Apoptosis and the Development of Avian Integument:
Feathers and Periderm

Christopher Reamer and Sue Ann Miller, Department of Biology, Hamilton College, Clinton, New York

Illustrations below

Apoptosis, also known as programmed cell death or PCD, is a specific form of non-random cell death that is an integral part of vertebrate development. PCD is involved with mammalian and avian digital development and epidermal cell differentiation in chick embryos (Carlson, 1999), but the potential role of apoptosis in development of the avian integument has not been examined. We investigated the role of apoptosis in early feather morphogenesis and shedding of the late-stage periderm in chick embryos.

We examined the feather development and periderm sloughing processes by employing an in situ immunomarker for apoptosis (ApopTag®, Intergen). Feather and skin tissue sections from White Leghorn chicken embryos (SPAFAS) at 14, 16, and 18 days of incubation were studied. Apoptotic cells were marked in feather sections from chicks at all three ages. Positive markers were observed in the distal end of 14-day feathers. 16-day feathers showed light staining which was localized in the mid-axial region of developing feathers. Sections of 18-day feathers showed positively marked apoptotic cells in the feather follicle. Apoptotic bodies within feathers were observed mainly in the thin layer of epithelium bounding the medulla of the ramus within individual barb ridges. Apoptotic cells within the feather were distributed along the longitudinal axis of the feather, and localized distal to proximal with increasing age. Periderm sections of 14- and 16-day chicks showed no marked cells, whereas periderm sections from 18-day chicks showed abundant and very clearly marked apoptotic cells.

This preliminary investigation supports our hypothesis that apoptosis plays a role in both sculpting of feathers and shedding of the periderm. As is the case with cell differentiation within the feather, apoptosis seems to move proximally along the longitudinal axis of the feather as development progresses. Furthermore, there is strong evidence to suggest that the loss of the periderm is temporally specific, and does not occur until day 18 of incubation. This finding is in agreement with earlier observations of timing of periderm loss (Bellairs and Osmond, 1998). Apoptosis appears to be the mechanism by which the periderm is removed.

Grant sponsor: Sigma Xi Grant-in-Aid of Research; Grant sponsor: The Hamilton College Academic Fund for Seniors.

Chris presented this research as a poster at "Celebrating Student Research at the Millennium", a Sigma Xi Student Research Symposium held at St. Joseph's University in Philadelphia on 28 April 2000. His travel to present his work was funded by the Biology Department Student Travel Fund. A full manuscript is in preparation as earlier stages are currently being studied to provide a more complete understanding of patterns of cell death and documentation of cell division.

Apoptosis in Feather Sections  
Brown nuclei mark apoptosis in all figures.

14-day distal feather section: Strong positive markers are localized in the distal tips of 14-day feathers and are bound to the outside of the medulla of the ramus. Proximal sections of a feather bud do not mark for apoptosis. Marginal and axial plates have already been removed by day 14 of incubation.

16-day mid-axial feather section: Positive markers surround the medulla of the ramus with a mid-axial localization. Feathers have begun to keratinize by day 16 of incubation, which makes obtaining sections difficult.

16-day [A] and 18-day [B] follicle sections: Sections of 18-day feather follicle mark for apoptosis where there were no markers at 16 days. Undifferentiated calamus of the feather within the follicles contains many positively stained nuclei that appear to occur randomly within the follicle.

Apoptosis in Periderm Sections
Black arrows indicate the periderm layer.  

14-day periderm

16-day periderm
18-day periderm
No apoptosis markers in apparently healthy and functioning periderm layer.
Many apoptotic nuclei localize in the periderm.

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Created 1 May 2000   Last Modified: 11 August 2003