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Asymmetries related to those observed in catshark lateral habenulae are present in a lungfish and a polypterid, but undetectable in members of tetrapods and neopterygians. a,g,m Schemes showing the asymmetric organization of the catshark habenulae, with the reference signature markers of Left-LHb (a, yellow), MHb (g, purple) and Right-LHb (m, blue) considered for cross-species comparisons. b–f,h–l,n–r Transverse sections of habenulae in the elephant shark (stage 36 embryo) (b,h,n), the reedfish (juvenile) (c,i,o), the spotted gar (juvenile) (d,j,p), the African lungfish (juvenile) (e,k,q) and the Western clawed frog (stage NF-66 tadpole) (f,l,r), following ISH with probes for orthologs of catshark markers for Left-LHb (b–f), MHb (h–l) and Right-LHb (n–r). Dorsal is to the top in all panels and probe identity is indicated on each section. Black and white arrowheads in (b–f) and (n–r) respectively point to territories restricted to the left side and to the right side in the elephant shark, the reedfish and the lungfish, similar to the catshark, but bilateral in the spotted gar and the frog. Black arrows indicate the boundary between dorsal/medial and ventral/lateral habenulae. Dotted lines in (f,l,r) delineate the boundary between the lateral Sox1 habenular territory and the adjacent Prox1 territory in the frog. s–w Schemes showing territories related to catshark Left-LHb (yellow), MHb (purple) and Right-LHb (blue) in the elephant shark (s), the reedfish (t), the spotted gar (u), the lungfish (v) and the frog (w), based on the set of signature markers analyzed. Only markers supporting these relationships are indicated for each species, with those also expressed in additional territories labeled by an asterisk (see expression details in Supplementary Fig. 7–11). The same ISH profiles were consistently obtained for each gene and each species on at least three different specimens. Abbreviations: L, left; R, right. Scale bar = 500 µm in (b,h,n), 200 µm in (c,d,i,j,o,p), 150 µm in (e,k,q), 100 µm in (f,l,r).
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