No Circadian Rhythms in Testis: Period1 Expression Is Clock Independent and Developmentally Regulated in the Mouse

Per1 gene expression in the testis is constant over a 24-hour period, with levels higher than peak values observed in other tissues.

• The expression of Bmal1 in the testis also remains constant, unlike its oscillating pattern in other tissues.
• Levels and phosphorylation state of the PER1 protein do not fluctuate throughout the day.
• Per1 is predominantly expressed in step 7 to 10 spermatids, indicating developmental regulation.
• The Clock transcript is mainly found in spermatogonia and spermatocytes until the first meiotic division.
• Per1 expression remains unchanged in testes from Clock mutant mice, suggesting CLOCK does not activate Per1 in male germ cells.
• The findings imply that the testis lacks a functioning circadian clock, contrasting with other peripheral tissues.

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