Early development of circadian rhythmicity in the suprachiamatic nuclei and pineal gland of teleost, flounder (Paralichthys olivaeus), embryos

Abstract

Circadian rhythms enable organisms to coordinate multiple physiological processes and behaviors with the earth's rotation. In mammals, the suprachiasmatic nuclei (SCN), the sole master circadian pacemaker, has entrainment mechanisms that set the circadian rhythm to a 24-h cycle with photic signals from retina. In contrast, the zebrafish SCN is not a circadian pacemaker, instead the pineal gland (PG) houses the major circadian oscillator. The SCN of flounder larvae, unlike that of zebrafish, however, expresses per2 with a rhythmicity of daytime/ON and nighttime/OFF. Here, we examined whether the rhythm of per2 expression in the flounder SCN represents the molecular clock. We also examined early development of the circadian rhythmicity in the SCN and PG. Our three major findings were as follows. First, rhythmic per2 expression in the SCN was maintained under 24 h dark (DD) conditions, indicating that a molecular clock exists in the flounder SCN. Second, onset of circadian rhythmicity in the SCN preceded that in the PG. Third, both 24 h light (LL) and DD conditions deeply affected the development of circadian rhythmicity in the SCN and PG. This is the first report dealing with the early development of circadian rhythmicity in the SCN in fish.

Seeing the light to change colour: An evolutionary perspective on the role of melanopsin in neuroendocrine circuits regulating light‐mediated skin pigmentation

“…In mammals and teleosts, pineal gland per1 and per2 increase at night to stimulate melatonin synthesis, which in LEI organisms causes melanosome aggregation. In contrast, melanophore per1 and per2 expression increases in the photophase, when melanosome dispersion occurs (Huang, Ruoff, & Fjelldal, ; Mogi, Uji, Yokoi, & Suzuki, ; Mogi, Yokoi, & Suzuki, ). This difference is explained by the fact that in mammals, melatonin production is not turned on directly by light, but rather as a result of SCN stimulation of phasic norepinephrine release from the dense sympathetic afferent nerve terminals that innervate the pineal gland (Figure ; Cagampang, Okamura, & Inouye, ; Coomans et al., ; Klein, ; Perreau‐Lenz et al., ; Simonneaux & Ribelayga, ).…”

Differential Impacts of the Head on Platynereis dumerilii Peripheral Circadian Rhythms

“…Molecular data on rhythms and clocks in marine invertebrates have become increasingly available over the last decade, now including the bivalves Mytilus californianus (Connor and Gracey, 2011) and Crassostrea gigas (Perrigault and Tran, 2017), the sea slugs Hermissenda crassicornis , Melibe leonina , and Tritonia diomedea (Cook et al, 2018; Duback et al, 2018), the isopod Eurydice pulchra (Wilcockson et al, 2011; Zhang et al, 2013; O’Neill et al, 2015), the amphipod Talitrus saltator (Hoelters et al, 2016), the lobsters Nephrops norvegicus (Sbragaglia et al, 2015) and Homarus americanus (Christie et al, 2018), the mangrove cricket Apteronemobius asahinai (Takekata et al, 2012), the copepods Calanus finmarchicus (Häfker et al, 2017), and Tigriopus californicus (Nesbit and Christie, 2014), the Antarctic krill Euphausia superba (Mazzotta et al, 2010; Teschke et al, 2011; Pittà et al, 2013; Biscontin et al, 2017), the Northern krill Meganyctiphanes norvegica (Christie et al, 2018), the marine midge C. marinus (Kaiser and Heckel, 2012; Kaiser et al, 2016), and the marine polychaete P. dumerilii (Zantke et al, 2013; Schenk et al, 2019). On the marine vertebrate side, especially teleost fish species have been investigated (Park et al, 2007; Sánchez et al, 2010; Hur et al, 2011; Watanabe et al, 2012; Vera et al, 2013; Rhee et al, 2014; Toda et al, 2014; Mogi et al, 2015; Okano et al, 2017).…”

Cross‐species single‐cell landscape of vertebrate pineal gland

“…This gland has undergone profound evolutionary changes, demonstrating functional diversity and species‐specific adaptations in different classes of vertebrates. In lampreys, fish, and amphibians, the pineal gland possesses photoreceptors capable of generating melatonin rhythms through oscillator, photodetector, and melatonin‐synthesizing apparatus 3,4 . In birds and reptiles, the pineal photoreceptive cells, often referred to as modified photoreceptors, exhibit regressed outer segments with varying degrees of degenerated lamellar structures 5 .…”

“…In lampreys, fish, and amphibians, the pineal gland possesses photoreceptors capable of generating melatonin rhythms through oscillator, photodetector, and melatonin-synthesizing apparatus. 3,4 In birds and reptiles, the pineal photoreceptive cells, often referred to as modified photoreceptors, exhibit regressed outer segments with varying degrees of degenerated lamellar structures. 5 Conversely, the mammalian pineal gland functions as a neuroendocrine organ that receives optical stimuli via the retina-suprachiasmatic nucleus (SCN)superior cervical ganglion (SCG)-nervi conarii adrenergic pathway.…”