Reversals of bodies, brains, and behavior

Abstract

Left–right asymmetries are highly prevalent throughout metazoan phyla, with bilaterally symmetrical organisms exhibiting well-conserved, consistently sided positioning and anatomy of visceral organs and central nervous system structures. Deviations from normal laterality constitute an important class of birth defects and much study has been devoted to the early mechanisms orienting the left–right axis during embryogenesis as well as lateralization of the brain. Far less understood are the potential links between laterality of the body and cognition, though recent work has begun to uncover a range of behaviors which are modified in organisms with altered left–right asymmetry. Here, we review regulatory events critical for the establishment of asymmetry and subsequent left–right patterning, using data from Xenopus, zebrafish, chick, Arabidopsis, and single cells, and discuss molecular and pharmacological reagents that disrupt these processes. We especially focus on behavioral assays which are sensitive to body laterality, presenting existing data for several model systems. Beyond classical conditioning and behavior screens, new automated machine vision platforms are powerful emerging tools to quantitatively examine the relationship between body asymmetry and lateralized and nonlateralized behaviors. This chapter serves as a primer for methods that allow the examination of cognitive and behavioral endpoints subsequent to molecular interventions in embryonic left–right asymmetry.