Hummingbirds are very well adapted to sustain efficient and rapid metabolic shifts. They oxidize ingested nectar to directly fuel flight when foraging but have to switch to oxidizing stored lipids derived from ingested sugars during the night or long-distance migratory flights. Understanding how this organism moderates energy turnover is hampered by a lack of information regarding how relevant enzymes differ in sequence, expression, and regulation. To explore these questions, we generated a chromosome-scale genome assembly of the ruby-throated hummingbird (A. colubris) using a combination of long- and short-read sequencing, scaffolding it using existing assemblies. We then used hybrid long- and short-read RNA sequencing of liver and muscle tissue in fasted and fed metabolic states for a comprehensive transcriptome assembly and annotation. Our genomic and transcriptomic data found positive selection of key metabolic genes in nectivorous avian species and deletion of critical genes (SLC2A4, GCK) involved in glucostasis in other vertebrates. We found expression of a fructose-specific version of SLC2A5 putatively in place of insulin-sensitive SLC2A5, with predicted protein models suggesting affinity for both fructose and glucose. Alternative isoforms may even act to sequester fructose to preclude limitations from transport in metabolism. Finally, we identified differentially expressed genes from fasted and fed hummingbirds, suggesting key pathways for the rapid metabolic switch hummingbirds undergo.

中文翻译：

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对蜂鸟代谢通量的基因组见解


蜂鸟非常适合维持高效和快速的新陈代谢变化。它们在觅食时氧化摄入的花蜜，直接为飞行提供燃料，但在夜间或长途迁徙飞行时，必须转而氧化储存的脂质，这些脂质来源于摄入的糖。由于缺乏有关相关酶在序列、表达和调节方面如何不同的信息，阻碍了对这种生物体如何调节能量周转的理解。为了探索这些问题，我们结合长读长和短读长测序，生成了红宝石喉蜂鸟 ( A. colubris ) 的染色体规模基因组组装，并使用现有组装对其进行支架化。然后，我们对禁食和进食代谢状态下的肝脏和肌肉组织进行混合长读长和短读长 RNA 测序，以进行全面的转录组组装和注释。我们的基因组和转录组数据发现，食肉鸟类中关键代谢基因的正向选择以及其他脊椎动物中参与葡萄糖稳态的关键基因（ SLC2A4 、 GCK ）的缺失。我们发现果糖特异性版本的SLC2A5的表达可能取代了胰岛素敏感的SLC2A5 ，预测的蛋白质模型表明对果糖和葡萄糖都有亲和力。替代异构体甚至可能起到螯合果糖的作用，以排除代谢运输的限制。最后，我们鉴定了禁食和喂食蜂鸟的差异表达基因，这表明蜂鸟经历快速代谢转换的关键途径。