Escamas de reptiles

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Reptile scale paradigm: Evo-Devo, pattern formation and regeneration
By Cheng Chang, Ping Wu, Ruth E. Baker, Philip K. Maini, Lorenzo Alibardi, and Cheng-Ming Chuong

Como se sabe, las aves y mamíferos evolucionaron de los reptiles siendo estos últimos de suma importancia ya que fueron los que se adaptaron a la vida terrestre. Entre otras cosas, su integumento desarrolló barreras para prevenirla pérdida de agua, formó mecanismo para protegerse de la radiación ultravioleta, y escudos contra los rigores de la vida en la tierra.
A pesar de que la piel entre unos y otros organismos vertebrados como escamas, plumas, pelos y dientes sea tan distinta, comparten un número de similitudes durante su desarrollo en común: la proteína morfo genética del hueso Hedgehog (BMP) y la vía deseñalización Wnt.

El objetivo de este trabajo es subrayar la importancia de las escamas de reptiles como modelo experimental para un mejor entendimiento de la teoría Evo-Devo como integumento amniótico.

Tipos de Escamas en reptiles
Algunos tipos con características bastante insólitas son mostrados esquemáticamente en la Fig 2. Una iguana ejemplar verde (Iguana iguana) con tipos diferentes y elarreglos de escamas es mostrado en la Fig 3. Muestran algunas escamas inusuales modificadas en la Fig 4.

Fig. 2. Schematic drawings showing different types of reptile scales Scales (resting phase) are shown in multiple layers with names labeled in panel B. (A) Nonoverlapping tuberculate type scales. (B) Overlapping scales commonly seen in squamates. (C) Variations of microstructures from theOberhäutchen layer illustrating short spines in a, b and long setaes in c (such as those in the adhesive pad lamellae in geckos, Fig. 4B). (D) Pits on the scales of anole, gecko and iguana (mainly epidermal sensory organs; Fig. 4 E,F). (E) Tactile sensory organ on the hinge side of a scale in Agama. Some follicle-like structures have clustered dermal cells associated to their base; Fig. 4G). (F)Scales with ridges are seen on the back of skink or the neck of anole. (G) Frills, or very elongated scales, are seen on the back of iguana (Fig. 3B). (H) The horn on the head of chameleon contains a bony element core (osteoderm). (I) Scales on the limb of crocodilians show only minor overlapping. (J) Keeled scales with a central, elevated corneous ridge are seen on the dorsal body of crocodilians andsome armored agamid lizards (e.g. Australian spiny desert lizard or molok). Legends: a, fine ‘hair’ on scales of anoles; b, Micro-ornamentation on scales of snakes; c, Toe pad of anole or gecko;*, dermal cells clustered at the base of sensory organs in Agama; AK, α keratin; BK, β keratin; BP, bone element.

Fig. 3. Arrangement and different types of scales in iguana
(A) An adult iguana showingdifferent scale types in different regions (B–F). Left column: scales from regions designated in (A). Right column: H&E staining of their histological sections on the right. (B) Frills from the midline of the neck. Note the elongated scales compared with those in (C–F). (C) Scales from the dorsal trunk. (D) Scales from the ventral trunk. (E) Scales from the tail. (F) Tuberculate scales fromthe lateral neck region. Scale bars, 500 μm.

Fig. 4. Unusual scale types (A,B) Some scales have specialized surfaces to help them climb. (A) Toe pad of anole. (B) Longitudinal sections of digital pads shown in (A). Note the hairy structures on the setae are variations of the Oberhäutchen layer (Fig. 2C). (C,D) Some scales have dorsal ridges (keels) which increase the protective properties of thescales. (C) Dorsal skink scale with three ridges. (D) Cross section of an anole neck scale which exhibits one central ridge (Fig. 2F). (E–G) Some scales form pits, sensory organs with a simple structure at the dermalepidermal junction (Fig. 2D). (E) Low power view of the distal edge of a scale. (F) Detail of the pit sensory organ in (E) (arrow indicates the sensorial filament derived from...
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