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Fidel Serrano

@fidelserrano.bsky.social
41 followers 74 following 12 posts

Postdoc Brunner Group | PhD University of Heidelberg | Circadian clocks and molecular timekeeping | First-generation immigrant scientist

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Fidel Serrano @fidelserrano.bsky.social · 15/06/2026
9/9 Finally, we saw that only the nuclear pool of CK1d could affect circadian period (with the cytoplasmic pool having no effect) further suggesting that this phosphorylation-mediated disruption of PER2-CRY1 interaction may serve as a transition mechanism from the early to the late repressive phase.
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Fidel Serrano @fidelserrano.bsky.social · 15/06/2026
8/9 Interestingly, these cytoplasmic PER2:CRY1:CK1d complexes could serve to buffer nuclear CRY1 protein concentrations, an important mechanism to consider when the clock needs to sustain sufficient CRY1 expression in the late repressive phase long after CRY1 mRNA expression has been repressed.
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Fidel Serrano @fidelserrano.bsky.social · 15/06/2026
7/9 Assembling the full PER2:CRY1:CK1d complex by overexpression, these complexes were cytoplasmic and contained less CRY1. This suggested that CK1d-driven PER2 phosphorylation may disrupt PER2-CRY1 interaction, potentially a novel mechanism to transition from the early to the late repressive phase.
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Fidel Serrano @fidelserrano.bsky.social · 15/06/2026
6/9 Overall, PER2 serves its known role as the stabilizing scaffold for the repressive complex bringing together CRY1 and CK1d; CRY1 determines the nuclear (and therefore effective) concentration of the complex; and CK1d seems to be a late entrant into the full circadian repressive complex.
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Fidel Serrano @fidelserrano.bsky.social · 15/06/2026
4/9 Knowing that the full repressive complex contains PER2, CRY1, and CK1d, we then asked when is CK1delta assembled into this complex? This line of inquiry also gave an interesting result: when CK1d is overexpressed, it showed that it was regulated dependent on kinase activity.
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Fidel Serrano @fidelserrano.bsky.social · 15/06/2026
3/9 This project began with the initial observation that when we overexpressed fluorescently-tagged PER2 and CRY1 in our U2OStx cells, they formed these interesting dynamic foci in the nucleus. Interestingly, the subcellular localization of these foci was dependent on the relative PER:CRY ratio
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