Distinguished University Professor University of Maryland College Park, Maryland, United States
Astyanax mexicanus is a single teleost species consisting of surface dwelling (surface fish) and cave-dwelling (cavefish) morphs, which show differences in visceral organ asymmetry. Surface fish show situs solitus, the conventional mode of left-right asymmetry in vertebrates. In contrast, cavefish show high levels of situs inversus, including reversals in left-sided expression of the Nodal/Pitx2 signaling system and the direction of cardiac tube looping. Genetic analysis indicates that the changes in cavefish heart asymmetry are under maternal control. The zygotic target of the maternal effects is the structure and function of the left-right organizer, which establishes left-right asymmetry through lateralizing the Nodal/Pitx2 system. The environmental cue responsible for the evolutionary changes in cavefish left-right asymmetry is hypoxia, which is prevalent in the dark cave environment due to the lack of photosynthesis. Therefore, we are beginning to understand the evolution of left-right asymmetry from its origin to its eventual phenotypic consequences in the A. mexicanus system.
