title: Simultaneous cell death and desquamation of the embryonic diffusion barrier during epidermal development.
abstract: The periderm is an epithelial layer covering the emerging epidermis in early embryogenesis of vertebrates. In the chicken embryo, an additional cellular layer, the subperiderm, occurs at later embryonic stages underneath the periderm. The questions arose what is the function of both epithelial layers and, as they are transitory structures, by which mechanism are they removed. By immunocytochemistry, the tight junction (TJ) proteins occludin and claudin-1 were localized in the periderm and in the subperiderm, and sites of close contact between adjacent cells were detected by electron microscopy. Using horseradish peroxidase (HRP) as tracer, these contacts were identified as tight junctions involved in the formation of the embryonic diffusion barrier. This barrier was lost by desquamation at the end of the embryonic period, when the cornified envelope of the emerging epidermis was formed. By TUNEL and DNA ladder assays, we detected simultaneous cell death in the periderm and the subperiderm shortly before hatching. The absence of caspases-3, -6, and -7 activity, key enzymes of apoptosis, and the lack of typical morphological criteria of apoptosis such as cell fragmentation or membrane blebbing point to a special form of programmed cell death (PCD) leading to the desquamation of the embryonic diffusion barrier.
authors.affiliation: Institute of Cell Biology and Bonner Forum Biomedizin, University of Bonn, D-53121 Bonn, Germany.
authors.forename: Manuela
authors.initials: M
authors.lastname: Saathoff
authors.forename: Barbara
authors.initials: B
authors.lastname: Blum
authors.forename: Thomas
authors.initials: T
authors.lastname: Quast
authors.forename: Gregor
authors.initials: G
authors.lastname: Kirfel
authors.forename: Volker
authors.initials: V
authors.lastname: Herzog
mesh_terms: D000818:Animals; D017209:Apoptosis; D020169:Caspases / Q000378:metabolism; D002645:Chickens; D062445:Claudin-1; D005314:Embryonic and Fetal Development; D000078404:Epidermal Cells; D004817:Epidermis / Q000737:chemistry / Q000254:growth & development*; D006735:Horseradish Peroxidase / Q000378:metabolism; D020287:In Situ Nick-End Labeling; D008565:Membrane Proteins / Q000378:metabolism; D062793:Occludin; D012867:Skin / Q000196:embryology* / Q000473:pathology*; D019108:Tight Junctions / Q000737:chemistry* / Q000648:ultrastructure
chemical_list: D062445:Claudin-1; D008565:Membrane Proteins; D062793:Occludin; D006735:Horseradish Peroxidase; D020169:Caspases