Alibardi Lorenzo
Dipartimento di Biologia evoluzionistica sperimentale, University of Bologna, Via Selmi 3, 40126, Bologna, Italy.
Anat Sci Int. 2009 Sep;84(3):189-99. doi: 10.1007/s12565-009-0015-4. Epub 2009 Mar 4.
The histogenesis and cornification of claws in zebrafinch embryos has been analyzed. At 10-12 days post-deposition, the epidermis at the tip of the toes forms placode-like anlage associated with a mesenchymal condensation and with a terminal phalange. Claws seem to be modified scales, the dorsal side of which becomes the unguis whereas a ventral scale is the origin of the sub-unguis. At 14-15 days, numerous keratinocytes form the unguis, the corneous layer of which becomes thicker than in the sub-unguis and accumulates beta-keratin and lipids. Keratin bundles are mainly directed toward the tip of the claw and have a prevalent parallel orientation. Unguis corneocytes are thicker and accumulate more beta-keratin than corneocytes of the sub-unguis. Mature corneocytes become partially fused in a compact corneous layer at 17-18 days, near hatching. During growth of the unguis, the embryonic epidermis and beta-keratin cells curve over the tip of the claw and localize in the ventral part of the claw, forming the claw pad. The latter is shed at hatching leaving the pointed claw made of harder corneous layers in the unguis side of the claw.
对斑马雀胚胎爪的组织发生和角质化进行了分析。在产卵后10 - 12天，脚趾尖端的表皮形成与间充质凝聚和末节指骨相关的基板样原基。爪似乎是经过修饰的鳞片，其背侧成为爪甲，而腹侧鳞片是爪下皮的起源。在14 - 15天，大量角质形成细胞形成爪甲，其角质层比爪下皮的角质层更厚，并积累β - 角蛋白和脂质。角蛋白束主要指向爪的尖端，且普遍呈平行排列。爪甲角质形成细胞比爪下皮的角质形成细胞更厚，积累的β - 角蛋白更多。在接近孵化的17 - 18天，成熟的角质形成细胞在致密的角质层中部分融合。在爪甲生长过程中，胚胎表皮和β - 角蛋白细胞在爪的尖端弯曲并定位在爪的腹侧部分，形成爪垫。后者在孵化时脱落，在爪的爪甲侧留下由更硬的角质层构成的尖爪。
