Streck R D, Wood T L, Hsu M S, Pintar J E
Department of Anatomy and Cell Biology, Columbia University College of Physicians and Surgeons, New York 10032.
Dev Biol. 1992 Jun;151(2):586-96. doi: 10.1016/0012-1606(92)90196-n.
Since the rapid proliferation of cells in a directed manner is a necessary component of limb formation, the distribution of locally produced mitogenic molecules within the developing limb is of considerable interest. We have used in situ hybridization to localize transcripts for both insulin-like growth factor binding protein-2 (IGFBP-2) and its ligands, the insulin-like growth factors I and II (IGF-I and IGF-II), within limb buds of rat embryos 10-16 days after conception (equivalent to stages 1-12 of mouse limb morphogenesis, Wanek et al, 1989. J. Exp. Zool. 249, 41-49). The mRNA for IGFBP-2 is very abundant in an anterior-posterior strip of ectoderm along the distal edge of the limb bud (the progenitor of the apical ectodermal ridge or AER) from as early as limb stage 1 (Embryonic Day 10) and is much less abundant in the rest of the limb ectoderm. A high level of IGFBP-2 expression continues to characterize the AER following its definitive appearance (stage 3) and throughout its existence (until stage 7). This is a period of rapid outgrowth during which the rate of mesodermal cell division is highest in cells nearest to the AER. The AER is known to have mitogenic activity in vitro and to direct limb outgrowth in vivo, but, until recently, few putative molecular correlates of these activities have been detected. The transcripts for IGF-I and IGF-II are also present at high abundance in developing limbs, especially in mesodermally derived cells. IGF-I mRNA is abundant in presumptive limb mesoderm from the beginning of limb outgrowth (just before stage 1), but is very low or undetectable in much of the rest of the embryo, while IGF-II mRNA becomes very abundant in limb mesoderm at stage 2. The distribution in limbs of both IGF-I and IGF-II mRNA changes dramatically during outgrowth and differentiation, so that their expression characterizes complementary populations of cells by stage 11. Taken together, these data suggest that IGFs and the IGF binding proteins, which may modulate IGF action, contribute to limb outgrowth and patterning.
由于细胞以定向方式快速增殖是肢体形成的必要组成部分，因此发育中的肢体中局部产生的促有丝分裂分子的分布备受关注。我们利用原位杂交技术，在受孕后10 - 16天的大鼠胚胎肢体芽中定位胰岛素样生长因子结合蛋白-2（IGFBP-2）及其配体胰岛素样生长因子I和II（IGF-I和IGF-II）的转录本（相当于小鼠肢体形态发生的第1 - 12阶段，Wanek等人，1989年。《实验动物学杂志》249卷，41 - 49页）。早在肢体发育第1阶段（胚胎第10天），IGFBP-2的mRNA就在沿着肢体芽远端边缘的前后条带外胚层（顶端外胚层嵴或AER的祖细胞）中非常丰富，而在肢体其余外胚层中则少得多。在AER最终出现（第3阶段）后及其整个存在期间（直到第7阶段），高水平的IGFBP-2表达一直是其特征。这是一个快速生长的时期，在此期间，中胚层细胞分裂速率在最靠近AER的细胞中最高。已知AER在体外具有促有丝分裂活性，并在体内指导肢体生长，但直到最近，很少检测到这些活性的假定分子相关物。IGF-I和IGF-II的转录本在发育中的肢体中也大量存在，尤其是在中胚层来源的细胞中。IGF-I mRNA从肢体开始生长（就在第1阶段之前）时就在假定的肢体中胚层中丰富，但在胚胎其余大部分区域中非常低或无法检测到，而IGF-II mRNA在第2阶段时在肢体中胚层中变得非常丰富。在生长和分化过程中，IGF-I和IGF-II mRNA在肢体中的分布发生了巨大变化，因此到第11阶段时，它们的表达表征了互补的细胞群体。综上所述，这些数据表明，可能调节IGF作用的IGF和IGF结合蛋白有助于肢体生长和模式形成。
