Non-cyclic and Developmental Stage-Specific Expression of Circadian Clock Proteins During Murine Spermatogenesis1

Feb 28, 2003Biology of reproduction

Constant and stage-specific timing protein levels during mouse sperm development

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Abstract

Expression of circadian clock genes mPer1, mPer2, Bmal1, Clock, mCry1, and Npas2 in the mouse testis remains constant throughout the day.

Cyclic expression of circadian genes in peripheral tissues indicates they may have their own internal clocks.
The testis serves as a model for studying the influence of circadian rhythms on reproduction.
Immunohistochemical analysis shows mPER1 and CLOCK proteins are localized to specific developmental stages of spermatogenesis.
mPER1 is found in spermatogonia and condensing spermatids, while CLOCK is present only in round spermatids during acrosome development.
Findings suggest that clock proteins may have roles in spermatogenesis that are not related to circadian timing.
Similar noncircadian expression patterns of clock genes were observed in the thymus, indicating a potential link with cellular differentiation.

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The central circadian clock in mammals is housed in the brain and is based on cyclic transcription and translation of clock proteins. How the central clock regulates peripheral organ function is unclear. However, cyclic expression of circadian genes in peripheral tissues is well established, suggesting that these tissues have their own endogenous oscillators. Reproduction is a process influenced by circadian rhythms in many organisms, thus making the testis an attractive model for studying clock function in peripheral organs. However, results addressing cyclic expression of clock genes in the mammalian testis are inconsistent. To resolve this issue, RNA was extracted from testes of mice at various times of day. Expression of the circadian clock genes mPer1, mPer2, Bmal1, Clock, mCry1, and Npas2 was constant at all times. Immunohistochemical localization of mPER1 and CLOCK proteins revealed restricted expression only in cells at specific developmental stages of spermatogenesis. For mPER1, these stages are the spermatogonia and the condensing spermatids. In contrast, CLOCK expression was restricted to round spermatids, specifically within the developing acrosome. Expression of mPER1 and CLOCK was constant at all times of day. These results suggest that clock proteins have noncircadian functions in spermatogenesis. Noncircadian expression of clock genes was also found in the thymus, which, like the testis, is composed primarily of differentiating cells. We propose that cyclic expression of clock genes is suspended during cellular differentiation.

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Non-cyclic and Developmental Stage-Specific Expression of Circadian Clock Proteins During Murine Spermatogenesis1

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