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Dev Dyn 2023 Nov 01;25211:1375-1390. doi: 10.1002/dvdy.594.
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Common features of cartilage maturation are not conserved in an amphibian model.

Nguyen JKB , Gómez-Picos P , Liu Y , Ovens K , Eames BF .

BACKGROUND: Mouse, chick, and zebrafish undergo a highly conserved program of cartilage maturation during endochondral ossification (bone formation via a cartilage template). Standard histological and molecular features of cartilage maturation are chondrocyte hypertrophy, downregulation of the chondrogenic markers Sox9 and Col2a1, and upregulation of Col10a1. We tested whether cartilage maturation is conserved in an amphibian, the western clawed frog Xenopus tropicalis, using in situ hybridization for standard markers and a novel laser-capture microdissection RNAseq data set. We also functionally tested whether thyroid hormone drives cartilage maturation in X tropicalis, as it does in other vertebrates. RESULTS: The developing frog humerus mostly followed the standard progression of cartilage maturation. Chondrocytes gradually became hypertrophic as col2a1 and sox9 were eventually down-regulated, but col10a1 was not up-regulated. However, the expression levels of several genes associated with the early formation of cartilage, such as acan, sox5, and col9a2, remained highly expressed even as humeral chondrocytes matured. Greater deviances were observed in head cartilages, including the ceratohyal, which underwent hypertrophy within hours of becoming cartilaginous, maintained relatively high levels of col2a1 and sox9, and lacked col10a1 expression. Interestingly, treating frog larvae with thyroid hormone antagonists did not specifically reduce head cartilage hypertrophy, resulting rather in a global developmental delay. CONCLUSION: These data reveal that basic cartilage maturation features in the head, and to a lesser extent in the limb, are not conserved in X tropicalis. Future work revealing how frogs deviate from the standard cartilage maturation program might shed light on both evolutionary and health studies.

PubMed ID: 37083105
Article link: Dev Dyn
Grant support: [+]

Species referenced: Xenopus tropicalis Xenopus laevis
Genes referenced: acan bmp6 col10a1 col2a1 col9a1 col9a2 col9a3 epyc fmod ibsp ifitm5 ihh matn1 mef2c mgp mmp13 mybpc1 mybpc2 mybpc3 myf5 myf6 myh7 myl2 myog myot myoz1 runx2 sox6 sox9 sp7
GO keywords: metamorphosis [+]
Antibodies: Col2a1 Ab1

Article Images: [+] show captions