Whole genome microarray analysis of growth hormone induced genes in bone

Growth hormone (GH) is important in the development and maintenance of bone; however the IGF-dependent and -independent molecular pathways involved remain to be established. We used microarray analysis to identify genes acutely regulated by GH, in the bones of four week old GH-deficient mice at 6 or 24 hours following a single injection of GH (4 mg/kg body wt) or PBS (n = 6/group). 6,160 genes were differentially expressed at P = 0.05 and 17% of these genes were identified at both time points. Several of the 201 genes that were up or down regulated at > 2 fold at 6 and/or 24 hours (P = 0.01) were expressed sequence tags, transcription factors, or signaling genes. In conclusion, GH caused acute changes in several novel genes, suggesting that many GH-induced signaling pathways and target genes remain to be discovered Keywords: GH injection induced gene expression, time course We used 4 week old C57BL/6J-Ghrhr [GHRHR gene disruption, allele name little (lit/lit)] mice for the microarray analysis. Twelve lit/lit mice were treated with a single injection of GH (4 mg/kg body weight), and 12 lit/lit mice were treated with PBS (controls). At 6 hours after injection, 6 mice each from the GH and PBS groups were euthanized by CO2 inhalation for sample preparation. RNA from two animals within each group was pooled together, generating three samples in each group. The same procedure was applied for the remaining half of the animals at 24 hours after injection. Therefore, there were a total of six replicates in each group (3 replicates at 6 hrs and 3 at 24 hrs)