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Hajime Tei(程 肇, テイ ハジメ born March 1959) is a Japanese neuroscientist specializing in the study of chronobiology. He currently serves as a professor at the Kanazawa University Graduate School of Natural Science & Technology. He is most notable for his contributions to the discovery of the mammalian period genes, which he discovered alongside Yoshiyuki Sakaki and Hitoshi Okamura.

Career
Between 1991 and 1992, Tei was a fellow for the Fellowships of the Japan Society for Japanese Junior Scientists at the University of Tokyo’s Institute of Medical Science. In 1992, Tei became an assistant professor at University of Tokyo’s Institute of Medical Science, a position he held until 2001, when he was promoted to associate professor. During his time as an assistant professor, Tei worked alongside Yoshiyuki Sakaki and Hitoshi Okamura to discover the mammalian period genes Per1, Per2, and Per3. They also discovered the mammalian homolog of the Drosophila gene timeless. He served as an associate professor until 2004. In 2004, Tei became the principal investigator of the Laboratory of Chronogenomics at Mitsubishi Kagaku Institute of Life Sciences. In 2009, he became a full professor at the Kanazawa University Graduate School of Natural Science & Technology, a position he currently serves to-date.

Discovery of Mammalian Period Genes
In 1997, Hajime Tei, Yoshiyuki Sakaki, and Hitoshi Okamura identified the human and mouse Per homologues of the Drosophila Per gene. They discovered that hPer (the human homolog of dPer) and mPer (the mouse homolog of dPer) encoded PAS-domain-containing polypeptides that are highly homologous to dPer. They also found that mPer showed autonomous circadian oscillation in its expression in the suprachiasmatic nucleus (SCN) which acts as the primary circadian pacemaker in the mammalian brain. They were able to discover this by using a method called intra-module scanning-polymerase chain reaction (IMS-PCR), which allowed them to screen out short stretches of DNA sequences and isolate mammalian homologs of the Drosophila Per gene. This achievement led to the differentiation of Per1, Per2, and Per3.

Identification of mammalian timeless homolog
In 1998, Hajime Tei, in collaboration with other researchers, identified a mammalian homolog of the Drosophila timeless gene. During this research project, timeless was mapped and sequenced in both humans and mice; it was found that the amino acid sequences between humans and mice were 83% identical. They discovered that the transcript was widely expressed in many of the tissues analyzed during the study using a technique called Northern blot analysis.

Discovery of circadian clocks in peripheral organs
Tei and Shin Yamazaki developed the first rodent model that monitored circadian gene expression rhythms using luminescence, and in 2000, they discovered the existence of circadian clocks in peripheral organs of mammals. This discovery led to the current understanding of mammalian circadian control as a multi-oscillatory system. He was also part of a team that discovered feeding cycles can entrain liver independently of the suprachiasmatic nucleus (SCN) and the light cycle. This raised the possibility that peripheral organs contain circadian clocks that are coupled to the SCN through rhythmic behaviors.

Regulation of bone resorption by circadian clocks
In 2016, a research team that included Tei discovered that clock genes, most specifically Bmal1 and Per1, are rhythmically expressed in osteoblasts to modulate the osteoblast-dependent regulation of osteoclastogenesis by regulating 1,25(OH)2D3-induced Rankl expression in osteoblasts. They were able to discover this through the use of cell cultures and real-time luciferase analysis, among many other methods.

Genetic Basis for Daytime Dead Zone
Most recently, in February 2019, Koichiro Uriu and Hajime Tei published their work on how daytime dead zones in circadian clocks are created. They hypothesized that daytime dead zones were a result of the saturation of biochemical reactions in negative feedback loops for circadian rhythms. In order to test this, they generated a dead zone with the degradation response seen in the Drosophila circadian clock. Then, they used a dimensionless three-variable Goodwin model to find the key determinants of the dead zones of a phase response curve (PRC). Through these methods they were able to determine that the saturation of a biochemical reaction in negative feedback loops was indeed the mechanism that created dead zones in PRC’s. They also found that this mechanism was a general design principle for dead zone generation found in most organisms.

Applications of Scientific Contributions
Tei holds a patent on a Per1 promoter sequence that, when operably linked to another gene, will rhythmically promote its transcription. This promoter sequence allows for the creation of transgenic animals that will be useful in studying circadian disorders and diseases. Additionally, pharmaceutical treatments for such diseases can be tested on transgenic animals with this specific promoter.

Collaborators
From early in his professional career to his work current projects, Tei has worked with many other chronobiologists. Specifically, he is listed as a recurring co-author with the following scientists :
 * Yoshiyuki Sakaki
 * Shin Yamazaki
 * Gene D. Block
 * Rika Numano
 * Michael Menaker

Media Attention
Tei’s work has been cited by many popular news media sources, such as HowStuffWorks, Quartz, The Seattle Times, and The New York Times. Despite this research recently coming to the public’s attention, no controversies or issues with Tei’s scientific achievements have been found.