Eyal-Giladi H, Khaner O
Department of Zoology, Hebrew University, Jerusalem, Israel.
Dev Biol. 1989 Jul;134(1):215-21. doi: 10.1016/0012-1606(89)90091-2.
When a posterior fragment of the chick's marginal zone (PM) was exchanged with equal sized lateral marginal zone fragment (LM), of the same blastoderm, its capacity to initiate an ectopic primitive streak (PS) was found to be both size and stage dependent. Good correlation was demonstrated between the areas of PM fragments and the number of cells they contained. In stage X blastoderms, PM fragments containing less than 1200 cells were incapable of initiating an ectopic PS. Transplanted PMs containing between 1200 and 1500 cells initiated a lateral ectopic PS in 50% of the cases, while in the other 50% a posterior PS developed from the original posterior side. PMs containing 1500 cells or more in all cases initiating an ectopic PS and inhibited the formation of a posterior PS. At stage XI, laterally transplanted PMs containing less than 1800 cells were not effective. Stage XI PMs containing 1800-2300 cells in some cases succeeded in initiating a lateral ectopic PS, in addition to the posterior one. Stage XI PMs containing 2300 cells or more invariably promoted the development of an ectopic PS, but were unable to suppress the formation of a posterior PS, so that two PSs developed in the same blastoderm, one posterior and one ectopic. When a stage XI PM fragment was laterally transplanted into a younger, stage X blastoderm, the minimal effective cell number needed to initiate an ectopic PS increased to at least 3000 cells, again without inhibiting the formation of a posterior PS. The inductive potential of a stage X PM is therefore at least twice that of a stage XI PM. The marginal zone belt of stage X blastoderms was checked for the decrease in its developmental potential from the posterior to the lateral side by evaluating its effect on the developmental expression of two competing stage X PMs, one located posteriorly and the other inserted laterally. The developmental expression of the laterally inserted PM was consistently inferior to that of the posterior PM. The developmental expression of each PM was not related to absolute size, but depended on the size ratio of lateral PM/posterior PM. When the ratio was 1.2 or less, only posterior PSs developed. When the ratio was 1.3-1.4, three different results were encountered: (1) only a posterior PS, (2) posterior plus lateral, and (3) only lateral PS. When the ratio was 1.5 or more, only a lateral PS developed, which suppressed the posterior PS.
当将鸡胚边缘区的后部片段（PM）与同一胚盘等大小的外侧边缘区片段（LM）进行交换时，发现其启动异位原条（PS）的能力既取决于大小也取决于阶段。PM片段的面积与其所含细胞数量之间显示出良好的相关性。在X期胚盘中，含有少于1200个细胞的PM片段无法启动异位PS。含有1200至1500个细胞的移植PM在50%的情况下启动外侧异位PS，而在另外50%的情况下，后位PS从原来的后侧发育形成。含有1500个或更多细胞的PM在所有情况下都启动异位PS并抑制后位PS的形成。在XI期，外侧移植的含有少于1800个细胞的PM无效。含有1800 - 2300个细胞的XI期PM在某些情况下除了后位PS外还成功启动了外侧异位PS。含有2300个或更多细胞的XI期PM总是促进异位PS的发育，但无法抑制后位PS的形成，从而在同一胚盘中形成两个PS，一个后位，一个异位。当将XI期PM片段外侧移植到较年轻的X期胚盘中时，启动异位PS所需的最小有效细胞数增加到至少3000个细胞，同样不会抑制后位PS的形成。因此，X期PM的诱导潜能至少是XI期PM的两倍。通过评估其对两个相互竞争的X期PM（一个位于后部，另一个插入外侧）发育表达的影响，检查了X期胚盘边缘区带从后部到外侧其发育潜能的降低情况。外侧插入的PM的发育表达始终低于后位PM。每个PM的发育表达与绝对大小无关，而是取决于外侧PM/后位PM的大小比例。当该比例为1.2或更低时，只形成后位PS。当比例为1.3 - 1.4时，会出现三种不同结果：（1）只形成后位PS，（2）后位加外侧PS，（3）只形成外侧PS。当比例为1.5或更高时，只形成外侧PS，其抑制了后位PS。
