Hormones,
growth factors, and other regulatory proteins associated with the so-called
“somatotropic axis” are candidate markers for quantitative trait in farm
animals. The biological effect of growth hormone (GH) plays numerous importantand central physiological roles in the growth, metabolism, reproduction, immune
function, osmoregulation, and other physiological functions of fish and other vertebrates.
Growth hormone receptor (GHR) is the cell surface receptor for GH and is required
for GH to carry out its effects on target tissues. As a receptor, GHR mediates
the biological actions of GH on target cells by transducing the GH stimulating
signal across the cell membrane and subsequently inducing the transcription of
many genes, including IGF-I. Although there are few studies on GHR in fish, in
Atlantic salmon GHR appears to play a similar role within the somatotropic axis
as in humans and its differential expression is what mediates the cellular
response to GH plasma levels, and in particular the production of IGF.
The fish GHR gene has been successfully cloned and characterized in
several fish species such as gilthead sea bream (Sparus aurata), Atlantic
(Salmo salar) and masu salmon (Oncorhynchus masou), and rainbow
trout (Onchorhynchus mykiss). Significant associations have been
observed between GHR gene polymorphism and growth rates by PCR
restriction fragment polymorphism (RFLP) marker (using four restriction
enzymes) in 353 individual Cyprinus carpio fish.
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