Alibardi Lorenzo
Department of Evolutionary and Experimental Biology, University of Bologna, via Selmi 3, 40126 Bologna, Italy.
Anat Sci Int. 2009 Dec;84(4):269-79. doi: 10.1007/s12565-009-0033-2. Epub 2009 Apr 11.
During most of feather growth (anagen), the dermal papilla stimulates the collar epithelium to give rise to feather keratins accumulating cells that form most of the corneous material of barbs and the rachis. Aside from the induction of differentiated cells of the feather, the distal part of the papilla forms a loose connective tissue that nourishes the growing feather, termed the pulp. In the last stages of feather growth, the pulp undergoes a process of re-absorption and leaves empty cavities indicated as pulp cups surrounded by keratinized cells inside the calamus. The process of cornification of pulp cups in different species of birds has been described here by using electron microscopy and immunocytochemistry for keratins. Pulp cells accumulate bundles of soft (alpha)-keratin, but do not synthesise feather keratins as in the surrounding calamus cells. Cells of the pulp epithelium accumulate large amounts of lipids and form a softer keratinized epithelium surrounding the pulp. This type of keratinization resembles the formation of soft epidermis in apteric and interfollicular regions. The role of the cornified pulp epithelium is to limit water loss and to form a microbe barrier before the mature feather is moulted.
在大多数羽毛生长阶段（生长期），真皮乳头刺激领状上皮产生积累羽毛角蛋白的细胞，这些细胞构成了羽枝和羽轴的大部分角质物质。除了诱导羽毛的分化细胞外，乳头的远端形成一种疏松结缔组织，为生长中的羽毛提供营养，称为髓质。在羽毛生长的最后阶段，髓质经历重吸收过程，留下空泡，在羽根内表现为空的髓杯，周围被角质化细胞包围。本文利用电子显微镜和角蛋白免疫细胞化学技术描述了不同鸟类髓杯的角质化过程。髓质细胞积累柔软的（α）-角蛋白束，但不像周围羽根细胞那样合成羽毛角蛋白。髓质上皮细胞积累大量脂质，并形成围绕髓质的较软的角质化上皮。这种角质化类型类似于无羽区和毛囊间区域软表皮的形成。角质化髓质上皮的作用是在成熟羽毛换羽前限制水分流失并形成微生物屏障。
