Analysis of the mechanisms of cell death that involves a specific subgroup of motoneurons.

为了确定垂死的运动神经元（MN）经历程序性细胞死亡（PCD）在相对较早的阶段（E4-E5在鸡胚），只有在非肢体支配颈脊髓的身份，我们检查了亚组特异性MN标记物（Isl 1，Is 12，Lim 3，MNR 2和Foxpl）的表达在垂死的MN。PCD仅发生在表达Isl 1、Isl 2、MNR 2和FoxP 1但缺乏Lim 3表达的MN亚组中。这个Lim 3阴性（Lim 3）MN亚组在失去Lim 3表达后，E4时在腹角背外侧区域出现一个独特的亚群，E5时不再观察到。然而，在通过Bcl 2过表达拯救MN后，Lim 3-至少持续到E5-5.5。当Lim 3在脊髓一侧过表达时，死亡MN的数量在E4.5时显著减少，并且在细胞死亡期（E5.5）后存活的健康MN的数量增加。这些结果表明，Lim 3的下调参与了早期死亡的宫颈MN的细胞死亡命运的规范。此外，Foxpl由垂死的MN表达的事实表明，对宫颈段特异的Hox蛋白可能在这种类型的细胞死亡中起作用。Hox基因的原位杂交显示Hoxc 5、Hoxa 3、Hoxa 5在颈段运动神经元表达，其表达范围覆盖了运动神经元早期死亡的节段。这些Hox基因可能参与决定运动神经元亚群的细胞死亡。

To determine the identity of the dying motoneurons (MNs) undergoing programmed cell death (PCD) at relatively early stages (E4-E5 in the chick embryo) and only in the non-limb innervating cervical spinal cord, we examined expression of subgroup-specific MN markers (Isl1, Is12, Lim3, MNR2 and Foxpl) in the dying MNs. PCD occurs only in a subgroup of MNs that express Isl1, Isl2, MNR2 and FoxPl but that lack Lim3 expression. This Lim3-negative (Lim3) MN subgroup appears as a distinct subpopulation in the dorsolateral region of the ventral horn by E4 after losing Lim3 expression and they are no longer observed by E5. However, following the rescue of MNs by Bc12 overexpression, Lim3- persisted at least until E5-5.5. When Lim3 was overexpressed on one side of the spinal cord, the number of dying MNs was markedly decreased at E4.5 and the number of surviving healthy MNs was increased after the period of cell death (E5.5). These results suggest that the downregulation of Lim3 is involved in the specification of the cell death fate of early dying cervical MNs. Furthermore, the fact that Foxpl is expressed by dying MNs suggests that Hox proteins that are specific to the cervical segments may play a role in this type of cell death. In situ hybridizaiton for Hox genes revealed that Hoxc5, Hoxa3, Hoxa5 are expressed by cervical motoneurons and their rostro-caudal extents of expression cover the segments where early motoneuron death occurs. These Hox genes might be involved in the determination of motoneuron subgroups that under go cell death.