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Abstract T lymphocytes or T cells are key components of the vertebrate response to pathogens and cancer. There are two T cell classes based on their TCRs, αβ T cells and γδ T cells, and each plays a critical role in immune responses. The squamate reptiles may be unique among the vertebrate lineages by lacking an entire class of T cells, the γδ T cells. In this study, we investigated the basis of the loss of the γδ T cells in squamates. The genome and transcriptome of a sleepy lizard, the skink Tiliqua rugosa, were compared with those of tuatara, Sphenodon punctatus, the last living member of the Rhynchocephalian reptiles. We demonstrate that the lack of TCRγ and TCRδ transcripts in the skink are due to large deletions in the T. rugosa genome. We also show that tuataras are on a growing list of species, including sharks, frogs, birds, alligators, and platypus, that can use an atypical TCRδ that appears to be a chimera of a TCR chain with an Ab-like Ag-binding domain. Tuatara represents the nearest living relative to squamates that retain γδ T cells. The loss of γδTCR in the skink is due to genomic deletions that appear to be conserved in other squamates. The genes encoding the αβTCR chains in the skink do not appear to have increased in complexity to compensate for the loss of γδ T cells.
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Biomechanical behaviour of lizard osteoderms and skin under external loading
ABSTRACT Many species of lizards are partially enveloped by a dermal armour made of ossified units called osteoderms. Lizard osteoderms demonstrate considerable species-specific variation in morphology and histology. Although a physical/protective role (against predators, prey, conspecifics and impact loading during falls) is frequently advanced, empirical data on the biomechanics of lizard osteoderms are scarce, limiting our understanding of form–function relationships. Here, we report deformation recorded at the surface of temporal osteoderms during controlled external loading of preserved specimens of 11 lizard species (Tiliqua rugosa, Tiliqua scincoides, Corucia zebrata, Pseudopus apodus, Timon lepidus, Matobosaurus validus, Broadleysaurus major, Tribolonotus gracilis, Tribolonotus novaeguineae, Heloderma horridum and Heloderma suspectum). Based on the strain recorded in situ and from isolated osteoderms, the skin of the species investigated can be ranked along a marked stiffness gradient that mostly reflects the features of the osteoderms. Some species such as T. rugosa and the two Heloderma species had very stiff osteoderms and skin while others such as T. lepidus and P. apodus were at the other end of the spectrum. Histological sections of the osteoderms suggest that fused (versus compound) osteoderms with a thick layer of capping tissue are found in species with a stiff skin. In most cases, loading neighbouring osteoderms induced a large strain in the instrumented osteoderm, attesting that, in most species, lizard osteoderms are tightly interconnected. These data empirically confirm that the morphological diversity observed in lizard osteoderms is matched by variability in biomechanical properties.
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- Award ID(s):
- 1902242
- PAR ID:
- 10555905
- Publisher / Repository:
- The Company of Biologists
- Date Published:
- Journal Name:
- Journal of Experimental Biology
- Volume:
- 225
- Issue:
- 20
- ISSN:
- 0022-0949
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1242/jeb.244551
