The Silent Twist: How Chameleon Embryos Break Symmetry Differently

The article titled "Embryonic Asymmetry in Veiled Chameleons: A Model for Reptilian Left-Right Patterning"explores how left-right (L-R) asymmetry develops in Chamaeleo calyptratus embryos, offering a valuable reptilian model for understanding vertebrate embryogenesis. The study focuses on the timing and molecular mechanisms that establish asymmetry in internal organs, such as the heart and gut. Unlike mammals and birds, veiled chameleons exhibit a delayed onset of asymmetry, with visible organ looping occurring much later in development.

Researchers used in situ hybridization to track the expression of key genes like Nodal, Lefty, and Pitx2, which are known to regulate L-R patterning in other vertebrates. They found that these genes are expressed asymmetrically in the lateral plate mesoderm, but at a later developmental stage than in other amniotes. This suggests that chameleons may use a conserved genetic toolkit but with a shifted temporal framework, possibly linked to their unique embryonic development, which includes a prolonged gastrulation phase.

The study also highlights the absence of a node-like structure in chameleon embryos, a feature typically involved in symmetry breaking in other species. This raises intriguing questions about how asymmetry is initiated in reptiles and whether alternative mechanisms are at play. The authors propose that veiled chameleons offer a comparative model to study evolutionary variations in L-R patterning and may help uncover ancestral traits in amniote development.

Overall, the research provides foundational insights into reptilian embryology and underscores the importance of expanding developmental studies beyond traditional model organisms.

Origtinal Article:

Diaz, R. E., & Trainor, P. A. (2023). Embryonic Asymmetry in Veiled Chameleons: A Model for Reptilian Left-Right Patterning. Frontiers in Cell and Developmental Biology, 11, 1132166. https://doi.org/10.3389/fcell.2023.1132166.