How the brain becomes lateralized is poorly understood. By contrast, much is known about molecular cues that specify the left-right axis of the body, fashioning the asymmetric morphology and positioning of the visceral organs. In zebrafish, the Nodal signaling pathway functions in visceral asymmetry and also in the embryonic brain, to bias laterality of the epithalamus. Formation of an asymmetric pineal complex differentially influences adjacent diencephalic nuclei, the left and right habenulae, which acquire distinctive molecular and cellular features. Results from the genetically tractable zebrafish system provide a promising entry point for exploring how left-right biases are established and propagated in the developing vertebrate brain.
Bibliographical noteFunding Information:
We are grateful to Christine Thisse and Bernard Thisse for generously providing zebrafish brain markers and to Chris Wright and Luis Puelles for valuable discussions. Described research was supported in part by the NSF (M.E.H.) and by post-doctoral fellowships from NRSA (J.O.L.) and the American Cancer Society (J.T.G.).