Collaborative Research: The Evolution of Endocrine Function; Discovering the Hormonal Control of Osmoregulation in Basal Vertebrates

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All living organisms must regulate their internal salt and water content to function routinely and survive. In more complex animals, such as vertebrates, hormones and the receptors to which they bind are critical signaling molecules involved in regulation of salt and water transport. Fish are in direct contact with water, and they must actively take up salts from freshwater and actively secrete them in seawater to be able to regulate internal salt concentrations. To date research on the hormonal control of salt regulation has been limited to studies on advanced fish species. This project will examine the hormonal control of salt regulation in two basal vertebrates, lamprey eel and sturgeon. The researchers will examine how growth hormone and prolactin, two hormones secreted by the pituitary gland, and their receptors are altered by external salinity. This research will determine the effect of these hormones on the ability of lamprey and sturgeon to tolerate changes in external salinity. The results of these studies will yield insights about the functional evolution of these hormones, which in turn could be applied to enhancing agricultural production of fish and management of invasive lamprey. The results will be rapidly transferred to textbooks in comparative endocrinology and physiology, published in peer-reviewed journals, and shared at scientific meetings. Studies supported by this award will investigate the functional evolution of osmoregulatory hormones in aquatic vertebrates. Our current understanding of the hormonal control of osmoregulation in aquatic vertebrates comes almost entirely from advanced bony fish (teleosts), and there is no information on how pituitary hormones control osmoregulation in basal vertebrates. It is now well-established that prolactin (PRL) is critical for survival of most teleosts in freshwater (FW) and that growth hormone (GH), at least in some lineages, promotes osmoregulation in seawater (SW). Lamprey, as basal vertebrates, and chondrosteans (including sturgeon), as basal bony fish, have the same osmoregulatory strategy as teleosts (namely, maintaining nearly constant levels of plasma ions irrespective of external salinity), yet there is currently no information on whether PRL or GH play a role in osmoregulation of either lamprey or chondrosteans. There is strong evidence that lamprey possess only one member of the PRL/GH family of pituitary hormones (GH), making them especially critical for these studies. Our specific aims are: 1) to determine the response of GH and GH receptor to salinity change in lamprey; 2) to determine the osmoregulatory actions of GH in lamprey; and 3) to determine the osmoregulatory roles of GH and PRL in sturgeon. For each species we will examine the time course of physiological and endocrine responses to reciprocal transfers between FW and SW. We will utilize recombinant technology to make lamprey GH in order to develop homologous radioimmuno- and radioreceptor- assays, and determine its osmoregulatory actions in vivo and in vitro.