Genetic studies of stress response in zebrafish.

Deepak Ailani1,2, Pradeep Lal1,2, Akira Muto1,2, Koichi Kawakami1,2. 1) Division of Molecular and Developmental Biology, National Institute of Genetics, Mishima, Japan; 2) Department of Genetics, Graduate University for Advanced Studies (SOKENDAI), Mishima, Japan.

The hypothalamic-pituitary-adrenal (HPA) axis is the major endocrine stress axis of vertebrates. Mammalian studies have shown that various brain structures such as limbic system structures and brainstem nuclei are involved in the regulation of HPA axis and glucocorticoid release. However, the neural mechanisms of such regulation are still largely unknown. To address this question, we aim to identify functional neural circuits regulating HPA axis and stress response through genetic analysis using zebrafish. We used a swimming behavior of an isolated fish when introduced into a novel tank as a measure of anxiety. Anxious fish spend more time near the bottom. Our enhancer trap and gene trap screens generated several transgenic zebrafish which express Gal4 in the specific regions of the adult zebrafish brain. Through systematic inactivation of Gal4 expressing neurons using UAS: neurotoxin fish, we analyzed the behavior in a novel tank, and identified a transgenic line that showed reduced stress response. In this line, Gal4 was expressed in the putative eminentia thalamus (EmT) in the adult brain. Anatomical studies have proposed EmT as functional homologue of mammalian Bed Nucleus of the Stria Terminalis (BNST), which is an important regulator of HPA axis in mammals. Thus, our study revealed a key neural population in adult zebrafish brain that regulates stress response. To understand the function of EmT in stress response, we are currently aiming to conduct anatomical and molecular studies. We are also establishing a system to study stress response in zebrafish larva that enables functional imaging using optogenetic tools.