Gerrard D E, Grant A L
Department of Animal Sciences, Purdue University, West Lafayette, IN 47907.
Domest Anim Endocrinol. 1994 Oct;11(4):339-47. doi: 10.1016/0739-7240(94)90005-1.
Double muscled (DM) cattle possess nearly 40% more muscle fibers than normal muscled (NM) beef or dairy cattle. Previous work showed that serum from DM fetuses stimulated proliferation of L6 myoblasts to a greater extent than serum from NM fetuses. Although the exact role of insulin-like growth factor-II (IGF-II) in the regulation of fetal myogenesis is unknown, it has been shown to serve as a autocrine-acting growth factor during terminal differentiation of myoblasts in mitogen-depleted culture media. Delay of IGF-II expression may alter the ultimate number of muscle fibers formed during fetal development. To investigate this, forty-seven skeletal muscle and twenty-nine liver samples were collected from NM fetuses representing fetuses grouped by crown-rump lengths (CRL) of < 20, 21-30, 31-40, 41-50, 51-60, 61-70 or > 70 cm. Twelve DM fetuses representing 20, 40, 50, and 85 cm were compared to NM groups with the same CRL. Total RNA preparations from these samples were subjected to northern and dot blot analysis using rat IGF-II and beta actin cDNAs and a human 28S rRNA oligomer. IGF-II transcripts of 4.5, 3.6, 2.75, 2.5, and 1.15 kilobases (kb) were detected in liver and muscle RNA from both DM and NM fetuses. Liver IGF-II expression increased (P < 0.05) in both DM and NM fetuses with CRL. Mean concentrations of muscle IGF-II mRNA initially increased (P < 0.05), then decreased (P < 0.05) with CRL in DM and NM fetuses. Muscle IGF-II mRNA was greater (P < 0.05) for NM fetuses compared to DM fetuses at 20 cm CRL, whereas at 53 cm CRL, DM muscle IGF-II was greater (P < 0.05) than that of NM fetuses. These results show that the maximum expression of muscle IGF-II is delayed in DM fetuses compared to NM fetuses. This delayed expression may play an explicit role in controlling myogenesis in the development of double muscle cattle.
双肌（DM）牛的肌纤维数量比正常肌肉（NM）的肉牛或奶牛多近40%。先前的研究表明，与NM胎儿的血清相比，DM胎儿的血清能更大程度地刺激L6成肌细胞的增殖。尽管胰岛素样生长因子-II（IGF-II）在胎儿肌生成调节中的确切作用尚不清楚，但已表明它在有丝分裂原耗尽的培养基中，成肌细胞终末分化过程中作为一种自分泌作用的生长因子。IGF-II表达的延迟可能会改变胎儿发育过程中形成的肌纤维的最终数量。为了对此进行研究，从NM胎儿中收集了47份骨骼肌样本和29份肝脏样本，这些胎儿按冠臀长度（CRL）分组为<20、21 - 30、31 - 40、41 - 50、51 - 60、61 - 70或>70厘米。将代表20、40、50和85厘米的12份DM胎儿与相同CRL的NM组进行比较。使用大鼠IGF-II和β - 肌动蛋白cDNA以及人28S rRNA寡聚物，对这些样本的总RNA制剂进行Northern印迹和斑点印迹分析。在DM和NM胎儿的肝脏和肌肉RNA中均检测到4.5、3.6、2.75、2.5和1.15千碱基（kb）的IGF-II转录本。随着CRL增加，DM和NM胎儿肝脏中的IGF-II表达均增加（P < 0.05）。在DM和NM胎儿中，肌肉IGF-II mRNA平均浓度最初随着CRL增加而增加（P < 0.05），然后下降（P < 0.05）。在CRL为20厘米时，NM胎儿的肌肉IGF-II mRNA比DM胎儿的更高（P < 0.05），而在CRL为53厘米时，DM胎儿的肌肉IGF-II比NM胎儿的更高（P < 0.05）。这些结果表明，与NM胎儿相比，DM胎儿中肌肉IGF-II的最大表达延迟。这种延迟表达可能在双肌牛发育过程中控制肌生成方面发挥明确作用。
