Leber S M, Breedlove S M, Sanes J R
Department of Anatomy and Neurobiology, Washington University School of Medicine, St. Louis, Missouri 63110.
J Neurosci. 1990 Jul;10(7):2451-62. doi: 10.1523/JNEUROSCI.10-07-02451.1990.
We have used recombinant retroviruses as lineage markers to study the genealogy of motoneurons (MNs) in the chick spinal cord. We infected individual progenitors by injecting virions into the neural tube at stages 11-18, a few cell divisions before MNs are born. The descendants of infected cells were subsequently detected with a histochemical stain for beta-galactosidase (lacZ), the product of the retrovirally introduced gene. Clonally related, lacZ-positive cells formed clusters that were usually radial or planar in shape. The cells that comprised these clones were classified by morphology, size, and location. About 15% of the clones in the spinal cord contained MNs, and these were studied further. Multicellular clones that contained only MNs were infrequent. Instead, close relatives of MNs included a variety of other neurons, as well as glia and ependymal cells. Most non-MNs in these clones were found in the ventral and intermediate parts of the spinal cord. Neurons included interneurons and autonomic preganglionic neurons in the column of Terni. Labeled glia were found in both the gray and white matter and included astrocytes and cells tentatively identified as oligodendrocytes. Thus, even shortly before MNs are born, their progenitors are multipotential. Clonally related MNs were not restricted to a single motor pool. Some clones contained MNs in both the medial and lateral parts of the lateral motor column, which are known to innervate distinct groups of limb muscles. Furthermore, some clones contained MNs in the medial motor column (which innervate axial muscles) as well as in the lateral motor column. In contrast, the dispersal of clonally related MNs (and other neurons) was restricted in the rostrocaudal axis; most clones were less than one-quarter segment in length. Thus, MNs derived from a single progenitor are more likely to share rostrocaudal position than synaptic targets. To investigate the fate of clonally related MNs, we counted the number of MNs per clone at times before, during, and after the major period of MN death. The number of MNs per clone declined in precise parallel with the total number of MNs during this period, suggesting that neurons are eliminated without regard to their clone of origin. This result implies that the decision to live or die occurs on a cell-by-cell rather than a clone-by-clone basis.
我们利用重组逆转录病毒作为谱系标记，来研究鸡脊髓中运动神经元（MNs）的谱系。我们在第11 - 18阶段将病毒粒子注入神经管，在运动神经元诞生前进行几次细胞分裂，从而感染单个祖细胞。随后用组织化学方法对逆转录病毒导入基因的产物β - 半乳糖苷酶（lacZ）进行染色，检测被感染细胞的后代。克隆相关的、lacZ阳性细胞形成通常呈放射状或平面状的细胞簇。根据形态、大小和位置对构成这些克隆的细胞进行分类。脊髓中约15%的克隆包含运动神经元，并对其进行了进一步研究。仅包含运动神经元的多细胞克隆很少见。相反，运动神经元的近亲包括多种其他神经元，以及神经胶质细胞和室管膜细胞。这些克隆中的大多数非运动神经元位于脊髓的腹侧和中间部分。神经元包括中间神经元和特尼柱中的自主神经节前神经元。在灰质和白质中均发现有标记的神经胶质细胞，包括星形胶质细胞和初步鉴定为少突胶质细胞的细胞。因此，即使在运动神经元诞生前不久，它们的祖细胞也是多能的。克隆相关的运动神经元并不局限于单个运动池。一些克隆在外侧运动柱的内侧和外侧部分均包含运动神经元，已知这两部分支配不同组的肢体肌肉。此外，一些克隆在内侧运动柱（支配轴肌）以及外侧运动柱中均包含运动神经元。相比之下，克隆相关的运动神经元（以及其他神经元）在前后轴上的分散受到限制；大多数克隆的长度小于四分之一个节段。因此，源自单个祖细胞的运动神经元比其突触靶点更有可能共享前后位置。为了研究克隆相关运动神经元的命运，我们在运动神经元死亡的主要时期之前、期间和之后，对每个克隆中的运动神经元数量进行了计数。在此期间，每个克隆中的运动神经元数量与运动神经元总数精确平行下降，这表明神经元的消除与它们的起源克隆无关。这一结果意味着生死抉择是在逐个细胞而非逐个克隆的基础上发生的。
