Department of Animal Biology, School of Integrative Biology, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA.
J Exp Zool B Mol Dev Evol. 2012 Jun;318(4):279-93. doi: 10.1002/jez.b.22444.
Proper regulation of growth is essential to all stages of life, from development of the egg into an embryo to the maintenance of normal cell cycle progression in adults. However, despite growth's importance to basic biology and health, little is known about how mammalian growth is regulated. In this study, we investigated the molecular basis of the highly disparate growth of opossum fore- and hind limbs in utero. We first used a novel, opossum-specific microarray to identify several growth-related genes that are differentially expressed in opossum fore- and hind limbs of comparable developmental stages. These genes included Igf1. Given Igf1's role in the growth of other systems, we further investigated the role of Igf1 in opossum limb growth. Supporting the microarray results, RT-PCR indicated that Igf1 levels are approximately two times higher in opossum fore- than hind limbs. Consistent with this, while Igf1 transcripts were readily detectable in opossum forelimbs using whole-mount in situ hybridization, they were not detectable in opossum hind limbs. Furthermore, opossum limbs treated with exogenous Igf1 protein experienced significantly greater cellular proliferation and growth than control limbs in vitro. Taken together, results suggest that the differential expression of Igf1 in developing opossum limbs contributes to their divergent rate of growth, and the unique limb phenotype of opossum newborns. This study establishes the opossum limb as a new mammalian model system for study of organ growth.
适当的生长调控对于生命的各个阶段都是至关重要的，从卵子发育成胚胎到维持成人正常的细胞周期进程。然而，尽管生长对基础生物学和健康非常重要，但人们对哺乳动物的生长调控知之甚少。在这项研究中，我们研究了负鼠前肢和后肢在子宫内高度不同的生长的分子基础。我们首先使用一种新的、专门针对负鼠的微阵列来鉴定出几个在发育阶段相似的负鼠前肢和后肢中差异表达的与生长相关的基因。这些基因包括 Igf1。鉴于 Igf1 在其他系统生长中的作用，我们进一步研究了 Igf1 在负鼠肢体生长中的作用。支持微阵列结果，RT-PCR 表明 Igf1 在负鼠前肢中的水平大约是后肢的两倍。与这一结果一致的是，虽然使用整体原位杂交在负鼠前肢中可以轻易地检测到 Igf1 转录本，但在负鼠后肢中却无法检测到。此外，体外给予外源性 Igf1 蛋白的负鼠肢体经历了比对照肢体显著更高的细胞增殖和生长。总之，研究结果表明，Igf1 在发育中的负鼠肢体中的差异表达有助于其不同的生长速度，并导致负鼠新生儿独特的肢体表型。这项研究确立了负鼠肢体作为研究器官生长的新的哺乳动物模型系统。
