
Body parts respond to day and night independently from brain - conse_lad
https://news.uci.edu/2019/05/30/uci-research-helps-shed-new-light-on-circadian-clocks/
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conse_lad
From the journals:

1\. Defining the Independence of the Liver Circadian Clock

Mammals rely on a network of circadian clocks to control daily systemic
metabolism and physiology. The central pacemaker in the suprachiasmatic
nucleus (SCN) is considered hierarchically dominant over peripheral clocks,
whose degree of independence, or tissue-level autonomy, has never been
ascertained in vivo. Using arrhythmic Bmal1-null mice, we generated animals
with reconstituted circadian expression of BMAL1 exclusively in the liver
(Liver-RE). High-throughput transcriptomics and metabolomics show that the
liver has independent circadian functions specific for metabolic processes
such as the NAD + salvage pathway and glycogen turnover. However, although
BMAL1 occupies chromatin at most genomic targets in Liver-RE mice, circadian
expression is restricted to ∼10% of normally rhythmic transcripts. Finally,
rhythmic clock gene expression is lost in Liver-RE mice under constant
darkness. Hence, full circadian function in the liver depends on signals
emanating from other clocks, and light contributes to tissue-autonomous clock
function.

[https://www.cell.com/cell/fulltext/S0092-8674(19)30444-1?_re...](https://www.cell.com/cell/fulltext/S0092-8674\(19\)30444-1?_returnURL=https%3A%2F%2Flinkinghub.elsevier.com%2Fretrieve%2Fpii%2FS0092867419304441%3Fshowall%3Dtrue)

2\. BMAL1-Driven Tissue Clocks Respond Independently to Light to Maintain
Homeostasis

Circadian rhythms control organismal physiology throughout the day. At the
cellular level, clock regulation is established by a self-sustained
Bmal1-dependent transcriptional oscillator network. However, it is still
unclear how different tissues achieve a synchronized rhythmic physiology. That
is, do they respond independently to environmental signals, or require
interactions with each other to do so? We show that unexpectedly, light
synchronizes the Bmal1-dependent circadian machinery in single tissues in the
absence of Bmal1 in all other tissues. Strikingly, light-driven tissue
autonomous clocks occur without rhythmic feeding behavior and are lost in
constant darkness. Importantly, tissue-autonomous Bmal1 partially sustains
homeostasis in otherwise arrhythmic and prematurely aging animals. Our results
therefore support a two-branched model for the daily synchronization of
tissues: an autonomous response branch, whereby light entrains circadian
clocks without any commitment of other Bmal1-dependent clocks, and a memory
branch using other Bmal1-dependent clocks to “remember” time in the absence of
external cues.

[https://www.cell.com/cell/fulltext/S0092-8674(19)30507-0?_re...](https://www.cell.com/cell/fulltext/S0092-8674\(19\)30507-0?_returnURL=https%3A%2F%2Flinkinghub.elsevier.com%2Fretrieve%2Fpii%2FS0092867419305070%3Fshowall%3Dtrue)

