Fig. 6

Genoarchitectonic signatures of the hypothalamo-prethalamic primordium (HyPTh) (II).

(A-A′′) IrxA mRNA expression is observed from the HyPTh/Di-Mesencephalic primordium (DiMes) boundary extending caudally to the rostral portion of the Rhombencephalo-Spinal primordium (RhSp) domain. (B-B′′) IrxC mRNA expression is observed from the HyPTh/DiMes boundary, extending caudally to the rostral portion of the RhSp domain. (C-D′′) Lhx2/9b marks the alar plate in the Rostral-HyPTh and Intermediate-HyPTh domains (C-C′′), as shown by a gap of expression in a double in situ hybridization between Lhx2/9b and IrxC (D-D′′). The lateral view of Six3/6 expression (inset in C) is provided for comparison with Lhx2/9b and highlights the restricted expression of Six3/6 to the Rostral-HyPTh (compare the region between the arrow and the single arrowhead, which corresponds to the Rostral-HyPTh and Intermediate-HyPTh domains, with the region between the arrow and double arrowhead, which includes only the Rostral-HyPTh domain (C,C′)). On the other hand, a dorsal view of Fezf (inset in C′) shows expression across both the alar and basal plates of the HyPTh. (E,E′′) Lhx1/5 mRNA expression is observed only in the basal plate of the HyPTh and DiMes primordia and in some RhSp subdivisions (see inset in C′ for comparison). (F-F′′) Otp is a key hypothalamic marker in vertebrates but was only found in amphioxus in one domain at the RhSp region. (G-H′′) Wnt3 and Wnt7 mRNAs were detected from the DiMes/RhSp border, extending caudally in the entire RhSp region. Expression patterns correspond to lateral (A-G) or dorsal views (A′-G′) at the 21 h post fertilization (hpf) embryonic stage and are represented in schematics dorsal views (A′′-G′′). Somites (dotted lines) were used as main landmarks to localize the position of the patterns analyzed in the late neural plate. Scale bar: 50 μm.