bims-ciryme 2024-03-03 papers

Issue of 2024‒03‒03
two papers selected by
Gabriela Da Silva Xavier, University of Birmingham

Nat Commun. 2024 Feb 27. 15(1): 1788

The emergence of circadian timekeeping in the intestine.

Kathyani Parasram, Amy Zuccato, Minjeong Shin, Reegan Willms, Brian DeVeale, Edan Foley, Phillip Karpowicz.

The circadian clock is a molecular timekeeper, present from cyanobacteria to mammals, that coordinates internal physiology with the external environment. The clock has a 24-h period however development proceeds with its own timing, raising the question of how these interact. Using the intestine of Drosophila melanogaster as a model for organ development, we track how and when the circadian clock emerges in specific cell types. We find that the circadian clock begins abruptly in the adult intestine and gradually synchronizes to the environment after intestinal development is complete. This delayed start occurs because individual cells at earlier stages lack the complete circadian clock gene network. As the intestine develops, the circadian clock is first consolidated in intestinal stem cells with changes in Ecdysone and Hnf4 signalling influencing the transcriptional activity of Clk/cyc to drive the expression of tim, Pdp1, and vri. In the mature intestine, stem cell lineage commitment transiently disrupts clock activity in differentiating progeny, mirroring early developmental clock-less transitions. Our data show that clock function and differentiation are incompatible and provide a paradigm for studying circadian clocks in development and stem cell lineages.

DOI: https://doi.org/10.1038/s41467-024-45942-4

Commun Biol. 2024 Feb 28. 7(1): 243

Ror homolog nhr-23 is essential for both developmental clock and circadian clock in C. elegans.

Shingo Hiroki, Hikari Yoshitane.

Animals have internal clocks that generate biological rhythms. In mammals, clock genes such as Period form the circadian clock to generate approximately 24-h biological rhythms. In C. elegans, the clock gene homologs constitute the "developmental clock", which has an 8-h period during larval development to determine the timing of molting. Thus, the ancestral circadian clock has been believed to evolve into the oscillator with a shorter period in C. elegans. However, circadian rhythms have also been observed in adult C. elegans, albeit relatively weak. This prompts the question: if the clock gene homologs drive the developmental rhythm with 8-h period, which genes generate the circadian rhythms in C. elegans? In this study, we discovered that nhr-23, a homolog of the mammalian circadian clock gene Ror, is essential for circadian transcriptional rhythms in adult C. elegans. Interestingly, nhr-23 was also known to be essential for the molting clock. The bilaterian ancestral circadian clock genes might have evolved to function over multiple periods depending on developmental contexts rather than a single 8-h period in C. elegans.

DOI: https://doi.org/10.1038/s42003-024-05894-3