Christ B, Jacob H J, Jacob M, Brand B
Department of Developmental Biology, Ruhr-University Bochum.
Acta Morphol Neerl Scand. 1986;24(4):249-68.
Human hand anlagen of different developmental stages are studied light and scanning electron microscopically. The findings are compared with experimental and ultrastructural results obtained from avian limb anlagen. Shaping, cell differentiation and the spatial arrangement of different cells are found to be the basic processes of hand development. The shaping of the arm and hand seems to anticipate future grasping movements. Factors controlling this developmental process are on the one hand the apical ectodermal ridge (AER) that maintains in the underlying mesoderm a high level of mitotic activity, and on the other hand a species-specific pattern of cell death in different zones of arm and hand. Interdigital cell death, microfilament bundles included in the basal compartment of AER cells, and local anchorings of the AER ectoderm by collagen fibrils are involved in finger separation. The flexion creases are genetically fixed and their development cannot be explained by mechanical factors. It is found that the early hand anlage is already composed of relatively autonomous founder cells committed to different lineages. This is true for the muscle precursor cells which originate from the brachial somites. These migrating somite cells are determined to belong to the myogenic lineage. However, their distribution, mitotic activity and later arrangement in single muscles are controlled by factors localized within the hand itself. Tendons develop autonomously from somatopleural cells. Other already committed cells are the angioblasts forming the endothelial lining of the blood vessels, the neural crest cells differentiating into melanocytes and Schwann cells, and the blood-derived cells like chrondro- or osteoclasts. The differentiation of somatopleural cells into cartilage, connective tissue or smooth muscle depends on their position within the hand anlage. Possible mechanisms leading to the specific pattern are discussed.
对不同发育阶段的人类手部原基进行了光镜和扫描电镜研究。将这些发现与从禽类肢体原基获得的实验和超微结构结果进行了比较。发现塑形、细胞分化以及不同细胞的空间排列是手部发育的基本过程。手臂和手部的塑形似乎预示着未来的抓握动作。控制这一发育过程的因素一方面是顶端外胚层嵴（AER），它在其下方的中胚层维持高水平的有丝分裂活性，另一方面是手臂和手部不同区域中物种特异性的细胞死亡模式。指间细胞死亡、AER细胞基底区包含的微丝束以及AER外胚层通过胶原纤维的局部锚定参与手指分离。屈褶是由基因决定的，其发育不能用机械因素来解释。发现早期手部原基已经由致力于不同谱系的相对自主的奠基细胞组成。源自臂部体节的肌肉前体细胞就是如此。这些迁移的体节细胞被确定属于肌源性谱系。然而，它们在单个肌肉中的分布、有丝分裂活性和后期排列受手部自身局部因素的控制。肌腱从体壁细胞自主发育。其他已经定向的细胞有成血管细胞，形成血管的内皮衬里；神经嵴细胞分化为黑素细胞和施万细胞；以及血液来源的细胞，如软骨细胞或破骨细胞。体壁细胞向软骨、结缔组织或平滑肌的分化取决于它们在手部原基中的位置。讨论了导致特定模式的可能机制。
