The latest issue of The FEBS Journal, Issue 21, features an exciting collection of review articles focused on two themes, the first being muscle biology and the second circadian rhythm.

We invite you to read through the Editorial included in the issue [1], where The FEBS Journal Editorial Board Member Daniel Michele gives a comprehensive overview of the content of our recent Subject Collection on Muscle Biology and Disease. Our Subject Collections focus on previously published review and research content on a particular topic, and we encourage you to check this previously published content on muscle biology here.

Continuing on the review content of our latest Issue (Issue 21) , the State-of-the-Art review by Jie Chen and colleagues [2] summarises current knowledge on muscle cell-derived cytokines that function in an autocrine manner to regulate skeletal muscle differentiation and regeneration. In their State-of-the-Art review, Giulio Giuliani, Marco Rosina and Alessio Reggio overview the pathways and metabolic routes that can be targeted in order to halt and redirect the fibro/adipogenic potential of fibro/adipogenic progenitor cells (FAPs), while favouring their supportive role in muscle regeneration. The authors also discuss how single-cell technologies have facilitated the resolution of FAP transitional states with distinctive roles in muscle regeneration and disease [3]. In their Viewpoint article, Hamood AlSudais and Nadine Wiper-Bergeron describe a role for C/EBPβ in muscle stem cells and propose a functional intersection between C/EBPβ and NF-kB activity in the regulation of cancer cachexia [4]. In the second Viewpoint of the issue that focuses on muscle biology, Ori Avinoam and colleagues propose that cytosolic calcium-mediated coordination of myogenic differentiation, fusion and contraction is a feature selected in the amniotes to facilitate muscle regeneration [5].

In the State-of-the-Art review by Sarah Koop and Henrik Oster, the effect of the circadian clock system on behavioural outputs and its mediation through endocrine networks are described [6]. Yao Cai and Joanna Chiu review the role of Timeless (tim) in animal circadian clocks in their State-of-the-Art review featuring in this issue. Importantly, the authors provide a perspective on the identification of animal tim genes, overview the roles of TIM proteins in biological timing and genomic stability, and describe the similarities between dTIM with mTIM, despite their apparent functional divergence [7]. The State-of-the-Art review by Matthew Kayser and colleagues provides an overview of the development of circadian clocks, outputs, and behaviours across different species, with a particular focus on Drosophila [8]. In their State-of-the-Art review by Qingqing Lu and Jin Young Kim, the circadian networks mediated by the suprachiasmatic nucleus (SCN) are reviewed, and the authors’ perspective facilitates a better understanding of how the environment, brain, and peripheral tissues form networks for cooperation [9]. In their Viewpoint, Bharath Ananthasubramaniam and colleagues employ direct comparison of amplitudes and phases using artificial experiments on biological data to support their hypothesis that Venn diagram analysis overestimates the extent of circadian rhythm reprogramming [10]. Finally, Nuri Ozturk discusses how to study the light-dependent and magnetic field-dependent interactions of the hypothetical forms of Drosophila cryptochrome (DmCRY) in the complexomes in the last but not least Viewpoint featuring in the issue [11].

We hope that you find the review articles on the themes of muscle biology and circadian rhythm in this new issue timely and informative, and we invite you to read them in full here.

Note that Issue 21 includes also original articles that are not linked to the common themes of the review content (muscle biology and circadian rhythm).

Cover image: On the left: Myocytes, the type of cells found in muscle tissue. Smooth muscle consists of spindle shaped cells with single nucleus, 3d illustration, Shutterstock Illustration ID: 1583571424. On the right: The circadian rhythms are controlled by circadian clocks or a biological clock, which tell our brain when to sleep, tell our gut when to digest and control our activity during the day (right), Shutterstock Vector ID: 1391967521.

References:

1. Michele DE (2022) Mechanisms of skeletal muscle repair and regeneration in health and disease. FEBS J. Aug 5. doi: 10.1111/febs.16577.
2. Waldemer-Streyer RJ, Kim D & Chen J (2022) Muscle cell-derived cytokines in skeletal muscle regeneration. FEBS J. Jan 24;10.1111/febs.16372. doi: 10.1111/febs.16372.
3. Giuliani G, Rosina M & Reggio A (2021) Signaling pathways regulating the fate of fibro/adipogenic progenitors (FAPs) in skeletal muscle regeneration and disease. FEBS J. Jun 18. doi: 10.1111/febs.16080.
4. AlSudais H & Wiper-Bergeron N (2021) From quiescence to repair: C/EBPβ as a regulator of muscle stem cell function in health and disease. FEBS J. Dec 1. doi: 10.1111/febs.16307.
5. Sinha S, Elbaz-Alon Y &Avinoam O (2022) Ca²⁺ as a coordinator of skeletal muscle differentiation, fusion and contraction. FEBS J. Jun 11. doi: 10.1111/febs.16552.
6. Koop S & Oster H (2021) Eat, sleep, repeat - endocrine regulation of behavioural circadian rhythms. FEBS J. Jul 6. doi: 10.1111/febs.16109.
7. Cai YD & Chiu JC (2021) Timeless in animal circadian clocks and beyond. FEBS J. Oct 26;10.1111/febs.16253. doi: 10.1111/febs.16253.
8. Poe AR, Mace KD & Kayser MS (2021) Getting into rhythm: developmental emergence of circadian clocks and behaviors. FEBS J. Aug 10. doi: 10.1111/febs.16157.
9. Lu Q & Kim JY (2021) Mammalian circadian networks mediated by the suprachiasmatic nucleus. FEBS J. Oct 16. doi: 10.1111/febs.16233.
10. Pelikan A, Herzel H, Kramer A & Ananthasubramaniam B (2021) Venn diagram analysis overestimates the extent of circadian rhythm reprogramming. FEBS J. Jun 30. doi: 10.1111/febs.16095.
11. Ozturk N (2021) Light-dependent reactions of animal circadian photoreceptor cryptochrome. FEBS J. Nov 9. doi: 10.1111/febs.16273.