CHANGES IN PROTEIN-PHOSPHORYLATION IN THE EYE OF APLYSIA ASSOCIATED WITH CIRCADIAN-RHYTHM REGULATION BY SEROTONIN

Serotinin (5‐HT) shifts the phase of the circadian oscillator of the eye of Aplysia californica in a phase dependent manner. This indicates that 5‐HT acts, either directly or through some intermediaries, on a component of the oscillator. Since our goal is to identify the components of the oscillator, we are following the pathway through which 5‐HT has its effect on the rhythm. The effect of 5‐HT on the rhythm has been shown to be mediated by an increase in intracellular cyclic adenosine‐3′,5′‐monophosphate (cAMP). The most likely action of cAMP is to activate cAMP‐dependent protein kinase. Therefore, we used two‐dimensional polyacrylamide gel electrophoresis to investigate changes in 32P labelled phosphoproteins which occur with 5‐HT and other treatements. Fourteen proteins showed increased incorporation of 32P when eyes were exposed to treatments of 5‐HT from CT 06 to 12. Two proteins showed decreased incorporation. 8‐bt‐cAMP mimicked all but one of the increases and both decreases in incorporation produced by 5‐HT. 8‐bt‐cAMP increased incorporation into three additional proteins and decreased incorporation into three additional proteins and decreased incorporation into three other that were not affected by 5‐HT. Incorporation into one protein was increased by 5‐HT but decreased by 8‐bt‐cAMP. By comparison, light, which has little or no effect on the rhythm at this phase, only affected one protein. The protein increased by light was also increased by 5‐HT. Tetradecanoic phorbol acetate (TPA), administered during CT 06‐12, also had little effect on the rhythm at this phase. TPA increased incorporation into twenty proteins and decreased incorporatoin into three. Seven of the increased proteins were also increased by 5‐HT. Some of the phosphoproteins altered by 5‐HT and cAMP analogue may mediate the effect of 5‐HT on the circadian rhythm. Copyright © 1990 John Wiley & Sons, Inc.