Our objective is to understand how the endocrine system enables animals to thrive in dynamic environments.

Vertebrate endocrine systems are key controllers of the physiological processes that maintain homeostasis. Hormones are secreted from specialized cells and glands in response to dynamic external and/or internal conditions. These changes in hormone levels initiate adaptive responses aimed at returning the organism to homeostasis. Our research seeks to build a mechanistic understanding of how the endocrine system matches adaptive phenotypes with environmental circumstances.

 

Fishes experience significant challenges to maintaining homeostasis in the presence of large, and sometimes variable, osmotic and salt gradients with the external environment. In turn, they have evolved efficient mechanisms for detecting changes in internal and external salt conditions to initiate subsequent physiological responses. We leverage a variety of fish models (e.g., Mozambique tilapia, Atlantic salmon, mummichog, and zebrafish) that allow us to unravel how cellular and molecular processes underlie the physiology, development, and natural histories of animals residing in dynamic environments.

 

The first major theme of our research is to understand how pituitary hormones regulate organs that maintain hydromineral balance of the organism, namely the gill, kidney, urinary bladder, and gastrointestinal tract. We are particularly focused on identifying ion pumps, transporters, and channels regulated by prolactin signaling (see Breves et al., 2014 and Breves et al., 2020). Furthermore, specialized ion-transporting cells within the gill, coined "ionocytes", mount osmotic stress responses when exposed to changes in environmental salinity. We are currently investigating the interplay between cellular stress responses and systemic prolactin signaling to further contribute mechanistic insight into how hormones control vertebrate epithelial tissues.

 

The sensitivity of prolactin-secreting cells of the tilapia pituitary gland to variations in extracellular osmolality enables investigations into how osmoreception underlies adaptive patterns of hormone secretion. While prolactin is firmly established as a necessary factor for osmoregulation in freshwater environments, it remains unknown how osmoreceptive processes orchestrate the expression of multiple prolactin-encoding genes. The second major theme of our research is to therefore link molecular aspects of cellular osmoreception with the regulatory control of prolactin gene promoters (see Seale et al., 2020). Based on our findings, other vertebrate genomes can be searched for essential promoter regions and/or transcription factors that respond to changes in extracellular osmolality.

 

Finally, the third major theme of our research is to determine how the somatotropic axis (the growth hormone/insulin-like growth-factor system) matches growth patterns with environmental conditions. More specifically, we focus on how stressors, nutrition, salinity, and xenobiotics modulate the expression of insulin-like growth-factor binding proteins in Atlantic salmon and tilapia (see Breves et al., 2018, Breves et al., 2020, and this short animation). Atlantic salmon life-history transitions are deeply interconnected with somatic growth patterns and body size underlies overall fitness at key stages. A nuanced understanding of how growth is regulated equips physiologists to more precisely infer the growth patterns of wild fish and to optimize restoration strategies for endangered populations.