Simultaneous activation of genes encoding urea cycle enzymes and gluconeogenetic enzymes coincides with a corticosterone surge period before metamorphosis in Xenopus laevis
Simultaneous activation of genes encoding urea cycle enzymes and gluconeogenetic enzymes coincides with a corticosterone surge period before metamorphosis in Xenopus laevis
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DOI：
10.1111/dgd.12833
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发表时间：
2022-12
期刊：
影响因子：
4.6
通讯作者：
N. Konno
中科院分区：
文献类型：
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作者：
N. Konno
据推测，两栖类蝌蚪以氮代谢产物的形式排泄氨，但在变态过程中从排氨作用转变为排尿素作用。然而，它是未知的尿素是否发生或发挥功能的作用之前，变态。在此，从受精后5天（dpf）的47期爪蟾蝌蚪开始，在开始进食（45期，4 dpf）和变态（55期，32 dpf）之间，测量两种尿素循环酶（氨甲酰磷酸合成酶I [CPSI]和鸟氨酸转氨甲酰酶[OTC]）的mRNA表达水平。CPSI和OTC表达水平从第49期（12 dpf）开始显著增加。在第47阶段也检测到尿素排泄。一个短暂的皮质酮激增峰值在第48阶段以前的报道，支持皮质酮可以诱导CPSI表达的蝌蚪，在成年青蛙和哺乳动物中发现的假设。将46期蝌蚪暴露于合成糖皮质激素地塞米松（Dex，10-500 nM）3天。暴露于Dex的蝌蚪中CPSI mRNA的表达显著高于暴露于溶剂对照的蝌蚪。此外，糖皮质激素受体mRNA的表达增加在前变质期。除了CPSI和OTC mRNA上调外，三种致炎酶基因（葡萄糖6-磷酸酶、磷酸烯醇丙酮酸羧激酶和果糖-1，6-二磷酸酶1）的表达水平也随着尿素合成和排泄的开始而增加。这些结果表明，同时诱导的尿素循环和促凝酶与皮质酮激增发生前变态。变态前的这些代谢变化可能与变态所需的摄食和营养积累密切相关。
Amphibian tadpoles are postulated to excrete ammonia as nitrogen metabolites but to shift from ammonotelism to ureotelism during metamorphosis. However, it is unknown whether ureagenesis occurs or plays a functional role before metamorphosis. Here, the mRNA‐expression levels of two urea cycle enzymes (carbamoyl phosphate synthetase I [CPSI] and ornithine transcarbamylase [OTC]) were measured beginning with stage‐47 Xenopus tadpoles at 5 days post‐fertilization (dpf), between the onset of feeding (stage 45, 4 dpf) and metamorphosis (stage 55, 32 dpf). CPSI and OTC expression levels increased significantly from stage 49 (12 dpf). Urea excretion was also detected at stage 47. A transient corticosterone surge peaking at stage 48 was previously reported, supporting the hypothesis that corticosterone can induce CPSI expression in tadpoles, as found in adult frogs and mammals. Stage‐46 tadpoles were exposed to a synthetic glucocorticoid, dexamethasone (Dex, 10–500 nM) for 3 days. CPSI mRNA expression was significantly higher in tadpoles exposed to Dex than in tadpoles exposed to the vehicle control. Furthermore, glucocorticoid receptor mRNA expression increased during the pre‐metamorphic period. In addition to CPSI and OTC mRNA upregulation, the expression levels of three gluconeogenic enzyme genes (glucose 6‐phosphatase, phosphoenolpyruvate carboxykinase, and fructose‐1,6‐bisphosphatase 1) increased with the onset of urea synthesis and excretion. These results suggest that simultaneous induction of the urea cycle and gluconeogenic enzymes coincided with a corticosterone surge occurring prior to metamorphosis. These metabolic changes preceding metamorphosis may be closely related to the onset of feeding and nutrient accumulation required for metamorphosis.