Geiger Paige C, Bailey Jeffrey P, Mantilla Carlos B, Zhan Wen-Zhi, Sieck Gary C
Department of Physiology and Biomedical Engineering, Mayo Clinic College of Medicine, 200 First St. SW, Rochester, MN 55905, USA.
J Appl Physiol (1985). 2006 Dec;101(6):1546-55. doi: 10.1152/japplphysiol.00221.2006. Epub 2006 Jul 27.
During early postnatal development in rat diaphragm muscle (Dia(m)), significant transitions in myosin heavy chain (MHC) isoform expression occur that are associated with fiber growth and increased MHC protein. At present, there is no direct information regarding the transcriptional regulation of MHC isoform expression during postnatal Dia(m) development. We hypothesized postnatal changes in MHC isoform mRNA expression are followed by concomitant changes in MHC protein expression. The Dia(m) was removed at postnatal days 0, 14, 28, and 84 (adult). MHC mRNA expression was determined by real-time RT-PCR. MHC protein expression was determined by SDS-PAGE. There was a significant effect of postnatal age on MHC isoform mRNA and protein expression. At birth, the MHC(Neo) isoform accounted for 28% of MHC mRNA and 54% of total MHC protein. By postnatal day 14, MHC(Neo) mRNA and protein increased significantly, and both decreased significantly by day 28, consistent with transcriptional control of the expression of this developmental isoform. By postnatal day 28, there were minimal changes in mRNA expression for MHC(Slow) and MHC(2X), yet protein expression increased significantly. MHC(2A) mRNA and protein expression did not change during this time. Thus changes in MHC protein expression did not follow (or parallel) changes in MHC mRNA for the adult MHC isoforms. The present findings indicate that changes in MHC expression in the developing rat Dia(m) are not driven solely by changes in mRNA expression. Knowledge of isoform-specific MHC mRNA expression only yields predictive information on MHC protein expression for the MHC(Neo) isoform.
在大鼠膈肌（Dia(m)）出生后的早期发育过程中，肌球蛋白重链（MHC）亚型表达会发生显著转变，这与纤维生长和MHC蛋白增加有关。目前，关于出生后Dia(m)发育过程中MHC亚型表达的转录调控尚无直接信息。我们假设出生后MHC亚型mRNA表达的变化会伴随MHC蛋白表达的相应变化。在出生后第0天、14天、28天和84天（成年）切除Dia(m)。通过实时RT-PCR测定MHC mRNA表达。通过SDS-PAGE测定MHC蛋白表达。出生后年龄对MHC亚型mRNA和蛋白表达有显著影响。出生时，MHC(Neo)亚型占MHC mRNA的28%和总MHC蛋白的54%。到出生后第14天，MHC(Neo) mRNA和蛋白显著增加，到第28天两者均显著下降，这与该发育亚型表达的转录控制一致。到出生后第28天，MHC(Slow)和MHC(2X)的mRNA表达变化极小，但蛋白表达显著增加。在此期间，MHC(2A)的mRNA和蛋白表达没有变化。因此，对于成年MHC亚型，MHC蛋白表达的变化并不跟随（或平行于）MHC mRNA的变化。目前的研究结果表明，发育中的大鼠Dia(m)中MHC表达的变化并非仅由mRNA表达的变化驱动。仅了解亚型特异性MHC mRNA表达只能得出关于MHC(Neo)亚型MHC蛋白表达的预测信息。
