REGULATION OF GROWTH HORMONE PRODUCTION IN BROILER CHICKEN EMBRYOS

Multiple hormones regulate growth in chickens. Among these, growth hormone (GH) is essential for normal body weight gain and muscle growth. The adrenal glucocorticoid corticosterone (CORT) induces GH cell differentiation during normal chicken embryonic development, and in ovo administration of CORT can induce premature GH production and stimulate post-hatch growth. CORT interacts with thyroid hormones to regulate embryonic GH production. Thus, future selection of breeding stock based on markers within the corticotropic, thyrotropic, and somatotropic axes has potential for improving growth and feed efficiency through modulating endogenous CORT, T3, and GH production and their target tissue responses. However, the broader effects of embryonic CORT and GH on post-hatch metabolism and gene expression within the somatotropic, corticotropic, and thyrotropic axes are not known. Furthermore, we have yet to define all of the transcription factors required for CORT induction of GH during embryonic development.The Specific Aims of this proposal are to:Determine effects of in ovo administration of CORT on mRNA levels for major components of the hypothalamo-pituitary somatotropic, corticotropic, and thyrotropic axes.Define effects of embryonic CORT treatment and premature induction of GH on indicators of adipose tissue function during posthatch development.Identify novel regulatory elements upstream of the GH transcription start site and their DNA-binding transcription factors.