Progress 11/01/02 to 10/31/05
Outputs
Upon completion of this project we have determined that administration of chicken adrenocorticotropin (ACTH) can induce production of growth hormone (GH) prematurely during chicken embryonic development. We have defined the involvement of the mineralocorticoid receptor in glucocorticoid induction of GH. And we have identified a number of genes that are directly regulated by glucocorticoids in the chick embryonic pituitary gland. In the final year of the project we have completed analysis of glucocorticoid-regulated gene expression using cDNA microarrays. These arrays contain 14,053 unique cDNAs and represent nearly half of the chicken genome. Analysis of the microarray results indicated that 388 genes were induced or suppressed by glucocorticoids. These results were compared with those from cultures treated in the presence of cycloheximide to identify 26 genes that responded at 1.5 or 3 hours, prior to GH induction at 6 hours, and that were regulated directly by
corticosterone in the absence of protein synthesis. We consider the 26 genes identified as candidates for mediating glucocorticoid induction of GH gene expression.
Impacts
We have identified about 30 genes that are regulated by glucocorticoids in conjunction with induction of growth hormone in the chicken. This information is useful in future studies aimed at characterizing the mechanisms underlying growth regulation in chickens and in identification of markers for breeding of superior chickens.
Publications
- Bossis I, Porter TE (2003) Evaluation of glucocorticoid-induced growth hormone gene expression in embryonic pituitary cells using a novel in situ mRNA quantitation method. Mol Cell Endocrinol 201:13-23
- Liu L, Dean CE, Porter TE (2003) Thyroid hormones interact with glucocorticoids to affect somatotroph abundance in chicken embryonic pituitary cells in vitro. Endocrinology 144:3836-3841
- Jenkins SA, Ellestad LE, Porter TE (2003) Cloning and Characterization of a Novel Chicken Dexamethasone-Induced Ras-Related 1 (Dexras1) cDNA. Program 85th Annual Meeting of the Endocrine Society.
- Ellestad LE, Porter TE (2003) Cloning of a cDNA for the Chicken Glucocorticoid-Induced Leucine Zipper: Evidence for Multiple Variants in the 3' Untranslated Region. Program 85th Annual Meeting of the Endocrine Society.
- Malkiewicz SA, Porter TE (2003) Characterization of Glucocorticoid-Induced Early Response Genes in the Chicken Embryonic Pituitary Gland. Program 85th Annual Meeting of the Endocrine Society.
- Jenkins SA, Porter TE (2004) Ontogeny of the hypothalamo-pituitary-adrenocortical axis in the chicken embryo. Domest Anim Endocrinol 26:267-275
- Fu X, Porter TE (2004) Glucocorticoid induction of lactotrophs and prolactin gene expression in chicken embryonic pituitary cells: A response delayed relative to stimulated growth hormone production. Endocrinology 145:1322-1330
- Bossis I, Nishimura S, Muchow M, Porter TE (2004) Pituitary expression of type I and type II glucocorticoid receptors during chicken embryonic development and their involvement in growth hormone cell differentiation. Endocrinology 145:3523-3531
- Fu X, Nishimura S, Porter TE (2004) Evidence that lactotrophs do not differentiate directly from somatotrophs during chick embryonic development. J Endocrinol 183: 417-425
- Liu L, Porter TE (2004) Endogenous thyroid hormones modulate pituitary somatotroph differentiation during chicken embryonic development. J Endocrinol 180:45-53
- Heuck KA, Porter TE (2004) Somatotropin response to corticosterone (CORT) and triiodothyronine (T3) during chick embryonic development. Program 8th International Symposium on Avian Endocrinology.
- Porter TE (2005) Regulation of pituitary somatotroph differentiation by hormones of peripheral endocrine glands. Domest Anim Endocrinol 29:52-62
- Porter TE, Ellestad LE (2005) Gene expression profiling in the developing neuroendocrine system of the chick. In: Avian Endocrinology, Dawson A, Sharp PJ (Eds.), Narosa Publishing House, New Dehli
- Heuck KA, Proudman JA, Porter TE (2005) Involvement of Mineralocorticoid and Glucocorticoid Receptors in Glucocorticoid Regulation of Growth Hormone (GH) Secretion and Gene Expression during Embryonic Development. Program 87th Annual Meeting of the Endocrine Society.
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Progress 01/01/03 to 12/31/03
Outputs
Funding for this project began 18 months ago. The specific aims of this project and our progress toward completing each are as follows. 1.) Modulation of somatotroph abundance and post-hatch growth. We have evaluated and optimized chicken ACTH for its ability to induce GH cells in vivo. Chicken ACTH, human ACTH and corticosterone (CORT) are equally effective at prematurely inducing GH cells. The ability of these treatments to stimulate growth rate after hatch will be evaluated within the coming year. 2.) Comparison of somatotroph responses with pituitary gene expression. We have developed real time RT-PCR assays for quantification of pituitary GH, GR and MR mRNA levels during embryonic development. We are currently performing experiments to characterize changes in somatotroph abundance and responses to CORT, T3 and T4 during embryonic development. We have established a dual label immunofluorescence method for enumeration of GR and MR-expressing somatotrophs, and this
aim will be completed within the next 3 months. 3.) Identification of intermediate genes in CORT-induced GH gene expression Our efforts toward completing this aim have proven to be both productive and frustrating. We attempted to define CORT-regulated GH gene elements by DNA footprinting. However, no CORT-induced protected elements were found within the first 488 bp of the 5' flanking region of the GH gene. We have identified and cloned three CORT-induced early response genes (SGK, GILZ, and Dexras1). Our attempts to identify more by differential display were determined to be too difficult and frustrating, and this approach was dropped. We will screen for CORT-induced genes using our Del-Mar 14K Chicken Integrated Systems Microarrays within the next 9 months.
Impacts
Completion of the proposed experiments will better define the mechanisms underlying the production of growth hormone during chicken embryonic devlopment. New approaches to improving growth performance in poultry may be identified.
Publications
- Ellestad LE, Porter TE (2003) Cloning of a cDNA for the Chicken Glucocorticoid-Induced Leucine Zipper: Evidence for Multiple Variants in the 3' untranslated Region. Program 85th Annual Meeting of the Endocrine Society
- Jenkins SA, Ellestad LE, Porter TE (2003) Cloning and Characterization of a Novel Chicken Dexamethasone-Induced Ras-Related 1 (Dexras1) cDNA. Program 85th Annual Meeting of the Endocrine Society
- Malkiewicz SA, Porter TE (2003) Characterization of Glucocorticoid-Induced Early Response Genes in the Chicken Embryonic Pituitary Gland. Program 85th Annual Meeting of the Endocrine Society
- Heuck KA, Porter TE (2004) Somatotropin response to corticosterone (CORT) and triiodothyronine (T3) during chick embryonic development. Program 8th International Symposium on Avian Endocrinology
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