Immunocytochemical localization and biochemical analysis of α and β keratins in the avian lingual epithelium

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Abstract
The α and β keratins are found as 10-nm and 3-nm cytoplasmic filaments, respectively. While the a keratins are produced in essentially all vertebrate epithelia (Franke et al.: Exp. Cell Res., 116:429-445, 1978; Sun et ah: Proc. Natl. Acad. Set. USA, 76:2813–2817, 1979), the β keratins have been demonstrated only in specific epithelial tissues of birds and reptiles (Sawyer et ah: In: Biology of the Integument: Vertebrates. J. Bereiter-Hahn, A.G. Matoltsy, and K, S. Richards, eds. Springer-Verlag, Berlin, Vol. 2, pp. 194–238,1986; Land-mann: In: Biology of the Integument: Vertebrates. J. Bereiter-Hahn, A.G. Matoltsy, and K.S. Richards, eds. Springer-Verlag, Berlin, Vol. 2, pp. 150–187, 1986). Recently, Homberger and Brush (Zoomorphology, 106:103-114, 1986) have demonstrated that within the lingual epithelium of parrots, β keratins are expressed exclusively in the anterior ventral region. While it is well established that epidermal-dermal interactions are important for the regional expression of the β keratin genes in the avian scutate scales and feathers, little is known about the expression of β keratins in other epithelial structures such as the tongue. We have used biochemical and immunocytochemical techniques to analyze the a and β keratins of the lingual epithelium of the chick as an initial step in the characterization of this model system for developmental studies. We have found that α keratins are present throughout the lingual epithelium. The anterior ventral epithelium contains α keratin polypeptides characteristic of skin-type differentiation, while the epithelium of the dorsal and posterior ventral regions contains α keratin polypeptides characteristic of esophageal-type differentiation (O'Guin et al.: In: Current Topics in Developmental Biology: The Molecular and Developmental Biology of Keratins. A.A. Moscona and A. Monroy, eds. R.H. Sawyer, vol. ed. Academic Press, New York, Vol. 22, pp. 282–306, 1987). Beta keratins are produced only in the differentiated epithelial cells of the anterior ventral region of the tongue. Immunoelectron microscopy demonstrates that the α and β keratins of the stratum intermedium and corneum of the anterior ventral region are found together in the large filament bundles characteristic of this region. The preexistence of the α keratins in the cells destined to produce β keratins as well as the colocalization of these keratins in the filament bundles of these cells suggests that a functional relationship may exist between the α. and β keratins.