Section on Developmental Neuroscience, Laboratory of Cochlear Development, Division of Intramural Research, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, Maryland, United States of America.
Molecular Genomics Core Facility, Office of the Scientific Director, Intramural Research Program, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland, United States of America.
PLoS One. 2018 Oct 22;13(10):e0205883. doi: 10.1371/journal.pone.0205883. eCollection 2018.
The vertebrate pineal gland is dedicated to the production of the hormone melatonin, which increases at night to influence circadian and seasonal rhythms. This increase is associated with dramatic changes in the pineal transcriptome. Here, single-cell analysis of the rat pineal transcriptome was approached by sequencing mRNA from ~17,000 individual pineal cells, with the goals of profiling the cells that comprise the pineal gland and examining the proposal that there are two distinct populations of pinealocytes differentiated by the expression of Asmt, which encodes the enzyme that converts N-acetylserotonin to melatonin. In addition, this analysis provides evidence of cell-specific time-of-day dependent changes in gene expression. Nine transcriptomically distinct cell types were identified: ~90% were classified as melatonin-producing α- and β-pinealocytes (1:19 ratio). Non-pinealocytes included three astrocyte subtypes, two microglia subtypes, vascular and leptomeningeal cells, and endothelial cells. α-Pinealocytes were distinguished from β-pinealocytes by ~3-fold higher levels of Asmt transcripts. In addition, α-pinealocytes have transcriptomic differences that likely enhance melatonin formation by increasing the availability of the Asmt cofactor S-adenosylmethionine, resulting from increased production of a precursor of S-adenosylmethionine, ATP. These transcriptomic differences include ~2-fold higher levels of the ATP-generating oxidative phosphorylation transcriptome and ~8-fold lower levels of the ribosome transcriptome, which is expected to reduce the consumption of ATP by protein synthesis. These findings suggest that α-pinealocytes have a specialized role in the pineal gland: efficiently O-methylating the N-acetylserotonin produced and released by β-pinealocytes, thereby improving the overall efficiency of melatonin synthesis. We have also identified transcriptomic changes that occur between night and day in seven cell types, the majority of which occur in β-pinealocytes and to a lesser degree in α-pinealocytes; many of these changes were mimicked by adrenergic stimulation with isoproterenol. The cellular heterogeneity of the pineal gland as revealed by this study provides a new framework for understanding pineal cell biology at single-cell resolution.
脊椎动物的松果腺专门用于产生褪黑素激素，该激素在夜间增加以影响昼夜节律和季节性节律。这种增加与松果体转录组的剧烈变化有关。在这里，通过对约 17000 个单独的松果体细胞的 mRNA 进行测序，对大鼠松果体转录组进行了单细胞分析，其目的是对组成松果体的细胞进行分析，并研究存在两种由 Asmt 表达分化的不同松果体细胞群的假设，Asmt 编码将 N-乙酰血清素转化为褪黑素的酶。此外，该分析提供了细胞特异性昼夜依赖的基因表达变化的证据。鉴定出 9 种转录上不同的细胞类型：约 90%的细胞被归类为产生褪黑素的α-和β-松果体细胞（比例为 1:19）。非松果体细胞包括三种星形胶质细胞亚型、两种小胶质细胞亚型、血管和软脑膜细胞以及内皮细胞。α-松果体细胞与β-松果体细胞的区别在于 Asmt 转录本高出约 3 倍。此外，α-松果体细胞的转录组差异可能通过增加 Asmt 辅因子 S-腺苷甲硫氨酸的可用性来增强褪黑素的形成，这是由于 S-腺苷甲硫氨酸前体的产生增加所致，ATP。这些转录组差异包括氧化磷酸化转录组的水平高出约 2 倍，核糖体转录组的水平低约 8 倍，预计这将减少蛋白质合成对 ATP 的消耗。这些发现表明，α-松果体细胞在松果腺中具有特殊作用：有效地对β-松果体细胞产生和释放的 N-乙酰血清素进行 O-甲基化，从而提高褪黑素合成的整体效率。我们还鉴定了在七种细胞类型中发生在夜间和白天之间的转录组变化，其中大多数发生在β-松果体细胞中，在较小程度上发生在α-松果体细胞中；其中许多变化都被异丙肾上腺素的肾上腺素刺激所模拟。本研究揭示的松果体细胞的细胞异质性为理解松果体细胞生物学提供了一个新的单细胞分辨率框架。
