Urea cycle enzymes and urea excretion during the development and metamophosis of Xenopus laevis

Balinsky, J.B.; Choritz, E.L.; Coe, C.G.L.; Schans, Gerda S. van der

doi:10.1016/0010-406x(67)90165-x

Cited by 20 publications

(1 citation statement)

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“…The shift from ammonotelic to ureotelic metabolism during amphibian metamorphosis is closely related to the water conservation required for the transition from aquatic tadpoles to terrestrial adults (Bray, 1985). The switch in the nitrogen‐metabolism pathway during metamorphosis is caused by the increased expression and activity of urea cycle enzymes in the liver (Balinsky et al, 1967; Galton et al, 1991; Morris Jr., 1987). Many findings have demonstrated that urea cycle enzymes are induced and activated during spontaneous and TH‐induced metamorphosis in amphibians (Atkinson et al, 1998; Balinsky, Dicker, Elliott, 1972; Balinsky, Coetzer, & Mattheyse, 1972; Xu et al, 1993).…”

Section: Introductionmentioning

confidence: 99%

Simultaneous activation of genes encoding urea cycle enzymes and gluconeogenetic enzymes coincides with a corticosterone surge period before metamorphosis in Xenopus laevis

Konno

2022

Dev Growth Differ

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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.

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