Identification of the Molecular Clockwork of the Oyster Crassostrea gigas

Abstract

Molecular clock system constitutes the origin of biological rhythms that allow organisms to anticipate cyclic environmental changes and adapt their behavior and physiology. Components of the molecular clock are largely conserved across a broad range of species but appreciable diversity in clock structure and function is also present especially in invertebrates. The present work aimed at identify and characterize molecular clockwork components in relationship with the monitoring of valve activity behavior in the oyster Crassostrea gigas. Results provided the characterization of most of canonical clock gene including clock, bmal/cycle, period, timeless, vertebrate-type cry, rev-erb, ror as well as other members of the cryptochrome/photolyase family (plant-like cry, 6–4 photolyase). Analyses of transcriptional variations of clock candidates in oysters exposed to light / dark regime and to constant darkness led to the generation of a putative and original clockwork model in C. gigas, intermediate of described systems in vertebrates and insects. This study is the first characterization of a mollusk clockwork. It constitutes essential bases to understand interactions of the different components of the molecular clock in C. gigas as well as the global mechanisms associated to the generation and the synchronization of biological rhythms in oysters.

Sequences of Circadian Clock Proteins in the Nudibranch Molluscs Hermissenda crassicornis, Melibe leonina, and Tritonia diomedea

“…4). This mirrors the situation in other lophotrochozoans investigated to date (Arendt et al, 2004; Zantke et al, 2013; Bao et al, 2017; Perrigault and Tran, 2017), as well as in crustaceans (Zhang et al, 2013) and some insects (Rubin et al, 2006). …”

“…Lophotrochozoans, such as molluscs, represent an animal clade that can potentially shed some light on this question. Recent research on the oyster Crassostrea gigas found that the bivalve circadian clock may be intermediate to that seen in mammals and Drosophila , with both TIMELESS and NPCRY possibly acting as transcriptional repressors and PCRY providing light input to the clock (Perrigault and Tran, 2017). This is actually similar to the proposed clock mechanism in some non-drosopholid insects, such as butterflies (Zhu et al, 2008), and the chelicerate Limulus (horseshoe crab) (Chesmore et al, 2016).…”

“…The nudibranch PERIOD proteins were most closely related to other molluscs but, unlike CLOCK and BMAL1, shared more recent common ancestry with arthropods than chordates, though with low bootstrap support for this relationship. The tree was rooted on NEURONAL NPAS DOMAIN PROTEIN (NPAS) from the oyster Crassostrea gigas (Perrigault and Tran, 2017). …”

“…As described above, these molecular clocks are quite similar operationally, but they differ in the proteins used for negative feedback and how light input is transmitted to the clock. While circadian genes have been identified in some species in the other major protostome lineage, Lophotrochozoa (Zantke et al, 2013; Bao et al, 2017; Perrigault and Tran, 2017; Schnytzer et al, 2018), we do not yet fully understand the molecular mechanisms underlying clocks in lophotrochozoans as a group. Further elucidating the molecular basis of circadian clocks in this clade may shed light on the evolution of circadian clocks.…”

Bivalve mollusc circadian clock genes can run at tidal frequency

“…Recently, the complete genome of this species was published [20]. Moreover, circadian clock genes and the cyclic transcriptome have been studied in C. gigas [21,22], making it an ideal candidate to investigate molecular clockwork and test hypotheses to explain circatidal rhythmicity.…”