Melatonin is required for asymmetric gene expression in the zebrafish habenular nuclei

NANCY HERNANDEZ DE BORSETTI; JOSHUA T. GAMSE

Nashville, TN

Encuentro; Retreat XII, Society of Biological Development.; 2008

Vanderbilt University. Developmental Biology Department

Melatonin is required for asymmetric gene expression in the zebrafish habenular nuclei Nancy Hernandez de Borsetti and Joshua Gamse In nature, organisms coordinate their activities and biological processes with the day-night cycle to take advantage of the environmental conditions. In vertebrates, the hormone melatonin secreted by the pineal gland transmits temporal information to the organism. Photoperiod regulates rhythmic melatonin production in the pineal gland, but not if embryos are raised in constant darkness. Melatonin was also demonstrated to accelerate the development of zebrafish embryos. Here, we demonstrate that different light conditions result in altered habenular gene expression patterns in zebrafish embryos. Exposure to DD (constant darkness) delayed expression of the asymmetrically expressd genes: lov (leftover) and ron (right on) in the habenular nuclei of the epithalamus when compared to embryos maintained in LD condition (Light:Dark cycles). However, gene expression in the pineal gland and parapineal organ remains unaffected in both DD and LD conditions. We also demonstrate that the effect of light observed in the habenular gene expression is mediated by melatonin. Embryos exposed to LD conditions and treated with luzindole (a melatonin receptor antagonist) also exhibited delayed habenular gene expression similar to DD exposed embryos. Conversely, embryos exposed to DD conditions and treated with exogenous melatonin are rescued to the LD habenular gene expression pattern. Therefore, the melatonin signaling pathway plays a role during asymmetric development of the brain by providing temporal information for the appropriate gene expression to take place.