Morphology of the developing down feathers of chick embryos. A descriptive study at the ultrastructural level of differentiation and keratinization.

TLDR: The morphology of the developing chick feather germ (down feather) was studied at the ultrastructural level from 8 to 18 days of incubation and the process of keratinization in the developing feather germ was described, discussed and compared to keratinisation in mammalian skin and hair as discussed by the authors.

Abstract: The morphology of the developing chick feather germ (down feather) was studied at the ultrastructural level from 8 to 18 days of incubation. The process of keratinization in the developing feather germ was described, discussed and compared to keratinization in mammalian skin and hair. This study has shown that: 1. Apico-basal gradients of differentiation and different cell types are recognizable at the ultrastructural level in the developing feather germ. 2. The hypothesis that keratin is synthesized de novo by ribosomes is probably correct, because the largest number of these organelles is present at the time when keratin formation is most prominent. 3. Intercellular gaps in the developing feather germs facilitate the reorientation and rearrangement of different cell types into definitive feather structures. 4. The sources of nutrition and energy for the completion of keratinization during later developmental stages of feather germs are the supportive and the barb medullary cells and large stores of glycogen. 5. Keratohyalin granules are not precursors of feather keratin, since no such structures were observed in feather germs. 6. Two distinct modes of keratinization occur in feather germs. Keratinization in sheath cells is similar to that which occurs in mammalian epidermal cells. Barb and barbule cell keratinization resembles that of hair. 7. The basal lamina is probably involved in transport of synthetic material from the pulp cavity to the epidermal cells. The lamina may also provide mechanically strong connections between the feather germ and the dermis.