Microscopic analysis of lizard claw morphogenesis and hypothesis on its evolution

Morphogenesis of claws in the lizard Lampropholis guichenoti has been studied by light and electron microscopy. Claws originate from a thickening of the epidermis covering the tips of digits under which mesenchymal cells aggregate. Mesenchymal cells are in continuity with perichondrial cells of the last phalange, and are connected to the epidermis through numerous cell bridges that cross an incomplete basement membrane. The dense lamella is completed in non-apical regions of the digit where also collagen fibrils increase. The dorsal side of the developing claw derives from the growth of the outer scale surface of the last scale of the digit. The corneous layer, made of beta-keratin cells, curves downward by the tip of the growing claw. The epidermis of the ventral side of the claw contains keratohyaline-like granules and alpha-keratinocytes like an inner scale surface. The thickness of the horny layer increases in the elongating unguis while a thinner and softer corneous layer remains in the subunguis. These observations show that lizard claws derive from the modification of the last scale or scales of the digit, probably under the influence of the growing terminal phalanx. Some hypotheses on the evolution of claws in reptiles are presented.

[1]  R. Reisz,et al.  Histological microstructure of the claws of the African clawed frog, Xenopus laevis (Anura: Pipidae): implications for the evolution of claws in tetrapods. , 2007, Journal of experimental zoology. Part B, Molecular and developmental evolution.

[2]  R. Reisz,et al.  The morphology of the terminal phalanges in Permo-Carboniferous synapsids: an evolutionary perspective , 2007 .

[3]  V. Toffolo,et al.  Scale keratin in lizard epidermis reveals amino acid regions homologous with avian and mammalian epidermal proteins. , 2006, The anatomical record. Part A, Discoveries in molecular, cellular, and evolutionary biology.

[4]  L. Alibardi.  Structural and immunocytochemical characterization of keratinization in vertebrate epidermis and epidermal derivatives. , 2006, International review of cytology.

[5]  L. Alibardi,et al.  Differentiation of the epidermis of scutes in embryos and juveniles of the tortoise Testudo hermanni with emphasis on beta-keratinization , 2005 .

[6]  T. Glenn,et al.  Evolutionary origin of the feather epidermis , 2005, Developmental dynamics : an official publication of the American Association of Anatomists.

[7]  J. Gillespie,et al.  A comparison of lizard claw keratin proteins with those of avian beak and claw , 2005, Journal of Molecular Evolution.

[8]  L. Alibardi.  Dermo-epidermal interactions in reptilian scales: speculations on the evolution of scales, feathers, and hairs. , 2004, Journal of experimental zoology. Part B, Molecular and developmental evolution.

[9]  D. Dhouailly,et al.  How and when the regional competence of chick epidermis is established: feathers vs. scutate and reticulate scales, a problem en route to a solution. , 2004, The International journal of developmental biology.

[10]  F. Michon,et al.  The different steps of skin formation in vertebrates. , 2004, The International journal of developmental biology.

[11]  C. Chuong,et al.  Evo-Devo of amniote integuments and appendages. , 2004, The International journal of developmental biology.

[12]  M. Hamrick,et al.  Evolution and development of mammalian limb integumentary structures. , 2003, Journal of experimental zoology. Part B, Molecular and developmental evolution.

[13]  H. Bragulla,et al.  Horse hooves and bird feathers: Two model systems for studying the structure and development of highly adapted integumentary accessory organs--the role of the dermo-epidermal interface for the micro-architecture of complex epidermal structures. , 2003, Journal of experimental zoology. Part B, Molecular and developmental evolution.

[14]  C. Tickle.  The early history of the polarizing region: from classical embryology to molecular biology. , 2002, The International journal of developmental biology.

[15]  S. Gilbert,et al.  Development of an evolutionarily novel structure: fibroblast growth factor expression in the carapacial ridge of turtle embryos. , 2001, The Journal of experimental zoology.

[16]  S. Gilbert,et al.  Morphogenesis of the turtle shell: the development of a novel structure in tetrapod evolution , 2001, Evolution & development.

[17]  L. Alibardi,et al.  Epidermal differentiation in the developing scales of embryos of the Australian scincid lizard Lampropholis guichenoti , 1999, Journal of morphology.

[18]  L. Alibardi,et al.  Morphogenesis of shell and scutes in the turtle Emydura macquarii , 1999 .

[19]  L. Alibardi.  Differentiation of the epidermis during scale formation in embryos of lizard , 1998, Journal of anatomy.

[20]  F. Casagranda,et al.  Sequence of a Glycine-Rich Protein from Lizard Claw: Unusual Dilute Acid and Heptafluorobutyric Acid Cleavages , 1987 .

[21]  R. Chapman.  Hair, Wool, Quill, Nail, Claw, Hoof, and Horn , 1986 .

[22]  P. Maderson,et al.  Morphological and biophysical identification of fibrous proteins in the amniote epidermis. , 1970, The Journal of experimental zoology.

[23]  E. Thorndike.  A microscopic study of the marmoset claw and nail. , 1968, American journal of physical anthropology.

[24]  W. F. Lever,et al.  The Ultrastructure of the Skin of Human Embryos: III. The Formation of the Nail in 16–18 Weeks Old Embryos * , 1966 .

[25]  R. Spearman,et al.  The effects of subcutaneous saline injections on growth and keratinization of mouse tail epidermis. , 1966, The Journal of investigative dermatology.