Crucial role of zebrafish prox1 in hypothalamic catecholaminergic neurons development

Here we report that, in zebrafish, prox1 is widely expressed in several districts of the Central Nervous System (CNS). Specifically, we evidenced prox1 expression in a group of neurons, already positive for otp1, located in the hypothalamus at the level of the posterior tuberculum (PT). Prox1 knock-down determines the severe loss of hypothalamic catecholaminergic (CA) neurons, identified by tyrosine hydroxylase (TH) expression, and the synergistic prox1/otp1 overexpression induces the appearance of hypothalamic supernumerary TH-positive neurons and ectopic TH-positive cells on the yolk epitelium.Our findings indicate that prox1 activity is crucial for the proper development of the otp1-positive hypothalamic neuronal precursors to their terminal CA phenotype.The catecholaminergic neurons of the CNS of vertebrates participate in a wide variety of tasks, including motor coordination, mood regulation, and cognitive function, among others. Neurotransmitters catecholamines (CA), namely Dopamine (DA), Adrenaline (AD), and Noradrenaline (NA), are neuroactive molecules that exert strong influence on vertebrates behavior [1] and serve a variety of central and peripheral functions [2].Embryological studies indicate that several extracellular signals, as Hedgehog and FGF, are vital to define the development of the prosencephalic CA neurons [3-7]. The homeodomain transcription factor Orthopedia (Otp), regulated by such signaling pathways [8], is crucial in restricting the fate of multiple classes of secreting neurons in the neuroendocrine hypothalamus of vertebrates [9,10]. Specifically, Otp is required for the correct differentiation of the CA neurons positioned in the zebrafish Posterior Tuberculum (PT) and hypothalamus [8,11]. Despite all these evidences, the role of specific transcription factors leading to the proper differentiation of the hypothalamic CA neurons remains largely unclear [7].Prox1 homeobox gene is the vertebrate homologous of prospero in Drosophila melanogas