Gaunt S J, Dean W, Sang H, Burton R D
Department of Development and Genetics, The Babraham Institute, Babraham, Cambridge CB2 4AT, UK.
Mech Dev. 1999 Apr;82(1-2):109-18. doi: 10.1016/s0925-4773(99)00018-0.
Transposition of anatomical structures along the anteroposterior axis has been a commonly used mechanism for changing body proportions during the course of evolutionary time. Earlier work (Gaunt, S.J., 1994. Conservation in the Hox code during morphological evolution. Int. J. Dev. Biol. 38, 549-552; Burke, A.C., Nelson, C.E., Morgan, B.A., Tabin, C., 1995. Hox genes and the evolution of vertebrate axial morphology. Development 121, 333-346) showed how transposition in mesodermal derivatives (vertebrae) could be attributed to transposition in the expression of Hox genes along the axial series of somites. We now show how transposition in the segmental arrangement of the spinal nerves can also be correlated with shifts in the expression domains of Hox genes. Specifically, we show how the expression domains of Hoxa-7, a-9 and a-10 in spinal ganglia correspond similarly in both mouse and chick with the positions of the brachial and lumbosacral plexuses, and that this is true even though the brachial plexus of chick is shifted posteriorly, relative to mouse, by seven segmental units. In spite of these marked species differences in the boundaries of Hoxa-7 expression, cis regulatory elements located up to 5 kb upstream of the chick Hoxa-7 gene showed much functional and structural conservation with those described in the mouse (Puschel, A.W., Balling, R., Gruss, P., 1991. Separate elements cause lineage restriction and specify boundaries of Hox-1.1 expression. Development 112, 279-287; Knittel, T., Kessel, M., Kim, M.H., Gruss, P., 1995. A conserved enhancer of the human and murine Hoxa-7 gene specifies the anterior boundary of expression during embryonal development. Development 121, 1077-1088). We also show that chick Hoxa-7 and a-10 expression domains spread forward into regions of somites that are initially negative for the expression of these genes. We discuss this as evidence that Hox expression in paraxial mesoderm spreads forward, as earlier found for neurectoderm and lateral plate mesoderm, in a process that occurs independently of cell movement.
在进化过程中，解剖结构沿前后轴的转位一直是改变身体比例的常用机制。早期研究（Gaunt, S.J., 1994. 形态进化过程中Hox编码的保守性。《国际发育生物学杂志》38, 549 - 552；Burke, A.C., Nelson, C.E., Morgan, B.A., Tabin, C., 1995. Hox基因与脊椎动物轴向形态的进化。《发育》121, 333 - 346）表明中胚层衍生物（椎骨）的转位如何可归因于沿体节轴向系列的Hox基因表达的转位。我们现在展示脊髓神经节段排列的转位也如何与Hox基因表达域的变化相关。具体而言，我们展示了脊髓神经节中Hoxa - 7、a - 9和a - 10的表达域在小鼠和鸡中如何与臂丛神经和腰骶丛神经的位置相似对应，并且即便鸡的臂丛神经相对于小鼠向后移位了七个节段单位，情况依然如此。尽管Hoxa - 7表达边界存在这些显著的物种差异，但鸡Hoxa - 7基因上游多达5 kb处的顺式调控元件与小鼠中描述的元件在功能和结构上有很大的保守性（Puschel, A.W., Balling, R., Gruss, P., 1991. 不同元件导致谱系限制并确定Hox - 1.1表达的边界。《发育》112, 279 - 287；Knittel, T., Kessel, M., Kim, M.H., Gruss, P., 1995. 人和小鼠Hoxa - 7基因的一个保守增强子在胚胎发育过程中确定表达的前边界。《发育》121, 1077 - 1088）。我们还表明鸡Hoxa - 7和a - 10的表达域向前扩展到最初这些基因表达呈阴性的体节区域。我们将此作为证据进行讨论，即轴旁中胚层中的Hox表达向前扩展，如同先前在神经外胚层和侧板中胚层中发现的那样，是一个独立于细胞运动发生的过程。
