AUTHOR=Shylo Natalia A. , Smith Sarah E. , Price Andrew J. , Guo Fengli , McClain Melainia , Trainor Paul A. 

TITLE=Morphological changes and two Nodal paralogs drive left-right asymmetry in the squamate veiled chameleon (C. calyptratus)

JOURNAL=Frontiers in Cell and Developmental Biology

VOLUME=11

YEAR=2023

URL=https://www.frontiersin.org/journals/cell-and-developmental-biology/articles/10.3389/fcell.2023.1132166

DOI=10.3389/fcell.2023.1132166

ISSN=2296-634X

ABSTRACT=<p>The ancestral mode of left-right (L-R) patterning involves cilia in the L-R organizer. However, the mechanisms regulating L-R patterning in non-avian reptiles remains an enigma, since most squamate embryos are undergoing organogenesis at oviposition. In contrast, veiled chameleon (<italic>Chamaeleo calyptratus</italic>) embryos are pre-gastrula at oviposition, making them an excellent organism for studying L-R patterning evolution. Here we show that veiled chameleon embryos lack motile cilia at the time of L-R asymmetry establishment. Thus, the loss of motile cilia in the L-R organizers is a synapomorphy of all reptiles. Furthermore, in contrast to avians, geckos and turtles, which have one <italic>Nodal</italic> gene, veiled chameleon exhibits expression of two paralogs of <italic>Nodal</italic> in the left lateral plate mesoderm, albeit in non-identical patterns. Using live imaging, we observed asymmetric morphological changes that precede, and likely trigger, asymmetric expression of the Nodal cascade. Thus, veiled chameleons are a new and unique model for studying the evolution of L-R patterning.</p>