Minimal sex differences in gene expression in the rat superior olivary complex

A critical issue in large-scale gene expression analysis is the impact of sexually dimorphic genes, which may confound the results when sampling across sexes. Here, we assessed, for the first time, sex differences at the transcriptome level in the auditory brainstem. To this end, microarray experiments covering the whole rat genome were performed in the superior olivary complex (SOC) of 16-day-old Sprague-Dawley rats. Sexually dimorphic genes were identified using two criteria: a 2-fold change and a P-value < 0.05. Only 12 out of 41,374 probes (0.03%) showed sexually dimorphic expression. For comparison, pituitaries from 60-day-old female and male rats were analyzed, as this gland is known to display many sex-specific features. Indeed, almost 40 times more probes, i.e. 460 (1.1%), displayed sexual dimorphism. Quantitative RT-PCR confirmed 47 out of 48 microarray results from both tissues. Taking microarray and qRT-PCR data together, the expression of six genes (Prl, Eif2s3y, Gnrhr, Pomc, Ddx3y, Akr1c6) was higher in the male SOC, whereas two genes were upregulated in the female SOC (LOC302172, Xist). Four of these genes are sex-chromosome linked (Eif2s3y, Ddx3y, LOC302172, Xist). In summary, our data indicate only minor and negligible sex-specific differences in gene expression within the SOC at P16.