The Israeli Journal of Aquaculture - Bamidgeh 54(2), 2002
The Annual Dan Popper Symposium


DEVELOPMENT OF THE PINEAL MELATONIN-GENERATING SYSTEM
IN GILTHEAD SEABREAM (SPARUS AURATA)EMBYROS AND LARVAE


Galit Lisaey¹, Yoav Gothilf², Benny Ron¹*

1 Israel Oceanographic and Limnological Research, National Center for Mariculture, Fish Physiology Department, P.O.Box 1212, Eilat 88112, Israel
2 Department of Zoology, Tel Aviv University, Tel Aviv 69978, Israel


Abstract

Melatonin production is directly controlled by the activity of the enzyme serotonin-N -acetyltrans-ferase (AANAT) which, in turn, is regulated by the circadian clock. The circadian clock-regulation of AANAT activity differs from one species to another and could occur at the transcriptional, post-translational or both levels. In fish, the endogenous circadian clock is contained within the photoreceptive cells of the pineal gland and the retina. As a consequence, circadian rhythmicity of AANAT activity can be observed when these tissues are placed in culture. In this work, we investigated the very early development of seabream pineal photoreceptors and the circadian clock function by measuring melatonin, AANAT activity and sbAANAT-2 mRNA expression.

It has been shown that two AANAT genes, AANAT-1 and AANAT-2, with different expression patterns are present in the teleost species pike, trout, and zebrafish. We discovered that seabream also has two AANAT genes. Our investigation revealed that sbAANAT-1 is expressed only in the retina and sbAANAT-2 is expressed only in the pineal gland (data not shown). We then ascertained that the sbAANAT-2 mRNA is an effective marker for developmental studies of the pineal and retinal photoreceptor. The melatonin generating system is functional immediately following hatching in seabream larvae. There is a significant difference between "immediately after" (42 hpf), "before" (18 hpf) and "12 hours after" (54 hpf) hatching in the expression of the gene, enzyme activity and melatonin production. It is possible that the rhythms of sbAANAT expression are in different phases. Therefore, studying the differential regulation of these two related clock-controlled genes in seabream may provide valuable insights into the mechanism of the circadian clock.

*Corresponding author. Fax: 972-8-6375761, e-mail: ronbenny@agri.huji.ac.il

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