Potential activity of chicken amniotic fluid in epidermal development by promoting keratinocyte differentiation

Epidermal barrier formation during fetal development, a fundamental biological process in mammals and birds, occurs in the amniotic cavity filled with amniotic fluid (AF). In keratinocytes, indispensable proteins for barrier formation are produced during differentiation, including transglutaminase 1 (TG1) and structural proteins encoded by a gene cluster, epidermal differentiation complex. In general, the chicken fetus rapidly forms a robust epidermal barrier during a relatively short embryonic day (ED); however, little is known about how chicken AF (cAF) contributes to the controls of gene expression of the factors involved in epidermal development. Here, we first demonstrated that the cross-linking activity of TG1 gradually increased, followed by the development of barrier function until ED18 in the chicken fetal epidermis. Then, we revealed that cAF harvested at specific fetal stages had the ability to enhance the expression and activity of TG1, and to facilitate the expression of genes for the other epidermal transglutaminases, structural proteins, and differentiation-related transcription factors in human cultured keratinocytes. Furthermore, the thermal denaturation of cAF components reduced cAF efficacy in promoting the expression of those factors. The fractionated proteinaceous solution of cAF possessed the activity to induce the protein expression of barrier formation-related factors, such as the transcription factor zinc finger protein 750. These results indicated that proteinaceous molecules in cAF have the potential to activate the gene expression networks involved in epidermal barrier formation. This finding will provide novel insights into the physiological role of AF in fetal epidermal development.