Aim: To elucidate the spatiotemporal relationships among D-serine, serine racemase, and D-amino acid oxidase (EC 1.4.3.3; DAO) in mouse cortex, striatum, cerebellum, heart, lung, liver, spleen, kidney, and skeletal muscle during mouse postnatal development.
Methods: The transcription levels of serine racemase and DAO were assayed by reverse transcription-polymerase chain reaction (RT-PCR). The protein levels of serine racemase were examined by Western blot. DAO activities were assayed by colorimetric method. D-serine was measured by HPLC.
Results: In cortex, striatum, and cerebellum, free D-serine increased drastically after birth and coincided well with the increase of serine racemase expression. However, among the 9 tissues examined, DAO activities were detected only in cerebellum and kidney. During the 3rd week, DAO activity in cerebellum and kidney increased dramatically, which concurred with the drastic decline of D-serine content in these tissues. On the other hand, while D-serine and serine racemase fall to trace level in cerebellum and kidney at the 3rd weekend, DAO activities in these tissues increased continuously.
Conclusion: The free D-serine is mainly synthesized by serine racemase. However, novel mechanisms might be involved in D-serine deposition in mouse tissues with high level of D-serine and no detectable DAO activity such as cortex and striatum. DAO in cerebellum and kidney might have other physiological functions in addition to degrading D-amino acid.