Seasonal expression patterns of clock-associated genes in the blue mussel Mytilus edulis

ABSTRACT

Environmental cues allow organisms to synchronise their internal biological rhythms with external environmental cycles. These rhythms are regulated on a molecular level by oscillating interactions between clock genes and their proteins. Light is a particularly relevant environmental cue, provisioning daily information via light/dark cycles as well as seasonal information via day-length (photoperiod). Despite the ecological and commercial importance of bivalves, little is known about the interactions comprising their molecular clock mechanism. This study investigates the link between the annual seasonal progression and reproductive development in the blue mussel (Mytilus edulis), using mRNA expression patterns of clock-associated genes: Clock, Cry1¸ ARNT, Timeout-like, ROR/HR3 and aaNAT, in the gonads of both sexes, sampled over three daily time-points on a tidal beach during the winter and summer solstices. Significant differences in mRNA expression levels, including some seasonal differences at comparable time-points, were detected for all genes with the exception of Timeout-like. These differences occurred seasonally within sex (Clock, Cry1, ROR/HR3), seasonally between sexes (Clock, Cry1, ARNT, ROR/HR3, aaNAT) and daily between sexes (Cry1), although no significant daily differences were detected in summer or winter for either sex for any of the genes. This study reveals that clock-associated genes show seasonal responses in this species of bivalve. Understanding the mechanisms by which environmental cues drive biological rhythms is critical to understanding the seasonal sensitivity of this keystone species to environmental changes.

Keywords:

• Circadian
• clock
• cryptochrome
• gametogenesis
• mRNA expression
• Mytilus
• photoperiod
• reproduction
• season

Acknowledgements

The authors wish to acknowledge David O’Neill and Dr Rose Wilcox for assistance with sample collection and dissection, and Dr Andrew Gracey for the provision of M. californianus clock gene and primer sequences.

Declaration of interest statement

The authors have no conflicts of interest to declare. The content of this paper is the responsibility of the authors alone.

Supporting information

Further information regarding sampling times is given in an additional figure. Multiple-species amino acid alignments and phylogenetic trees are also provided. Primers used for gene isolation are supplied as additional tables.

Supporting Information Cover Sheet

Authors: Emma C. Chapman, Alasdair R. O’Dell, Noha M. Meligi, Daniel R. Parsons and Jeanette M. Rotchell.

Manuscript Title: Seasonal expression patterns of clock-associated genes in the blue mussel Mytilus edulis

Summary: 18 pages: 3 Tables and 4 Figures.

Supporting Information Additional References

Hirayama J, Sassone-Corsi P. (2005). Structural and functional features of transcription factors controlling the circadian clock. Curr. Opin. Genet. Dev. 15:548-556.

Marchler-Bauer A, Lu S, Anderson JB, Chitsaz F, Derbyshire MK, DeWeese-Scott C, Fong JH, Geer LY, Geer RC, Gonzales NR, Gwadz M. (2011). CDD: a Conserved Domain Database for the functional annotation of proteins. Nucleic Acids Res. 39: D225-D229.

Supplemental material

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