Alibardi Lorenzo
Dipartimento di Biologia, University of Bologna, via Selmi 3, 40126 Bologna, Italy.
Ann Anat. 2006 Jul;188(4):303-18. doi: 10.1016/j.aanat.2006.01.011.
The present study deals with the cell structure and three-dimensional organization of barb and barbule cells within barb ridges of down feathers and juvenile feathers in the chick embryo. Juvenile feathers represent the second generation of feathers in the wing, and replace down feathers some weeks after hatching. Within the follicle of juvenile feathers, at 16-18 days of embryonic development, barb ridges are more numerous than in down feathers. Barb ridges of juvenile feathers contain more cells in their barbule and axial plates with respect to barb ridges of down feathers. This condition determines the formation of longer barbules inserted in the rami of juvenile feathers than barbules of down feathers. Barb ridges of juvenile feathers merge with the rachidial ridge so that pennaceous feathers are formed. Barbule cells are surrounded by cytoplasmic elongation from barb vane ridge cells located in the axial plate, which constitute most of the axial plate. The degeneration of supportive cells among barbule cells branching from barbs determine the formation of spaces between barbules. The study emphasizes that, in addition to the size of the dermal papilla, it is the length of barb ridges and the infiltration of barb ridge vane cells among barbule cells that determine the size and length of feathers. The knowledge of the cell structure of barb ridges allows understanding not only of how feathers develop but also gives insights into their evolution. Based on changes of the process of barb ridge morphogenesis some hypotheses on the evolution of plumulaceous and pennaceous feathers are presented. Feathers derived from the process of carving-out supportive cells within barb ridges and from the specific pattern of fusion of barb/barbule cells. This process initially produced variably branched down feathers and later, after barb ridge fusion, a rachis. From the modulation in the pattern of barb ridge formation various pennaceous feathers later evolved.
本研究探讨了鸡胚绒羽和幼羽羽枝嵴内羽枝和羽小枝细胞的细胞结构及三维组织。幼羽是翅膀上的第二代羽毛，在孵化几周后取代绒羽。在胚胎发育16 - 18天时，幼羽毛囊内的羽枝嵴比绒羽中的更多。相对于绒羽的羽枝嵴，幼羽的羽枝嵴在其羽小枝和轴板中含有更多细胞。这种情况决定了幼羽羽枝中插入的羽小枝比绒羽的羽小枝更长。幼羽的羽枝嵴与羽轴嵴融合，从而形成正羽。羽小枝细胞被位于轴板中的羽片嵴细胞的细胞质延伸所包围，这些细胞构成了轴板的大部分。从羽枝分支出来的羽小枝细胞之间的支持细胞退化，决定了羽小枝之间空间的形成。该研究强调，除了真皮乳头的大小外，决定羽毛大小和长度的是羽枝嵴的长度以及羽枝嵴羽片细胞在羽小枝细胞中的浸润情况。对羽枝嵴细胞结构的了解不仅有助于理解羽毛的发育过程，还能深入了解其进化过程。基于羽枝嵴形态发生过程的变化，提出了一些关于绒羽和正羽进化的假说。羽毛起源于羽枝嵴内支持细胞的剔除过程以及羽枝/羽小枝细胞的特定融合模式。这个过程最初产生了分支各异的绒羽，后来在羽枝嵴融合后产生了羽轴。随后，从羽枝嵴形成模式的调节中演化出了各种正羽。
