: (i) they free run under constant conditions; (ii) they can be phase shifted during subjective night and (iii) they show good temperature compensation [ 12-14]. They also can be viewed from the common perspective that circadian rhythms are generated by an interplay between three separate components: an input pathway (that is the route by which the clock communicates with the external environment), a clock or central oscillator, and an output pathway ('the hands of the clock'). In many ways, our attempts to interpret the recent observations concerning circadian fluctuations of per protein levels and per RNA levels are designed to understand how these fluctuations might fit with a role for the per gene product as part of one or more of these three components. They are also designed to shed light on where and how these three components might function and communicate with each other in Drosophih. The per gene was cloned and sequenced, and the genomic sequence compared with that of a number of cDNA clones [15-181. Although some splicing heterogeneity was discovered [ 181, the significance of these minor variants is still unclear. DNA fragments that contained the putative gene were used in transformation experiments to rescue the arrhythmic phenotype of pero' flies or of flies that are deficient for the DNA that encodes the per gene (perflies) [ 18-21]. Arguably, the most compelling evidence that links the 1218 amino acid open-reading frame, present within the rescuing fragment, with the per gene is the fact that each of the three original mutations can be accounted for by a single nucleotide substitution in this open-reading frame. The per'" mutation creates a stop codon at amino acid 464, a gratifying result given the virtually arrhythmic phenotype of the strain. PerS and perL are both due to missense mutations at amino acid 589 and amino acid 243, respectively [22,23]. Despite the strong evidence that the gene is defined molecularly, the sequence analysis was disappointing in that a relative with a defined biochemical function was not uncovered. There was some indication that the per gene product might be related to proteoglycans [17, 24, 251, but this sug-
File Format	PDF HTM / HTML
DOI	10.1042/bst0190533
PubMed reference number	1909668
Journal	Medline
Volume Number	19
Issue Number	2
Alternate Webpage(s)	http://www.biochemsoctrans.org/content/ppbiost/19/2/533.full.pdf
Alternate Webpage(s)	https://doi.org/10.1042/bst0190533
Journal	Biochemical Society transactions
Language	English
Access Restriction	Open
Content Type	Text
Resource Type	Article