Comparison of α and β keratin in reptiles

  • Nancy J. Alexander


The different patterns of keratin formation that have evolved in the class Reptilia are all variations of a common process. In Squamata (snakes and lizards), a sequence of layers composed of α or β keratin is formed periodically, after which the old epidermal generation is shed. In Chelonia (turtles and tortoises), the epidermis of the shell is composed of only β keratin, whereas the skin of the neck and leg is composed exclusively of α keratin. Molting in toto does not occur and shedding is a continuous process comparable to that in avian and mammalian epidermis. In Crocodilia (crocodiles, caimans, alligators) there is only a single layer of cornified cells, but the composition of the layer varies in different parts of the scale. The hinge regions have many of the morphological characteristics of α and β keratin whereas the center resembles β keratin. The living cells beneath contain accumulations of keratohyalin.

There are four ultrastructural characteristics of a keratinized α layer: 1) cellular outlines remain distinct, 2) a thickened plasma membrane forms during keratinization, 3) 80 Å filaments embedded in an amorphous matrix can be seen, and 4) PAS-positive material accumulates in extracellular spaces between the desmosomes.

The β layer exhibits none of these features. Instead the cells more or less (depending on species) coalesce into a compact layer which becomes attenuated in the hinge regions. A 30 Å filament pattern can be seen.

The mesos layer of squamates resembles the hinge region of crocodilians, exhibiting a combination of the characteristics of both α and β keratin.


Reptiles Skin Keratin Electron microscopy Evolution 


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  1. Alexander, N. J., Parakkal, P. F.: Formation of α- and β-type keratin in lizard epidermis during the molting cycle. Z. Zellforsch. 101, 72–87 (1969).Google Scholar
  2. Brody, I.: An ultrastructural study on the role of the keratohyalin granules in the keratinization process. J. Ultrastruct. Res. 3, 84–104 (1959).Google Scholar
  3. Bryant, S. V., Breathnach, A. S., Bellairs, A. A.: Ultrastructure of the epidermis of the lizard (Lacerta vivipara) at the resting stage of the sloughing cycle. J. Zool., Lond. 152, 209–219 (1967).Google Scholar
  4. Farquhar, M. G., Palade, G. E.: Cell junctions in amphibian skin. J. Cell Biol. 26, 263–291 (1965).Google Scholar
  5. Filshie, B. K., Rogers, G.E.: The fine structure of α-keratin. J. molec. Biol. 3, 784–786 (1961).Google Scholar
  6. —: An electron microscope study of the fine structure of feather keratin. J. biophys. biochem. Cytol. 13, 1–12 (1962).Google Scholar
  7. Flaxman, B. A., Maderson, P.F. A., Szabó, G., Roth, S. I.: Control of cell differentiation in lizard epidermis in vitro. Develop. Biol. 18, 354–374 (1968).Google Scholar
  8. Maderson, P. F. A.: Histological changes in the epidermis of snakes during the sloughing cycle. J. Zool. 146, 98–113 (1965).Google Scholar
  9. Maderson, P. F. A.: Observations on the epidermis of the tuatara (Sphenodon punctatus). J. Anat. 103, 311–320 (1968).Google Scholar
  10. —, Licht, P.: Epidermal morphology and sloughing frequency in normal and prolactin treated Anolis carolinensis (Iguanidae, Lacertilia). J. Morph. 123, 157–172 (1967).Google Scholar
  11. Matoltsy, A. G.: Keratinization of the avian epidermis. An ultrastructural study of the newborn chick skin. J. Ultrastruct. Res. 29, 438–458 (1969).Google Scholar
  12. —, Parakkal, P. F.: Membrane-coating granules of keratinizing epithelia. J. Cell Biol. 24, 297–307 (1965).Google Scholar
  13. —: Keratinization. In: Ultrastructure of normal and abnormal skin (A. Zelickson, ed.), p. 76–104. Philadelphia: Lea and Febiger 1967.Google Scholar
  14. Mercer, E. H.: Keratin and keratinization. 316 pp. New York: Pergamon Press, Inc. 1961.Google Scholar
  15. Odland, G. F.: A submicroscopic granular component in human epidermis. J. invest. Derm. 34, 11–15 (1960).Google Scholar
  16. —: Tonofilaments and keratohyalin. In: The epidermis. (W. Montagna and W. C. Lobitz, eds.), p. 237–249. New York: Academic Press, Inc. 1964.Google Scholar
  17. Parakkal, P. F.: The fine structure of anagen hair follicle of the mouse. In: Advances in Biology of skin, vol. IX, Hair growth (W. Montagna, ed.), p. 441–469. Oxford: Pergamon Press 1969.Google Scholar
  18. —, Matoltsy, A. G.: An electron microscopic study of developing chick skin. J. Ultrastruct. Res. 23, 402–416 (1968).Google Scholar
  19. Rogers, G. E.: Structural and biochemical features of the hair follicle. In: The epidermis (W. Montagna and W. C. Lobitz, eds.), p. 179–232. New York: Academic Press, Inc. 1964.Google Scholar
  20. Roth, S. I., Jones, W. A.: The ultrastructure and enzymatic activity of the boa constrictor (Constrictor constrictor) skin during the resting phase. J. Ultrastruct. Res. 18, 304–323 (1967).Google Scholar
  21. Rudall, K. M.: X-ray studies of the distribution of protein chain types in the vertebrate epidermis. Biochim. biophys. Acta (Amst.) 1, 549–562 (1947).Google Scholar
  22. Spearman, R. I. C.: The keratinization of epidermal scales, feathers and hairs. Biol. Rev. 41, 59–96 (1966).Google Scholar
  23. —, Riley, P. A. A.: Comparison of the epidermis and pigment cells of the crocodile with those in two lizard species. Zool. J. Linnean Soc. 48, 453–466 (1969).Google Scholar

Copyright information

© Springer-Verlag 1970

Authors and Affiliations

  • Nancy J. Alexander
    • 1
  1. 1.Oregon Regional Primate Research Center BeavertonOregonUSA

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