Overview

Our research focuses on the endocrinology of and mechanisms that govern hydromineral balance, development and growth in vertebrates. We apply physiological, molecular and cellular approaches to define how hormones integrate information from the environment and genome to regulate processes of adaptation, growth, and more recently sex determination. Our studies utilize primarily fish, but also mammalian model systems.

The questions we address are mainly fundamental in nature, but our work on commercially valuable species has broad application to aquaculture and fisheries. The following represent the specific goals and ongoing projects in my laboratory:

Prolactin and growth hormone are pituitary hormones derived from a common ancestral gene and that are known to possess up to 300 known functions in vertebrates. They regulate virtually every aspect of physiology including osmoregulation, behavior, growth and metabolism, reproduction and immune function. The diversity and number of actions of prolactin and growth hormone is paralleled by the complexity with which the hormones are regulated.

We are examining the influence of osmotic pressure, ambient temperature, stress factors, growth factors and neuropeptide hormones on the secretion, synthesis and gene expression of prolactin and growth hormone. An understanding of how prolactin and growth hormone is controlled by abiotic and hormonal factors is central to defining how the two pituitary hormones enhance or impair hydromineral balance and promote growth. We are also interested in the functional genomics or gene networks that are activated or suppressed by the various regulators of pituitary prolactin and growth hormone. This research is funded by the National Science Foundation.

We are defining a novel mechanism by which steroids alter target cell activity. For decades it was widely assumed that steroids exert delayed (hours-days) effects on target cells through the regulation of gene expression and protein synthesis. However, we (and others) discovered that steroids may exert rapid, membrane effects typically associated with the fast actions of neurotransmitters and peptide hormones. Our studies are defining the stimulus-secretion coupling mechanism for novel non-genomic, membrane actions of glucocorticoids.

Specifically, we are assessing the signaling pathways by which the “stress hormone” cortisol rapidly suppresses prolactin secretion. This includes examination of critical second-messengers (phospholipase C, Ca2+ and cAMP), kinases linked to growth factor signaling, as well as the receptors that might transduce cortisol’s rapid effect on hormone secretion. These studies employ a combination of methods to study cell-signaling, including both cell and tissue culture, pharmacological manipulations, bioimaging, hormone receptor-binding, immunoassays, various biochemical assays and electrophysiology. This research is funded by the National Science Foundation.

We are examining the biology of sex determination in flounder species, whose control falls somewhere between that of humans (genotypic) and turtles (temperature-sensitive). Specifically, we study the plasticity of temperature-sensitive sex determination in flounder, its variation among latitudinal distinct populations (Mid-Atlantic versus Gulf of Mexico), and the mechanisms that underlie environmental and hormonal control of sex differentiation.

Along with our research to develop technologies for chromosomal set manipulations, these studies should allow:

1.) assessment of those abiotic/biotic parameters that may lead to skewed sex ratios in wild and hatchery-reared populations, and

2.) methods needed to produce only faster growing female fish needed for the cultivation of this high value fish.

Our studies should also provide critical information on control of sex determination and its evolution in vertebrates with different life history strategies. This research is funded by the Salstonstall-Kennedy Program (National Marine Fisheries Service/National Oceanic and Atmospheric Administration[NOAA]) and Sea Grant (NOAA).

Define the hormonal and immunological basis of compensatory or “catch-up” growth. This phenomenon of supra-accelerated growth is seen in virtually all plants and animals, including humans when alleviated of growth stunting conditions that result from various factors such as stress or poor nutrition. Our particular interests is understanding the role endocrine growth regulators (insulin-like growth factors) and their receptors and binding proteins play in mediating stunted, normal and compensatory growth. Funded by the United States Department of Agriculture and Sea Grant

We are also taking a functional genomic approach to determine if the protein and gene expression of growth regulators and their receptors and binding proteins are heritable in animals selected for poor or superior growth. The idea here is to identify those components of the endocrine growth axis that might be selected for in regulating growth performance. These investigations should ultimately provide instantaneous protein and gene growth biomarkers as well as methods to accelerate genetic breeding programs. Funded by the United States Department of Agriculture and Sea Grant.