ABSTRACT: Several processes governing growth and metabolism are regulated by the neuroendocrine system, particularly the trophic hormones produced in the anterior pituitary gland. However, many of the differences that exist in pituitary gene expression and functional gene networks associated with divergent growth characteristics are still largely unknown. Using the Del-Mar 14K Chicken Integrated Systems microarray, this experiment evaluated global gene expression in the anterior pituitary gland during the first 7 weeks of post-hatch growth in two lines of chickens genetically selected for high growth (HG) or low growth (LG) at SRA-INRA, France. The HG and LG chickens differ in body weight, abdominal fat content, and plasma hormone and metabolite levels, making them a valuable model for both biomedical and agricultural traits. Amplified total RNA extracted from individual anterior pituitary glands collected from 4 birds from each line at each age (n=4) was produced. Cy-3 labeled cDNA from these samples was hybridized with an aliquot of Cy-5 labeled cDNA made from a pool of total RNA from all 32 samples. Data were analyzed as log2-(Cy3intensity (norm)/Cy5intensity (raw)) by two-way ANOVA using a linear mixed model procedure (PROC MIXED; SAS institute Inc., Cary, NC), and a total of 2,310 spots were significantly different (P<0.05) by line (1,100), age (1,058), or the line-by-age interaction (353). Of these, we identified 291 spots representing 263 genes as differentially expressed between HG and LG birds, where there was a >160% difference between the highest expression in one line and the lowest expression in the other and a significant line-by-age (110) or line (181) effect. Four anterior pituitary hormones were contained in this set of differentially expressed genes: thyroid-stimulating hormone ?-subunit, luteinizing hormone ?-subunit, and follicle-stimulating hormone ?-subunit mRNA levels were higher in the HG line; and growth hormone mRNA was elevated in the LG line. Pathway analysis revealed differences in expression between HG and LG lines associated with molecular transport, endocrine system development and function, organ and tissue morphology, and cellular compromise. Potential alteration in pituitary function between the two lines was highlighted in a network containing genes associated with hormone expression and secretion, as well as those potentially involved in pituitary gland morphology and vascularization.
