BMC Genomics 2009, 10:150 http://www.biomedcentral.com/1471-2164/10/150 JSF.uYigrCfu5a7rc,eCa25r7eBaLo/f6JcaorrdCio5m7y.YoAcymteicsefrom 12 week-old male A/ Surface area of cardiomyocytes from 12 week-old male A/J.YC57, C57BL/6J or C57.YA mice. All animals have undergone surgery (either sham or castration) at 4 weeks of age, and were treated with testosterone cypionate (either 0.5 mg or 2 mg/kg body weight) from 8 to 12 weeks of age. The figures represent values for individual animals scattered around the mean value of the group. **P < 0.01; ***P < 0.001. very different than their respective effects on the size of CMs. For instance, although post-pubertal testosterone had no effect on the size of CMs from C57.YA male mice, it affected the expression level of many cardiac genes in that strain, and even of a greater number of genes than in their C57BL/6J counterparts. This indicated that the lack of hypertrophic effects of post-pubertal testosterone on CMs from C57.YA was not the manifestation of an insen- sitivity of cells from this strain to androgens, but rather the result of a differential molecular response to the hor- mone. Likewise, despite the fact that the effect of chrY on the size of CMs was observed only in sham intact C57BL/ 6J mice but not in their CX counterparts, more cardiac genes showed chrY-dependent differential expression in CX than in sham intact animals. This indicated that the presence of post-pubertal testosterone was not required in order to observe an effect of chrY. Finally, in addition to the marginal effects of strain and surgery, we also tested for interaction between these two factors, which allowed us to identify within the genome 249 unique genes (here- after referred to as "interaction genes") whose expression was affected by CX (and thus by post-pubertal testoster- one) differentially according to the genetic origin of chrY (Additional file 1). Most interactions genes showed rather large differences in gene expression, as ~44% of them dis- played either strain-dependent differences or surgery- dependent changes were greater than 1.5 fold. To validate the results of the microarray analysis, we performed real- time RT-PCR quantifications for 6 of the interaction genes. The differences detected by RT-PCR were similar to those that had been detected with the microarray (Figure 3). To further determine 1) which particularly surgery group comprised genes where the strain-dependent differences in expression varied according to the surgery status, and 2) to which particular strain corresponded genes where the cFRaiesgatulr-artitemed3e)RT-PCR quantifications of 6 genes in the hearts of adult male C57BL/6J and C57.YA (either intact sham-operated of Real-time RT-PCR quantifications of 6 genes in the hearts of adult male C57BL/6J and C57.YA (either intact sham-operated of castrated). *P < 0.05; **P < 0.01; *P < 0.001 (Bonferroni-corrected post-hoc tests). Page 3 of 11 (page number not for citation purposes)