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

为了确定正在死亡的运动神经元(MN)在相对早期(鸡胚胎中的E4-E5)经历程序性细胞死亡(PCD)以及仅在非肢体支配的颈髓中的身份，我们检测了正在死亡的MN中亚群特异性MN标志物(Is11、Is12、Lim3、MNR2和Foxp1)的表达。PCD仅发生在表达Isl1、Isl2、MNR2和FoxP1但缺乏Lim3表达的MN的亚群中。这种Lim3阴性(Lim3)MN亚群在失去Lim3表达后，在E4出现在腹角背外侧区，E5不再观察到它们。然而，在BC12过表达挽救了MNS之后，Lim3-至少持续到E5-5.5。当LIM3在一侧脊髓过表达时，死亡的MN数量在E4.5时明显减少，而存活的健康MN的数量在细胞死亡后增加(E5.5)。这些结果提示，Lim3基因的下调参与了早期死亡宫颈MN细胞死亡命运的调控。此外，Foxp1在死亡的MN中表达的事实表明，针对宫颈节段的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在颈运动神经元表达，其表达的吻尾范围覆盖了发生早期运动神经元死亡的节段。这些HOX基因可能参与了GO细胞死亡下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.