Faculty of Veterinary Sciences, University of Sydney, Sydney, NSW 2006, Australia.
BMC Genomics. 2011 Aug 19;12:420. doi: 10.1186/1471-2164-12-420.
The thymus plays a critical role in the development and maturation of T-cells. Humans have a single thoracic thymus and presence of a second thymus is considered an anomaly. However, many vertebrates have multiple thymuses. The tammar wallaby has two thymuses: a thoracic thymus (typically found in all mammals) and a dominant cervical thymus. Researchers have known about the presence of the two wallaby thymuses since the 1800s, but no genome-wide research has been carried out into possible functional differences between the two thymic tissues. Here, we used pyrosequencing to compare the transcriptomes of a cervical and thoracic thymus from a single 178 day old tammar wallaby.
We show that both the tammar thoracic and the cervical thymuses displayed gene expression profiles consistent with roles in T-cell development. Both thymuses expressed genes that mediate distinct phases of T-cells differentiation, including the initial commitment of blood stem cells to the T-lineage, the generation of T-cell receptor diversity and development of thymic epithelial cells. Crucial immune genes, such as chemokines were also present. Comparable patterns of expression of non-coding RNAs were seen. 67 genes differentially expressed between the two thymuses were detected, and the possible significance of these results are discussed.
This is the first study comparing the transcriptomes of two thymuses from a single individual. Our finding supports that both thymuses are functionally equivalent and drive T-cell development. These results are an important first step in the understanding of the genetic processes that govern marsupial immunity, and also allow us to begin to trace the evolution of the mammalian immune system.
胸腺在 T 细胞的发育和成熟中起着关键作用。人类只有一个胸胸腺，而第二个胸腺的存在被认为是一种异常现象。然而，许多脊椎动物有多个胸腺。袋狸有两个胸腺：一个胸胸腺（通常存在于所有哺乳动物中）和一个占主导地位的颈胸腺。自 19 世纪以来，研究人员就已经知道袋狸有两个胸腺，但没有对这两个胸腺组织之间可能存在的功能差异进行全基因组研究。在这里，我们使用焦磷酸测序技术比较了来自一只 178 天大的袋狸的颈胸腺和胸胸腺的转录组。
我们表明，袋狸的胸胸腺和颈胸腺都显示出与 T 细胞发育相关的基因表达谱。两个胸腺都表达了介导 T 细胞分化不同阶段的基因，包括血液干细胞向 T 细胞系的最初定向、T 细胞受体多样性的产生和胸腺上皮细胞的发育。关键的免疫基因，如趋化因子也存在。非编码 RNA 的表达模式也相似。在两个胸腺之间检测到 67 个差异表达的基因，这些结果的可能意义将进行讨论。
这是首次比较单个个体的两个胸腺的转录组。我们的发现支持两个胸腺在功能上是等效的，并驱动 T 细胞的发育。这些结果是理解控制有袋动物免疫的遗传过程的重要的第一步，也使我们能够开始追踪哺乳动物免疫系统的进化。
