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

为了确定在相对早期（鸡胚中的 E4-E5）且仅在非肢体神经支配的颈脊髓中经历程序性细胞死亡（PCD）的垂死运动神经元（MN）的身份，我们检查了垂死运动神经元中亚组特异性 MN 标记（Isl1、Is12、Lim3、MNR2 和 Foxpl）的表达。 PCD仅发生在表达Isl1、Isl2、MNR2和FoxPl但缺乏Lim3表达的MN亚组中。在失去 Lim3 表达后，这个 Lim3 阴性 (Lim3) MN 亚群在 E4 中作为一个独特的亚群出现在腹角的背外侧区域，并且在 E5 中不再观察到它们。然而，在通过 Bc12 过表达来拯救 MN 后，Lim3- 至少持续到 E5-5.5。当 Lim3 在脊髓一侧过度表达时，死亡 MN 的数量在 E4.5 时显着减少，而在细胞死亡期 (E5.5) 后，存活的健康 MN 的数量增加。这些结果表明 Lim3 的下调参与了早期死亡宫颈 MN 的细胞死亡命运的规范。此外，Foxp1 由垂死的 MN 表达的事实表明，颈段特异的 Hox 蛋白可能在这种类型的细胞死亡中发挥作用。 Hox基因的原位杂交显示Hoxc5、Hoxa3、Hoxa5由颈部运动神经元表达，并且它们的头尾表达范围覆盖了早期运动神经元死亡发生的节段。这些 Hox 基因可能参与细胞死亡的运动神经元亚群的确定。

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.