1,721,107 research outputs found
Development, comparative morphology and cornification of reptilian claws in relation to claws evolution in tetrapods
No full textThe development of claws in different reptiles and their cornification are analyzed using histological, ultrastructural and autoradiographic methods. Claws develop at the tip of digits in relation to the growth of the terminal phalanx and appear as modified scales. The apical epidermis of digit becomes thickened and is associated with a mesenchymal condensation or a dense mesenchyme. The dorsal side of the digit becomes the unguis while the ventral side becomes the sub-unguis. The corneous layer in the unguis is thicker than in the sub-unguis and accumulates hard-keratin while corneocytes remain separated or partially fused. Bundles of hard-keratin tend to accumulate in parallel orientation with respect to the surface and are directed toward the claw tip. The sub-unguis is formed by a softer corneous material and by a much thinner hard-keratin layer. Autoradiography after tritiated thymidine and histidine injection indicates that the growth of reptilian claws occurs along the entire epidermis of the claw. A proximal matrix zone for cell proliferation like in mammalian nails and claws is therefore absent in claws of reptiles. This observation indicates that the pattern of growth of reptilian and probably avian claws is different from that of mammals
Morphology of setae in regenerating caudal adhesive pads of the gecko Lygodactylus capensis (Smith, 1849)
Full text linkAfter tail loss in the African gecko Lygodactylus capensis (Smith, 1949) a new tail is regenerated, including caudal adhesive pads. The axial skeleton of the regenerating tail consists in an elastic cartilaginous tube replacing the original vertebrae that allows interacting with the substrate like in the original tail. The formation of adhesive setae has been analyzed using transmission and scanning electron microscopy coupled to immunolabeling for Corneous Beta Proteins. During progressive stages of epidermal differentiation new setae are developed at stage 4 of the shedding cycle and contain Corneous Beta Proteins. These structural proteins are faintly localized in the Oberhautchen but are abundant in the beta-layer, indicating that the two epidermal layers have a different protein composition. The setae originate from the growth of Oberhautchen spinulae into the cytoplasm of clear cells and the latter produce a thick fibrous meshwork of keratin and other unknown proteins localized around the growing setae. This cytoskeleton likely allows molding tail setae like for digital setae. A graded development of setae is observed from the base to the tip of regenerated pads and from the periphery to more central areas. The terminal end of the setae is subdivided into numerous filamentous spatulae that increase the adhesion contact. Sensory boutons are frequently detected at the margin of tail scales and adhesive pads, likely improving compliance with the substrate. The present study indicates that tail regeneration is a convenient experimental model to analyze adhesive setae formation, microstructures that allow to these lizards climbing vertical and arboreal substrates
Wound keratins in the regenerating epidermis of lizard suggest that the wound reaction is similar in the tail and limb.
No full text[ARTICOLO
Immunolocalization and characterization of cornification proteins in snake epidermis.
No full text[ARTICOLO
Hydrogen and waste: Illusions, challenges and perspectives
No full textA strategy known
as ‘‘hydrogen economy’’ was proposed in the early 1970s and deeply
discussed since then. The debate has however raised a number of
technical issues which have hindered what was initially envisaged
as a triumphal ride towards a better future
Immunocytochemistry and protein analysis suggest that reptilian claws contain small high cysteine-glycine proteins.
No full textThe electrophoretic analysis of claw proteins indicate the presence of both alpha-keratin and cysteine-rich keratin associated beta-proteins of 12-17 kDa. The immunocytochemical localization confirma that claw contains beta-proteins associated to alpha-keratins
Electron microscopic analysis in the gecko Lygodactylus reveals variations in micro-ornamentation and sensory organs distribution in the epidermis that indicate regional functions
Full text linkPossible pattern variations of micro-ornamentation in different areas of the skin in the gecko Lygodactylus have been analyzed by scanning and transmission electron microscopy. A map of micro-ornamentation present in various areas of the skin has been obtained. Differences in micro-ornamentation pattern and sensory organ distribution were detected. The “spinulated pattern” consists of shorter spinulae in dorsal versus ventral scales, and spinules are shorter in inner scale surface and hinge regions with respect to the outer scale surface. The spines derive from the accumulation of struts of corneous material mainly composed of corneous beta proteins (CBPs, formerly indicated as beta-keratins) that merge into pointed micro-ornamentation. The 3D-accumulation of CBPs within Oberhautchen cells can vary in some regions of different scales during Oberhautchen-beta cell differentiation, perhaps also under physical tensile forces derived from continuous scale growth. Three other main patterns of micro-ornamentation were detected and indicated as “corneous belts,” “corneous dendritic ramification,” and “serpentine-pit and groove.” These variations from the typical spinulated pattern present in gecko epidermis are interpreted as transitional regions where the accumulation of corneous material in Oberhautchen cells that merges with underlying beta-cells gives rise to nonspinulated surfaces. Spinulated sensory organs with bristles and lenticular-shaped or knob-like tactile corpuscles are more numerous in ventral scales of the tail tip close to adhesive pads and near the digital pads. These regions are likely those most involved in the fine control of movements and response to vibrational stimuli derived from air and objects movements, including potential preys or predators
Isolation of a new class of cysteine-glycine-proline-rich beta-proteins (beta-keratins) and their expression in snake epidermis.
No full textScales of snakes contain hard proteins (beta-keratins), now referred to as keratin-associated beta-proteins. In the present study we report the isolation, sequencing, and expression of a new group of these proteins from snake epidermis, designated cysteine-glycine-proline-rich proteins. One deduced protein from expressed mRNAs contains 128 amino acids (12.5 kDa) with a theoretical pI at 7.95, containing 10.2% cysteine and 15.6% glycine. The sequences of two more snake cysteine-proline-rich proteins have been identified from genomic DNA. In situ hybridization shows that the messengers for these proteins are present in the suprabasal and early differentiating beta-cells of the renewing scale epidermis. The present study shows that snake scales, as previously seen in scales of lizards, contain cysteine-rich beta-proteins in addition to glycine-rich beta-proteins. These keratin-associated beta-proteins mix with intermediate filament keratins (alpha-keratins) to produce the resistant corneous layer of snake scales. The specific proportion of these two subfamilies of proteins in different scales can determine various degrees of hardness in scales
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