The Circadian Clock Machinery During Early Development of Senegalese sole (Solea senegalensis): Effects of Constant Light and Dark Conditions

Abstract

Circadian rhythms are established very early during vertebrate development. In fish, environmental cues can influence the initiation and synchronization of different rhythmic processes. Previous studies in zebrafish and rainbow trout have shown that circadian oscillation of clock genes represents one of the earliest detectable rhythms in the developing embryo, suggesting their significance in regulating the coordination of developmental processes. In this study, we analyzed the daily expression of the core clock components Per1, Per2, Per3, and Clock during the first several days of Senegalese sole development (0–4 d post fertilization or dpf) under different lighting regimes, with the aim of addressing when the molecular clock first emerges in this species and how it is affected by different photoperiods. Rhythmic expression of the above genes was detected from 0 to 1 dpf, being markedly affected in the next few days by both constant light (LL) and dark (DD) conditions. A gradual entrainment of the clock machinery was observed only under light-dark (LD) cycles, and robust rhythms with increased amplitudes were established by 4 dpf for all clock genes currently studied. Our results show the existence of an embryonic molecular clock from the 1st d of development in Senegalese sole and emphasize the significance of cycling LD conditions when raising embryos and early larvae. (Author correspondence: [email protected]; [email protected])

Keywords:

• Circadian rhythm
• Clock genes
• Embryonic clock
• Fish
• Photoperiod

ACKNOWLEDGMENTS

We would like to thank Esther Isorna for her help during sampling, and all staff from the “Planta de Cultivos Marinos” (University of Cádiz) for the maintaining of animals used in these studies. We also acknowledge T. Katherine Tamai for the critical reading of the manuscript. This is the CEIMAR Journal Publication no. 11.

Declaration of Interest: This work was supported by grants from the Spanish MICINN (AGL2007-66507-C02-01 and AGL2010-22139-C03-03) and Junta de Andalucía (P06-AGR-01939) to José A. Muñoz-Cueto, and a predoctoral fellow of the Spanish MICINN (BES-2005-8629) to Águeda J. Martín-Robles.

The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the article.