Department of Cellular and Molecular Physiology, Pennsylvania State University College of Medicine, PO Box 850, 500 University Drive, Hershey, PA 17033, USA.
Amino Acids. 2012 Feb;42(2-3):495-505. doi: 10.1007/s00726-011-1028-6. Epub 2011 Aug 2.
A composite cytomegalovirus-immediate early gene enhancer/chicken β-actin promoter (CAG) was utilized to generate transgenic mice that overexpress human spermidine synthase (SpdS) to determine the impact of elevated spermidine synthase activity on murine development and physiology. CAG-SpdS mice were viable and fertile and tissue SpdS activity was increased up to ninefold. This increased SpdS activity did not result in a dramatic elevation of spermidine or spermine levels but did lead to a 1.5- to 2-fold reduction in tissue spermine:spermidine ratio in heart, muscle and liver tissues with the highest levels of SpdS activity. This new mouse model enabled simultaneous overexpression of SpdS and other polyamine biosynthetic enzymes by combining transgenic animals. The combined overexpression of both SpdS and spermine synthase (SpmS) in CAG-SpdS/CAG-SpmS bitransgenic mice did not impair viability or lead to overt developmental abnormalities but instead normalized the elevated tissue spermine:spermidine ratios of CAG-SpmS mice. The CAG-SpdS mice were bred to MHC-AdoMetDC mice with a >100-fold increase in cardiac S-adenosylmethionine decarboxylase (AdoMetDC) activity to determine if elevated dcAdoMet would facilitate greater spermidine accumulation in mice with SpdS overexpression. CAG-SpdS/MHC-AdoMetDC bitransgenic animals were produced at the expected frequency and exhibited cardiac polyamine levels comparable to MHC-AdoMetDC littermates. Taken together these results indicate that SpdS levels are not rate limiting in vivo for polyamine biosynthesis and are unlikely to exert significant regulatory effects on cellular polyamine content and function.
利用复合巨细胞病毒即时早期基因增强子/鸡β-肌动蛋白启动子（CAG）生成了过表达人精脒合酶（SpdS）的转基因小鼠，以确定升高的精脒合酶活性对小鼠发育和生理学的影响。CAG-Spds 小鼠具有活力和繁殖力，组织 SpdS 活性增加了 9 倍。这种 SpdS 活性的增加并没有导致精脒或精胺水平的显著升高，但确实导致心脏、肌肉和肝脏组织中精胺：精脒比率降低 1.5-2 倍，而 SpdS 活性最高。这种新的小鼠模型通过组合转基因动物，使 SpdS 和其他多胺生物合成酶同时过表达。在 CAG-Spds/CAG-Spms 双转基因小鼠中同时过表达 SpdS 和精脒合酶（SpmS）并没有损害活力或导致明显的发育异常，而是使 CAG-Spms 小鼠升高的组织精胺：精脒比率正常化。将 CAG-Spds 小鼠与 MHC-AdoMetDC 小鼠杂交，后者心脏 S-腺苷甲硫氨酸脱羧酶（AdoMetDC）活性增加了 100 多倍，以确定升高的 dcAdoMet 是否会促进 SpdS 过表达小鼠中精脒的积累。以预期的频率产生了 CAG-Spds/MHC-AdoMetDC 双转基因动物，并表现出与 MHC-AdoMetDC 同窝仔相似的心脏多胺水平。总之，这些结果表明 SpdS 水平在体内不是多胺生物合成的限速因素，不太可能对细胞多胺含量和功能产生显著的调节作用。
