Zheng Xiaoxu, Reho John J, Wirth Brunhilde, Fisher Steven A
Division of Cardiovascular Medicine, School of Medicine, University of Maryland, Baltimore, Maryland;
Institute of Human Genetics, University of Cologne, Cologne, Germany; Institute for Genetics, University of Cologne, Cologne, Germany; and Center for Molecular Medicine Cologne, University of Cologne, Cologne, Germany.
Am J Physiol Cell Physiol. 2015 Feb 15;308(4):C289-96. doi: 10.1152/ajpcell.00304.2014. Epub 2014 Nov 26.
Diversity of smooth muscle within the vascular system is generated by alternative splicing of exons, yet there is limited understanding of its timing or control mechanisms. We examined splicing of myosin phosphatase regulatory subunit (Mypt1) exon 24 (E24) in relation to smooth muscle myosin heavy chain (Smmhc) and smoothelin (Smtn) alternative exons (Smmhc E6 and Smtn E20) during maturation of mouse mesenteric artery (MA) smooth muscle. The role of transformer 2β (Tra2β), a master regulator of splicing in flies, in maturation of arterial smooth muscle was tested through gene inactivation. Splicing of alternative exons in bladder smooth muscle was examined for comparative purposes. MA smooth muscle maturation began after postnatal week 2 and was complete at maturity, as indicated by switching to Mypt1 E24+ and Smtn E20- splice variants and 11-fold induction of Smmhc. Similar changes in bladder were complete by postnatal day 3. Splicing of Smmhc E6 was temporally dissociated from Mypt1 E24 and Smtn E20 and discordant between arteries and bladder. Tamoxifen-induced smooth muscle-specific inactivation of Tra2β within the first week of life but not in maturity reduced splicing of Mypt1 E24 in MAs. Inactivation of Tra2β causing a switch to the isoform of MYPT1 containing the COOH-terminal leucine zipper motif (E24-) increased arterial sensitivity to cGMP-mediated relaxation. In conclusion, maturation of mouse MA smooth muscle begins postnatally and continues until sexual maturity. TRA2β is required for specification during this period of maturation, and its inactivation alters the contractile properties of mature arterial smooth muscle.
血管系统中平滑肌的多样性是由外显子的可变剪接产生的，但对其发生时间或调控机制的了解有限。我们研究了在小鼠肠系膜动脉（MA）平滑肌成熟过程中，肌球蛋白磷酸酶调节亚基（Mypt1）外显子24（E24）的剪接与平滑肌肌球蛋白重链（Smmhc）和smoothelin（Smtn）可变外显子（Smmhc E6和Smtn E20）的关系。通过基因失活测试了果蝇剪接主调节因子transformer 2β（Tra2β）在动脉平滑肌成熟中的作用。为了进行比较，还研究了膀胱平滑肌中可变外显子的剪接情况。MA平滑肌成熟在出生后第2周开始，并在成熟时完成，表现为转换为Mypt1 E24 +和Smtn E20 -剪接变体以及Smmhc的11倍诱导。膀胱中的类似变化在出生后第3天完成。Smmhc E6的剪接在时间上与Mypt1 E24和Smtn E20分离，并且在动脉和膀胱之间不一致。在出生后第一周但不是在成熟时，他莫昔芬诱导的Tra2β平滑肌特异性失活降低了MA中Mypt1 E24的剪接。Tra2β失活导致转换为含有COOH末端亮氨酸拉链基序（E24 -）的MYPT1同工型，增加了动脉对cGMP介导的舒张的敏感性。总之，小鼠MA平滑肌的成熟在出生后开始并持续到性成熟。在此成熟期间，TRA2β是规格化所必需的，其失活会改变成熟动脉平滑肌的收缩特性。
