Dane P J, Tucker J B
J Embryol Exp Morphol. 1985 Jun;87:145-61.
Distinct changes in epidermal cell shaping largely define the overall pattern of growth and form during generation of the ectodermal ridge and early stages of fin fold morphogenesis. The epidermal portion of the ridge and early fin fold are formed from a strip of epidermal cells that is only six to nine cells wide. There is apparently no increase in the number of these cells during initial formation of the ridge and its subsequent conversion into a fin fold which contains extracellular matrix fibres. Epidermal cells adopt a wedge-shaped morphology during ridge production. Distinct changes in the shaping and contact relationships between basal portions of these cells generate intercellular spaces at several discrete loci within the ridge. These spaces become continuous with each other to form a subepidermal space. Hence, the subepidermal space is not produced by straight-forward folding of an epidermal sheet. Cells flanking the sides of the ridge start to flatten as it is converted into a fin fold. A continuous row of distinctive cells is positioned along the apex of the developing fold. The term 'cleft cells' is suggested for these apical cells. Each cleft cell retains a wedge-shaped form during fold formation and develops a basal cleft-shaped invagination. Invaginations are aligned in neighbouring cleft cells so that these cells cap the distal boundary of the subepidermal space where collagenous extracellular fibres called actinotrichia run anteroposteriorly along the length of the fin fold. This orientation is in direct contrast to the proximodistal orientation of actinotrichia within the remainder of the subepidermal space. During early stages of fold production a temporary set of previously unreported extracellular cross fibres spans the subepidermal space at right angles to actinotrichia. These configurations of extracellular fibres could be advantageous for maintaining the structural integrity of the early fin fold.
表皮细胞形态的明显变化在很大程度上决定了外胚层嵴形成和鳍褶形态发生早期阶段的整体生长模式和形态。嵴和早期鳍褶的表皮部分由一条仅六到九个细胞宽的表皮细胞带形成。在嵴的初始形成及其随后转化为含有细胞外基质纤维的鳍褶过程中，这些细胞的数量显然没有增加。在嵴的产生过程中，表皮细胞呈现出楔形形态。这些细胞基部之间的形态和接触关系的明显变化在嵴内的几个离散位点产生细胞间空间。这些空间相互连通形成一个皮下空间。因此，皮下空间不是由表皮片的直接折叠产生的。当嵴转化为鳍褶时，其两侧的细胞开始变平。沿着发育中的褶皱顶端排列着一排连续的独特细胞。建议将这些顶端细胞称为“裂隙细胞”。每个裂隙细胞在褶皱形成过程中保持楔形形态，并形成一个基部裂隙状内陷。相邻裂隙细胞中的内陷排列对齐，使得这些细胞覆盖皮下空间的远端边界，在该边界处，称为肌动蛋白丝的胶原细胞外纤维沿着鳍褶的长度前后延伸。这种方向与皮下空间其余部分中肌动蛋白丝的近端到远端方向形成直接对比。在褶皱产生的早期阶段，一组暂时的、以前未报道过的细胞外交叉纤维以与肌动蛋白丝成直角的方式横跨皮下空间。这些细胞外纤维的构型可能有利于维持早期鳍褶的结构完整性。
