Abstract
The PER3 gene is one of the clock genes, which function in the core mammalian molecular circadian system. A variable number of tandem repeats (VNTR) locus in the 18th exon of this gene has been strongly associated to circadian rhythm phenotypes and sleep organization in humans, but it has not been identified in other mammals except primates. To better understand the evolution and the placement of the PER3 VNTR in a phylogenetical context, the present study enlarges the investigation about the presence and the structure of this variable region in a large sample of primate species and other mammals. The analysis of the results has revealed that the PER3 VNTR occurs exclusively in simiiforme primates and that the number of copies of the primitive unit ranges from 2 to 11 across different primate species. Two transposable elements surrounding the 18th exon of PER3 were found in primates with published genome sequences, including the tarsiiforme Tarsius syrichta, which lacks the VNTR. These results suggest that this VNTR may have evolved in a common ancestor of the simiiforme branch and that the evolutionary copy number differentiation of this VNTR may be associated with primate simiiformes sleep and circadian phenotype patterns.
Highlights
The light/dark cycle that arises from the geospatial relationship between the Earth and the Sun has been shown to be the strongest environmental clue, or zeitgeber, for the entrainment of circadian rhythms in many organisms, including human beings [1,2]
The DNA analysis of the Period circadian clock 3 (PER3) variable number of tandem repeats (VNTR) region belonging to the New World primates revealed that all of the studied individuals carried this locus in their genomes, the number of repeats varied among the different species (Figure 1 and Figure S1)
The present study demonstrates that the VNTR in the PER3 gene is a genomic structure present in all Simiiforme primates studied, the number of repeats is different, depending on the species
Summary
The light/dark cycle that arises from the geospatial relationship between the Earth and the Sun has been shown to be the strongest environmental clue, or zeitgeber, for the entrainment of circadian rhythms in many organisms, including human beings [1,2]. All physiological processes, such as hormone secretion, sleep, and body temperature which oscillate with circadian periodicity, are regulated by the light/dark signal [3] The processing of this signal is associated with the expression of a group of genes, collectively known as clock genes, which are directly involved in the regulation and maintenance of the circadian rhythms [4,5]. Period circadian clock 3 (PER3) is one of the clock genes engaged in the core mammalian molecular circadian system [7,8] In humans, this gene is located on the short arm of chromosome 1 (1p36) [9], and its 18th exon contains a polymorphic variable number of tandem repeats (VNTR) composed of a 54-bp motif that is repeated either four or five times [10]. Several reports have shown associations between this VNTR and human circadian rhythm phenotypes, including morning/evening preferences, delayed sleep phase disorder (DSPD), and homeostatic regulation of sleep [10,12,13,14,15,16], highlighting an important link between genetics, the sleep/wake cycle and adaptation to the light/dark cycle
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