Niederreither K, Ward S J, Dollé P, Chambon P
Institute de Génétique et de Biologie Moléculaire et Cellulaire, CNRS/INSERM/ULP/Collége de France, Strasbourg.
Dev Biol. 1996 Jun 15;176(2):185-98. doi: 10.1006/dbio.1996.0126.
This study reports a morphological, skeletal, and molecular characterization of the supernumerary limbs induced by systemic administration of all-trans retinoic acid to egg-cylinder stage mouse embryos. As initially described by Rutledge et al. (Proc. Natl. Acad. Sci. USA 91, 5436, 1994), we have found that oral administration of all-trans retinoic acid (70 mg/kg body weight) at 5.5 days postcoitum induced the formation of supernumerary limbs. Most often, these arose as a pair of extra buds located caudally and ventrally to the normal (orthotopic) hindlimb buds without duplication of the lower body axis. The resulting one or two supernumerary hindlimbs were connected to an imperfectly mirror-image-duplicated pelvic girdle. Variable truncations of the stylopodium and zeugopodium skeleton, as well as abnormal splitting of the distal skeleton, were frequently observed. The apical ectodermal ridge of the extra limb buds expressed expected growth factor genes. However, an ectopic anterior expression of Sonic hedgehog and Hoxd-13 was seen in the supernumerary buds, suggesting that these buds would incorporate potential polarizing cells of the hindlimb or genital field and generate an ectopic polarizing zone. This is consistent with the reverse orientation of most supernumerary limbs at later stages. Some of the buds did not express limb-specific markers and were thus expected to degenerate or form nonlimb structures, as observed in an adult specimen. Less frequently, extra limb buds with normal polarity were associated to a duplicated lower body axis. Retinoic acid also generated a novel type of duplication in which "twin" hindlimbs with two parallel apical ectodermal ridges and zones of polarizing activity arose on one side of the embryo.
本研究报告了对全反式维甲酸全身给药至卵柱期小鼠胚胎所诱导的多余肢体进行的形态学、骨骼学和分子特征分析。如Rutledge等人最初所描述的（《美国国家科学院院刊》91, 5436, 1994），我们发现，在交配后5.5天口服全反式维甲酸（70毫克/千克体重）可诱导多余肢体的形成。这些多余肢体最常见的是作为一对额外的芽出现，位于正常（原位）后肢芽的尾侧和腹侧，且没有下体轴的重复。由此产生的一或两个多余后肢与一个不完全镜像重复的骨盆带相连。经常观察到肱骨和桡尺骨骨骼的可变截断，以及远端骨骼的异常分裂。额外肢体芽的顶端外胚层嵴表达了预期的生长因子基因。然而，在多余芽中观察到音猬因子和Hoxd - 13的异位前部表达，这表明这些芽会纳入后肢或生殖区域的潜在极化细胞并产生异位极化区。这与大多数多余肢体在后期的反向定向是一致的。一些芽不表达肢体特异性标记，因此预计会退化或形成非肢体结构，如在一个成年标本中所观察到的。较少见的情况是，具有正常极性的额外肢体芽与重复的下体轴相关联。维甲酸还产生了一种新型的重复，其中在胚胎的一侧出现了带有两个平行顶端外胚层嵴和极化活性区的“孪生”后肢。
