Oliver G, De Robertis E M, Wolpert L, Tickle C
Department of Biological Chemistry, University of California, Los Angeles 90024-1737.
EMBO J. 1990 Oct;9(10):3093-9. doi: 10.1002/j.1460-2075.1990.tb07506.x.
Homeobox gene XlHbox 1 is expressed in a mesodermal gradient in vertebrate forelimbs with maximal expression anteriorly and proximally and may encode positional values. In chick wing buds, anterior cells can be reprogrammed to form posterior structures by grafts of polarizing region tissue and by beads soaked in retinoic acid (RA), which is a good candidate for an endogenous morphogen. Applications of RA anteriorly or at the bud apex, treatments which produce duplicated digits or truncations respectively, substantially increase the extent of mesodermal XlHbox 1 expression. Polarizing region grafts that also produce additional digits lead to a moderate increase. The effects of RA application and the behaviour of transplanted tissue show that only anterior cells are competent to express XlHbox 1 and that expression is cell autonomous. Ectodermal expression in wing buds is enhanced by RA but not by polarizing region grafts and ectoderm/mesoderm recombinations show that the mesoderm is irreversibly affected. The changes in mesodermal expression do not fit the predictions of the simple model that XlHbox 1 encodes anterior positional values but are correlated with a series of novel malformations of the shoulder girdle which, in normal wing buds, is derived from cells expressing XlHbox 1.
同源框基因XlHbox 1在脊椎动物前肢中以中胚层梯度表达，在前部和近端表达量最高，可能编码位置值。在鸡胚翅芽中，通过极化区域组织移植和浸泡在视黄酸（RA）中的珠子，前部细胞可被重新编程形成后部结构，视黄酸是内源性形态发生素的良好候选者。在前部或翅芽顶端应用视黄酸，分别产生重复指或截断的处理，可显著增加中胚层XlHbox 1的表达范围。同样产生额外指的极化区域移植导致适度增加。视黄酸应用的效果和移植组织的行为表明，只有前部细胞能够表达XlHbox 1，且表达是细胞自主的。翅芽中的外胚层表达通过视黄酸增强，但极化区域移植不能增强，外胚层/中胚层重组表明中胚层受到不可逆影响。中胚层表达的变化不符合XlHbox 1编码前部位置值的简单模型的预测，但与一系列新颖的肩带畸形相关，在正常翅芽中，肩带由表达XlHbox 1的细胞衍生而来。
