Lamellar bodies bind the early cornified envelope

Lamellar bodies (LBs) ) are lipid-rich organelles produced by keratinocytes and secreted to form an impermeable water barrier (Feingold & Elias 2014). The lipids in LBs contain phospholipids, glucosylceramides, sphingomyelin and cholesterol (Feingold 2007). These lipids, some of which are keratinization specific, are synthesized and accumulate in the trans Golgi apparatus, budding off as LBs that accumulate in the granular layer (Wertz & van den Bergh 1998). ). LB lipids also organize into characteristic intercellular lamellae (Kalinin et al. 2002). LBs fuse with the plasma membrane (Schmitz & Muller 1991, Chattopadhyay et al. 2003) delivering lipids which become ester-linked to involucrin and probably other cornified envelope proteins by TG1 (Nemes et al. 1991) and possibly TG5 (Candi et al. 2005), forming a monomolecular layer termed the lipid envelope. Eventually these lipids replace the plasma membrane lipid bilayer, which is reabsorbed. Extracellularly, the LB lipids are further metabolized to have a unique composition and are 50% ceramides, 25% cholesterol, and 15% free fatty acids (Feingold 2007).

层状体（LBs）是由角质形成细胞产生并分泌形成的富含脂质的细胞器，其作用在于构建一种不可渗透的水性屏障（Feingold & Elias 2014）。层状体中的脂质包括磷脂、葡萄糖神经酰胺、鞘磷脂和胆固醇（Feingold 2007）。这些脂质中，部分具有角质化特异性，它们在转运高尔基体中合成并积累，形成层状体并累积于颗粒层（Wertz & van den Bergh 1998）。层状体脂质亦会组织成典型的细胞间层状结构（Kalinin et al. 2002）。层状体与质膜融合（Schmitz & Muller 1991, Chattopadhyay et al. 2003），将脂质传递至质膜，这些脂质通过TG1（Nemes et al. 1991）及可能TG5（Candi et al. 2005）与角蛋白和可能的其他角质化包被蛋白以酯键结合，形成被称为脂质包被的单分子层。最终，这些脂质替代了质膜脂质双层，后者被重新吸收。在细胞外，层状体脂质进一步代谢，形成独特的组成，其中包含50%的神经酰胺、25%的胆固醇和15%的游离脂肪酸（Feingold 2007）。