Fig. 8. Schematic of habenular domains and efferent projections in larval zebrafish. (A) Six asymmetric domains in L-R habenular nuclei of 4-day larvae are defined by lov, ron and dex expression. The left habenula is divided into one dorsal and three ventral domains, while four expression domains are organized along the anterior-posterior axis of the right habenula. (B) Normally, left habenular Lov⁺ Ron^– neurons (domain i) project to the dorsal IPN. Ron⁺ efferents from both habenulae (domains ii, iii, v and vi) project to the ventral IPN. (C) In larvae with reversed epithalamic laterality, FR projections are L-R reversed, but DV innervation of the IPN is unaffected. (D) In parapineal-ablated larvae, the left habenula adopts molecular properties characteristic of the right habenula. The dorsal IPN shows a partial loss of Lov⁺ axons, while the ventral IPN shows increased immunoreactivity. Remaining Lov⁺ axons at the dorsal IPN may represent an incomplete transformation of the left habenula to right habenular fate.