Fromental-Ramain C, Warot X, Lakkaraju S, Favier B, Haack H, Birling C, Dierich A, Doll e P, Chambon P
Institut de Génétique et de Biologie Moléculaire et Cellulaire, CNRS/INSERM/ULP, Collège de France, Strasbourg.
Development. 1996 Feb;122(2):461-72. doi: 10.1242/dev.122.2.461.
Using gene targeting, we have produced mice with a disruption of Hoxa-9 or Hoxd-9, two paralogous Abdominal B-related genes. During embryogenesis, these genes are expressed in limb buds and along the vertebral axis with anterior expression boundaries at the level of prevertebra #20 for Hoxa-9 and #23 for Hoxd-9. Skeletal analysis revealed homeotic transformations corresponding to anteriorisations of vertebrae #21 to #25 (L1 to L5) in the lumbar region of Hoxa-9-/- mutants; vertebrae #23 to #25 (L3 to L5) in the lumbar region together with vertebrae #28, #30 and #31 (S2, S4 and Ca1) in the sacrum and tail were anteriorized in Hoxd-9-/- mutants. Thus, anteriorisation of vertebrae #23 to #25 were common to both phenotypes. Subtle forelimb (but not hindlimb) defects, corresponding to a reduction of the humerus length and malformation of its deltoid crest, were also observed in Hoxd-9-/-, but not in Hoxa-9-/-, mutant mice. By intercrosses between these two lines of mutant mice, we have produced Hoxa-9/Hoxd-9 double mutants which exhibit synergistic limb and axial malformations consisting of: (i) an increase of penetrance and expressivity of abnormalities present in the single mutants, and (ii) novel limb alterations at the level of the forelimb stylopod and additional axial skeleton transformations. These observations demonstrate that the two paralogous genes Hoxa-9 and Hoxd-9 have both specific and redundant functions in lumbosacral axial skeleton patterning and in limb morphogenesis at the stylopodal level. Taken all together, the present and previously reported results show that disruption of different Hox genes can produce similar vertebral transformations, thus supporting a combinatorial code model for specification of vertebral identity by Hox genes.
利用基因打靶技术，我们培育出了Hoxa - 9或Hoxd - 9基因被破坏的小鼠，这两个基因是同源的与腹部B相关的基因。在胚胎发育过程中，这些基因在肢芽和沿脊椎轴表达，Hoxa - 9的前表达边界在第20节椎骨水平，Hoxd - 9的前表达边界在第23节椎骨水平。骨骼分析显示，Hoxa - 9基因敲除突变体腰椎区域第21至25节椎骨（L1至L5）出现了对应于椎体向前转化的同源异型转化；Hoxd - 9基因敲除突变体中，腰椎区域的第23至25节椎骨（L3至L5）以及骶骨和尾部的第28、30和31节椎骨（S2、S4和Ca1）向前转化。因此，第23至25节椎骨的向前转化是两种表型共有的特征。在Hoxd - 9基因敲除突变体小鼠中还观察到了细微的前肢（而非后肢）缺陷，表现为肱骨长度缩短及其三角嵴畸形，而在Hoxa - 9基因敲除突变体小鼠中未观察到这种情况。通过这两种突变小鼠品系的杂交，我们培育出了Hoxa - 9/Hoxd - 9双突变体，其表现出协同的肢体和轴向畸形，包括：（i）单突变体中出现的异常的外显率和表达度增加，以及（ii）在前肢肢干水平出现新的肢体改变和额外的轴向骨骼转化。这些观察结果表明，两个同源基因Hoxa - 9和Hoxd - 9在腰骶部轴向骨骼模式形成和肢干水平的肢体形态发生中具有特定和冗余的功能。综合来看，目前和先前报道的结果表明，不同Hox基因的破坏可产生相似的椎体转化，从而支持了Hox基因指定椎体身份的组合密码模型。
