Shankland M, Weisblat D A
Dev Biol. 1984 Dec;106(2):326-42. doi: 10.1016/0012-1606(84)90231-8.
The o and p bandlets of the leech embryo are parallel columns of ectodermal blast cells which are identified by their relative positions, and which during normal embryogenesis follow distinct developmental pathways. A previous study showed that o blast cells are initially capable of following either the O or P pathway, and suggested that commitment to the O pathway depends upon interaction with the adjacent p bandlet. To better understand the nature and timing of this interaction we examined the fate of o blast cells whose p blast cell neighbors had been selectively ablated by photoexcitation of a fluorescent lineage tracer. If an o blast cell has not yet begun its secondary divisions, its normal commitment to the O pathway can be effectively prevented by ablation of the adjacent p bandlet. Comparing the outcome of progressively later lesions reveals that the progeny of the o blast cell become committed to the O pathway in a series of three discrete steps, and that these steps occur around the time of the first three blast cell divisions. Each of the three events affects a different subset of elements within the blast cell clone, and apparently commits those elements to either the O or P pathway depending upon the presence or absence of the other bandlet. These changes in blast cell fate are coextensive with the lesion along the bandlet's length, suggesting that the interaction of the two bandlets is localized to neighboring cells.
水蛭胚胎的o和p带区是外胚层胚细胞的平行列，可通过它们的相对位置来识别，并且在正常胚胎发生过程中遵循不同的发育途径。先前的一项研究表明，o胚细胞最初能够遵循O或P途径，并表明对O途径的定向分化取决于与相邻p带区的相互作用。为了更好地理解这种相互作用的性质和时间，我们研究了其p胚细胞邻居已通过荧光谱系示踪剂的光激发被选择性切除的o胚细胞的命运。如果一个o胚细胞尚未开始其二次分裂，那么通过切除相邻的p带区可以有效地阻止其对O途径的正常定向分化。比较逐渐延迟的损伤结果表明，o胚细胞的后代通过三个离散步骤的序列定向分化到O途径，并且这些步骤发生在最初的三次胚细胞分裂时期左右。这三个事件中的每一个都会影响胚细胞克隆内不同的元素子集，并且显然根据另一个带区的存在或不存在将这些元素定向到O或P途径。胚细胞命运的这些变化与沿着带区长度的损伤范围相同，表明两个带区的相互作用局限于相邻细胞。
