The Stability of the Transcriptome during the Estrous Cycle in Four Regions of the Mouse Brain

We analyzed the transcriptome of the C57BL/6J mouse hypothalamus, hippocampus, neocortex, and cerebellum to determine estrous cycle-specific changes in these four brain regions. We found almost 16,000 genes are present in one or more of the brain areas but only 210 genes, ~1.3%, are significantly changed as a result of the estrous cycle. The hippocampus has the largest number of differentially expressed genes (DEGs) (82), followed by the neocortex (76), hypothalamus (63), and cerebellum (26). Most of these DEGs (186/210) are differentially expressed in only one of the four brain regions. A key finding is the unique expression pattern of growth hormone (Gh) and prolactin (Prl). Gh and Prl are the only DEGs to be expressed during only one stage of the estrous cycle (metestrus). To gain insight into the function of the DEGs, we examined gene ontology and phenotype enrichment and found significant enrichment for genes associated with myelination, hormone stimulus, and abnormal hormone levels. Additionally, 61 of the 210 DEGs are known to change in response to estrogen in the brain. 50 genes differentially expressed as a result of the estrous cycle are related to myelin and oligodendrocytes and 12 of the 63 DEGs in the hypothalamus are oligodendrocyte- and myelin-specific genes. This transcriptomic analysis reveals that gene expression in the female mouse brain is remarkably stable during the estrous cycle and demonstrates that the genes that do fluctuate are functionally related. Hypothalamus, hippocampus, neocortex, and cerebellum mRNA from adult female C57BL/6J (B6) mice were analyzed by RNA sequencing of 3 biological replicates for each of the 4 stages of the estrous cycle using an Illumina HiSeq 2500本研究对C57BL/6J小鼠的下丘脑、海马体、新皮层及小脑的转录组进行分析，以明确这四个脑区中存在的动情周期特异性基因表达变化。我们在一个或多个脑区中检测到近16000个基因的表达，但其中仅约1.3%（210个基因）的表达量因动情周期发生显著改变。差异表达基因（differentially expressed genes, DEGs）的数量以海马体最多（82个），其次依次为新皮层（76个）、下丘脑（63个）与小脑（26个）。绝大多数差异表达基因（186/210）仅在四个脑区中的单个脑区呈现差异表达。本研究的一项关键发现为生长激素（growth hormone, Gh）与催乳素（prolactin, Prl）独特的表达模式：二者是仅在动情周期的单个阶段——动情后期（metestrus）——表达的差异表达基因。为深入解析差异表达基因的功能，我们开展了基因本体论（gene ontology, GO）与表型富集分析，结果发现与髓鞘形成、激素刺激及激素水平异常相关的基因存在显著富集。此外，210个差异表达基因中有61个已知可响应脑中雌激素的刺激而发生表达变化。另有50个与髓鞘及少突胶质细胞相关的基因因动情周期出现差异表达，而下丘脑的63个差异表达基因中，有12个为少突胶质细胞特异性及髓鞘特异性基因。本转录组学分析揭示：雌性小鼠脑中的基因表达在动情周期内整体极为稳定，且确实发生波动的基因均存在功能相关性。我们采用Illumina HiSeq 2500平台，对成年雌性C57BL/6J（B6）小鼠的下丘脑、海马体、新皮层及小脑的mRNA进行RNA测序，每个动情周期的四个阶段均设置3个生物学重复样本。