Guderley Helga, Joanisse Denis R, Mokas Sophie, Bilodeau Geneviève M, Garland Theodore
Département de biologie, Université Laval, Québec QC, Canada G1K 7P4.
Comp Biochem Physiol B Biochem Mol Biol. 2008 Mar;149(3):490-500. doi: 10.1016/j.cbpb.2007.11.012. Epub 2007 Dec 14.
Selective breeding of mice for high voluntary wheel running has favoured characteristics that facilitate sustained, aerobically supported activity, including a "mini-muscle" phenotype with markedly reduced hind limb muscle mass, increased mass-specific activities of oxidative enzymes, decreased % myosin heavy chain IIb, and, in the medial gastrocnemius, reduced twitch speed, reduced mass-specific isotonic power, and increased fatigue resistance. To evaluate whether selection has altered fibre type expression in mice with either "mini" or normal muscle phenotypes, we examined fibre types of red and white gastrocnemius. In both the medial and lateral gastrocnemius, the mini-phenotype increased activities of oxidative enzymes and decreased activities of glycolytic enzymes. In red muscle samples, the mini-phenotype markedly changed fibre types, with the % type I and type IIA fibres and the surface area of type IIA fibres increasing; in addition, mice from selected lines in general had an increased % type IIA fibres and larger type I fibres as compared with mice from control lines. White muscle samples from mini-mice showed dramatic structural alterations, with an atypical distribution of extremely small, unidentifiable fibres surrounded by larger, more oxidative fibres than normally present in white muscle. The increased proportion of oxidative fibres and these atypical small fibres together may explain the reduced mass and increased mitochondrial enzyme activities in mini-muscles. These and previous results demonstrate that extension of selective breeding beyond the time when the response of the selected trait (i.e. distance run) has levelled off can still modify the mechanistic underpinnings of this behaviour.
对小鼠进行高自主转轮行为的选择性育种，有利于那些促进持续的、有氧支持活动的特征，包括一种“迷你肌肉”表型，其具有明显减少的后肢肌肉质量、氧化酶的质量比活性增加、肌球蛋白重链IIb百分比降低，并且在内侧腓肠肌中，抽搐速度降低、质量比等张力量降低以及抗疲劳能力增加。为了评估选择是否改变了具有“迷你”或正常肌肉表型的小鼠的纤维类型表达，我们检查了红色和白色腓肠肌的纤维类型。在内侧和外侧腓肠肌中，迷你表型均增加了氧化酶的活性并降低了糖酵解酶的活性。在红色肌肉样本中，迷你表型显著改变了纤维类型，I型和IIA型纤维的百分比以及IIA型纤维的表面积增加；此外，与对照品系的小鼠相比，选择品系的小鼠总体上IIA型纤维的百分比增加且I型纤维更大。迷你小鼠的白色肌肉样本显示出显著的结构改变，存在一种非典型分布，即极小的、无法识别的纤维被比白色肌肉中正常存在的更大且更具氧化性的纤维所包围。氧化纤维比例的增加以及这些非典型的小纤维共同可能解释了迷你肌肉中质量的减少和线粒体酶活性的增加。这些结果以及之前的结果表明，在所选性状（即跑步距离）的反应趋于平稳之后继续进行选择性育种，仍然可以改变这种行为的机制基础。
