Schnabel R
Max-Planck-Institut für Biochemie, Martinsried, Germany.
Development. 1995 Jul;121(7):2219-32. doi: 10.1242/dev.121.7.2219.
During the first four cleavage rounds of the Caenorhabditis elegans embryo, five somatic founder cells AB, MS, E, C and D are born, which later form the tissues of the embryo. The classical criterion for a cell-autonomous specification of a tissue is the capability of primordial cells to produce this tissue in isolation from the remainder of the embryo. By this criterion, the somatic founder cells MS, C and D develop cell-autonomously. Laser ablation experiments, however, reveal that within the embryonic context these blastomeres form a network of duelling cellular interactions. During normal development, the blastomere D inhibits muscle specification in the MS and the C lineage inhibits muscle specification in the D lineage. These inhibitory interactions are counteracted by two activating inductions. As described before the inhibition of body wall muscle in MS is counteracted by an activating signal from the ABa lineage. Body wall muscle in the D lineage is induced by MS descendants, which suppress an inhibitory activity of the C lineage. The interaction between the D and the MS lineage occurs through the C lineage. An interesting feature of these cell-cell interactions is that they do not serve to discriminate between equivalent cells but are permissive or nonpermissive inductions. No evidence was found that the C-derived body wall muscle also depends on an induction, which suggests that possibly three different pathways coexist in the early embryo to specify body wall muscle, two of which are, in different ways, influenced by cell-cell interactions and a third that is autonomous. This work supplies evidence that cells may acquire transient states during embryogenesis that influence the specification of other cells in the embryo. These states, however, may not be reflected in the developmental potentials of the cells themselves. They can only be scored indirectly by their action on the specification of other cells in the embryo. Blastomeres that behave cell-autonomously in isolation are nevertheless subjected to cell-cell interactions in the embryonic context. Why this should be is an intriguing question. The classical notion has been that blastomeres are specified autonomously in nematodes. In recent years, it was established that at least five inductions are required to determine the AB descendants of C. elegans, whereas the P1 descendants have been typically viewed to develop more autonomously. It appears now that inductions also play a major role during the determination of P1-derived blastomeres.
在秀丽隐杆线虫胚胎的前四轮卵裂过程中，产生了五个体细胞奠基细胞AB、MS、E、C和D，它们随后形成胚胎的组织。组织细胞自主特化的经典标准是原始细胞在与胚胎其余部分分离的情况下产生该组织的能力。根据这一标准，体细胞奠基细胞MS、C和D进行细胞自主发育。然而，激光消融实验表明，在胚胎环境中，这些卵裂球形成了一个相互竞争的细胞间相互作用网络。在正常发育过程中，卵裂球D抑制MS中的肌肉特化，而C谱系抑制D谱系中的肌肉特化。这些抑制性相互作用被两种激活诱导所抵消。如前所述，MS中体壁肌肉的抑制被来自ABa谱系的激活信号所抵消。D谱系中的体壁肌肉由MS后代诱导，MS后代抑制C谱系的抑制活性。D和MS谱系之间的相互作用通过C谱系发生。这些细胞间相互作用的一个有趣特征是，它们不是用于区分等同细胞，而是允许性或非允许性诱导。没有发现证据表明C衍生的体壁肌肉也依赖于诱导，这表明早期胚胎中可能存在三种不同的途径来特化体壁肌肉，其中两种以不同方式受到细胞间相互作用的影响，第三种是自主的。这项工作提供了证据，表明细胞在胚胎发生过程中可能获得影响胚胎中其他细胞特化的瞬时状态。然而，这些状态可能不会反映在细胞自身的发育潜能中。它们只能通过其对胚胎中其他细胞特化的作用来间接评分。在分离情况下表现为细胞自主行为的卵裂球在胚胎环境中仍会受到细胞间相互作用的影响。为什么会这样是一个有趣的问题。传统观念认为线虫中的卵裂球是自主特化的。近年来，已确定至少需要五次诱导来确定秀丽隐杆线虫的AB后代，而P1后代通常被认为发育得更自主。现在看来，诱导在P1衍生的卵裂球的确定过程中也起着重要作用。
