Differential regulation of Period 2 and Period 3 expression during development of the zebrafish circadian clock

Zebrafish Per2 maternal mRNA is present in early embryos, similar to Per3.

• Per2 rhythmic expression occurs later during embryonic development compared to Per3.
• Per2 is not necessary for maintaining rhythmic physiological outputs, such as melatonin synthesis, during embryogenesis.
• Per2 shows constant expression in the developing olfactory bulb and pituitary, unlike Per3.
• The distinct expression patterns of Per2 and Per3 may indicate specialized functions in forming the embryonic circadian system.

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