PHYSIOLOGY OF A BASAL VERTEBRATE, THE SEA LAMPREY (PETROMYZON MARINUS): OSMOREGULATION AND CORTICOSTEROID ACTION [thesis]

Ciaran A. S. Shaughnessy
2020
Lamprey represent the most basal living example of a vertebrate animal which regulates its internal fluid and ion homeostasis. This phylogenetic position among vertebrates makes lamprey an important model organism for understanding the basal state, and thus the evolution, of physiological systems such as the mechanisms of osmo- and ionoregulation and the endocrine factors controlling them. Sea lamprey (Petromyzon marinus) are an anadromous fish, migrating from freshwater (FW) to seawater (SW)
more » ... to seawater (SW) as juveniles, then returning back upstream as mature adults to spawn. Surviving this transition from a solute-poor FW environment to a solute-concentrated SW environment requires many changes to osmo- and ionoregulatory mechanisms, which are driven, in part, by signaling from corticosteroid hormones. Much of this dissertation examines the molecular mechanisms for osmo- and ionoregulation in the lamprey gill and intestine and how corticosteroids control osmoregulatory processes in these tissues. Additionally, effect of temperature on osmoregulation, and the corticosteroid response to handling and thermal stressors are also examined. I report the results of experiments that were designed to identify molecular and organismal processes driving physiological acclimation to FW or SW residence. Special attention was given to understanding the endogenous nature of sea lamprey physiology, particularly regarding the development of the ability to survive and osmoregulate in SW that occurs during the larvae-to-juvenile metamorphosis. In Chapter 1, I offer an introduction to basic sea lamprey biology and physiology, including background on osmoregulation and corticosteroid action in fishes. In Chapter 2, I functionally characterize a critical ion transporter in the gills of SW-acclimated fishes responsible for Cl- secretion, the Na+/K+/2Cl- cotransporter (NKCC1). I demonstrate that (i) a membrane-bound NKCC1 is upregulated in the gills of sea lamprey during metamorphosis in preparation [...]
doi:10.7275/17602749 fatcat:4zedallw65b7divzuvw6qkux2q