Immunohistochemical detection of sulfhydryl oxidase in chick skin appendages and feathers suggests that the enzyme contr
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ORIGINAL PAPER
Immunohistochemical detection of sulfhydryl oxidase in chick skin appendages and feathers suggests that the enzyme contributes to maturation of the corneous material Lorenzo Alibardi1 Received: 15 May 2020 / Revised: 21 August 2020 / Accepted: 26 August 2020 / Published online: 29 October 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Maturation of the corneous material of feathers, scutate scales, claws and beak is a special case of hard cornification since it mainly derives from the accumulation of small feather corneous beta proteins (FCBPs) of 9–12 kDa with a central betapleated sheet region, formerly indicated as feather beta keratins. FCBPs contain a relatively high amount of cysteines that likely form numerous –S-S- in the corneous material of these skin appendages. The present immunocytochemical study shows that sulfhydryl oxidase and FCBPs are associated in the differentiating keratinocytes and corneous layers of the epidermis, scales, claws, beak and barb-barbule cells during chick development. The enzyme appears localized in pre-corneous and corneous layers and in differentiating barb-barbule cells where it likely determines formation of -S-S- bonds. This maturation transformation completed in corneous layers of scales, beak, claws and feathers determines increase of hardness and mechanical resistance that, in feathers, is needed for protection and sustaining flight. The process of cornification in chick skin appendages and feathers is discussed in relation to the general process of formation of hard corneous material in vertebrate skin appendages. This occurs by the association of intermediate filament proteins (IFKs, formerly indicates as alpha-keratins) and keratin-associated proteins (KAPs) or CBPs. Keywords Avian skin · Feathers · Corneous proteins · Sulfhydryl oxidase · Immunolabeling
Introduction Different types of skin appendages or derivatives are present in land vertebrates, among which feathers represent the most complex corneous structure (Spearman 1964; Maderson 1970; Lucas and Stettenheim 1972; Sawyer et al. 1986; Chuong et al. 2003; Wu et al. 2004; Alibardi 2016a; Dhouailly et al. 2017). During avian development the skin gives rise to various appendages such as scales, claw, spurs, beak and feathers (Fig. 1). The complex and minute cell branching of feathers, barbs and barbules, derives from the formation of barb ridges during feather development (Fig. 1) or in the cyclical feather regeneration that occurs during the lifespan of birds. Details on the cell and tissue modification that take place during feather morphogenesis are described * Lorenzo Alibardi [email protected] 1
Comparative Histolab Padova and Department of Biology, University of Bologna, Via Selmi 3, 40126 Bologna, Italy
in details in numerous studies (Lucas and Stettenheim 1972; Sawyer et al. 1986; Chuong et al. 2000, 2003; Prum and Dyck 2003; Alibardi and Toni 2008; Alibardi 2009, 2016a, b; Maderson et al. 2009; Martinez-Calles et al. 2018). Cells of barbules and bar
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