Cystathionine γ-lyase (CSE) is the last key enzyme in the transsulfuration pathway for the biosynthesis of cysteine from methionine in mammals, and catalyzes the hydrolysis of cystathionine into cysteine. Cysteine can be provided through diet; however, several investigators have suggested that infants may require dietary supplements of cysteine because of very low or undetectable CSE activity in their livers. We have previously shown that CSE levels are much lower in the livers and kidneys of fetal and infant mice than in those of adult mice, suggesting that the maternal supply of cysteine is important for the early development of mice. Here we examined changes of CSE expression in the livers and kidneys of dams during gestation and lactation. Hepatic enlargement was observed as early as gestational day 12.5 (G12.5) and thereafter became more prominent, whereas expression of CSE in the livers was found after postpartum day 1 (P1) and reached a peak at P14. The maintenance of lactation was essential for both hepatic enlargement and CSE expression. In contrast, kidneys gained weight only slightly during lactation while CSE expression in kidneys was markedly induced at G15.5 and then gradually declined through to P28. Serum concentrations of homocysteine (the precursor of cystathionine) were significantly lower in G18.5 dams than in virgins or G15.5 dams, suggesting that the expression of CSE in the kidneys contributes to the effective clearance of homocysteine during the late gestational stage.
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