Ultrastructure Features and Three-Dimensional Transmission Electron Tomography of Dhub Lizard (Uromastyx Aegyptia) Cornea and Its Adaptation to a Desert Environment

Abstract

We report ultrastructural features and transmission electron tomography of the dhub lizard (Uromastyx aegyptia) cornea and its adaptation to hot and dry environments. Six corneas of dhub lizards were fixed in 2.5% glutaraldehyde and processed for electron microscopy and tomography. The ultrathin sections were observed with a JEOL 1400 transmission electron microscope. The cornea of the dhub lizard is very thin (~28-30 µm). The epithelium constitutes ~14% of the cornea, whereas the stroma constitutes 80% of the cornea. The middle stromal lamellae are significantly thicker than anterior and posterior stromal lamellae. Collagen fibril (CF) diameters in the anterior stroma are variable in size (25-75 nm). Proteoglycans (PGs) are very large in the middle and posterior stroma, whereas they are small in the anterior stroma. Three-dimensional electron tomography was carried out to understand the structure and arrangement of the PG and CFs. The presence of large PGs in the posterior and middle stroma might help the animal retain a large amount of water to protect it from dryness. The dhub corneal structure is equipped to adapt to the dry and hot desert environment.

Cornea and its adaptation to environment and accommodation function in veiled chameleon (Chamaeleo calyptratus): ultrastructure and 3D transmission electron tomography

“…The lamellar organization of the chameleon was similar to the dhub lizard described by Akhtar et al (). In the dhub, lamellae in the anterior and posterior stroma were thin whereas in the middle stroma they were thick (Akhtar et al, ). Similar to the dhub lizard in the chameleon, the lamellae of the posterior stroma were thin whereas they were thick in the middle and posterior stroma.…”

“…The distribution of collagen fibril diameter in humans, tree shrews, zebrafish and camels is uniform throughout the stroma. In the dhub lizard, the percentage of large CF diameter (in the range of 45–55 nm), was very high in the anterior stroma (31.4%) whereas it was low in the middle (3.1%) and posterior stroma (0.6%) (Akhtar et al, ). Similar to dhub lizard, the diameter of collagen fibrils in the chameleon was not uniform throughout the stroma.…”

“…Images of lamellae, collagen fibrils and the attachment of the proteoglycans were captured with a bottom mounted Quamisa camera. Images of the distribution of proteoglycans without collagen fibrils were taken from the sections not stained with uranyl acetate and lead citrate as described by Akhtar et al ().…”

“…were taken from the sections not stained with uranyl acetate and lead citrate as described by Akhtar et al (2016).…”

“…The method for 3D imaging used here was described by Akhtar et al (2016). 120 digital images were taken from 260 to 1 60 degree angles to construct individual 3D images using the software program "Composer-x64, version 3.4.2.0" (Massachusetts Institute of Technology, USA).…”