Canning D R, Amin T, Richard E
Department of Biological Sciences, Murray State University, Murray, Kentucky 42071-0009, USA.
Dev Dyn. 2000 Dec;219(4):545-59. doi: 10.1002/1097-0177(2000)9999:9999<::AID-DVDY1077>3.0.CO;2-3.
Avian gastrulation is dependent on the ingression of outer layer cells into the interior of the embryo by means of a transient structure referred to as the primitive streak. As the growing streak progresses through the central area pellucida of the blastoderm, selective de-epithelialization of epiblast cells results in the initial migratory cells of the primitive mesoderm and endoderm. Here, we have examined the possibility that extracellular matrix molecules of the epiblast basal lamina influence the selection of streak-specific epiblast cells. By using whole embryo culture, we have found that removal of chondroitin sulfate glycosaminoglycans at gastrulation stages leads to defective streak formation. In situ hybridization with streak-specific markers in these embryos reveals ectopic patterns of gene expression, suggesting that differentiation of primitive streak precursors in the pregastrula epiblast is independent of normal streak morphogenesis. In addition, in vitro assays with chondroitin sulfate containing matrices suggest that specific cells of the epiblast are inhibited from joining the streak during gastrulation. Taken together, these results indicate that the presence of chondroitin sulfate in the epiblast basal lamina facilitates the allocation of cells to the primary germ layers by preventing ectopic axis formation.
鸟类原肠胚形成依赖外层细胞通过一种称为原条的临时结构侵入胚胎内部。随着生长的原条穿过胚盘的中央透明区，上胚层细胞的选择性去上皮化产生了原始中胚层和内胚层的初始迁移细胞。在此，我们研究了上胚层基膜的细胞外基质分子影响原条特异性上胚层细胞选择的可能性。通过使用全胚胎培养，我们发现原肠胚形成阶段去除硫酸软骨素糖胺聚糖会导致原条形成缺陷。在这些胚胎中用原条特异性标记进行原位杂交揭示了基因表达的异位模式，表明原肠胚前期上胚层中原条前体的分化独立于正常的原条形态发生。此外，用含硫酸软骨素的基质进行的体外试验表明，上胚层的特定细胞在原肠胚形成过程中被抑制加入原条。综上所述，这些结果表明上胚层基膜中硫酸软骨素的存在通过防止异位轴形成促进细胞分配到初级胚层。
